JP2008139817A - Fixer and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fixer and an image forming apparatus, in which pressure is optimized and excellent fixing properties are stably secured, in a nip by accurately and simply obtaining the variable relative pressure of a pressure member with respect to a fixing member, when the relative pressure of the pressure member with respect to the fixing member is made variable. <P>SOLUTION: The fixer for the image forming apparatus includes the fixing member 21 configured to fuse a toner image with heat, the pressure member 31 configured to press against the fixing member 21 to form the nip therebetween, variable means 45 to 48, 52 and 53 configured to vary the relative pressure of the pressure member 31 with respect to the fixing member 21 by changing the rotation position of a cam 48, and a drive motor 52 to drive the cam 48 to rotate. Then, the rotation position of the cam 48 is detected by detecting changes in an electrical current that flows in the drive motor 52 when the cam 48 is rotated. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a copying machine, a printer, a facsimile, or a complex machine thereof, and a fixing device installed therein, and in particular, a fixing device that varies a pressure applied by a pressure member to a fixing member and The present invention relates to an image forming apparatus.

Conventionally, in an image forming apparatus such as a copying machine or a printer, a fixing member such as a fixing roller, a fixing belt, or a fixing sleeve and a pressure member such as a pressure roller or a pressure belt are brought into contact with each other to form a nip portion. 2. Description of the Related Art Fixing devices that form and transport a recording medium to the nip portion to fix a toner image on the recording medium are widely used.
In such a fixing device, a technique for changing the pressure of the pressure member with respect to the fixing member is widely used (see, for example, Patent Document 1 to Patent Document 3).

  Specifically, in Patent Document 1 and the like, a pressure lever is provided at the shaft portion of the pressure member (pressure roller) in order to press the fixing member (fixing roller). A cam is engaged with the pressure lever, and the pressure member is brought into contact with and separated from the fixing member by rotating the cam using a motor.

On the other hand, Patent Document 2 and the like disclose a technique for arbitrarily adjusting the pressing force (pressing condition) of the pressing member with respect to the fixing member in order to prevent deformation of the elastic layer of the fixing member (fixing belt). Yes.
Patent Document 3 and the like disclose a fixing device that contacts and separates a pressure member with respect to a fixing member by rotation of a cam, and detects a rotation state of the cam with a micro switch that contacts the cam. .

JP-A-2005-201918 JP 2005-114959 A Japanese Utility Model Publication No. 58-195255

  In the conventional technology described above, the pressure state of the pressure member with respect to the fixing member has not been accurately and easily grasped. For this reason, a desired pressurizing force cannot be obtained at the nip portion, and sufficient fixability may not be ensured.

Such a problem is not particularly negligible when trying to optimize the nip amount by varying (finely adjusting) the pressing force in the nip portion according to the paper type (paper thickness) of the recording medium. .
Even when an elastic layer made of foamed rubber is provided on the fixing member or pressure member in order to ensure a sufficient nip amount even if the diameter of the fixing member or pressure member is reduced, the elastic layer is always subjected to a load and hardness. In order to suppress the occurrence of lowering, bubble breakage, and compression set, the above-mentioned problem cannot be ignored because the pressure applied at the nip portion is frequently changed.

In order to solve such a problem, an optical sensor is used to optically detect the posture (rotational position) of the cam in the rotational direction, or the rotational direction of the cam can be detected using a microswitch as in Patent Document 3 or the like. A measure to detect the posture mechanically is also conceivable.
However, in that case, it is necessary to secure an installation space for the optical sensor or the microswitch, or it is necessary to install a member related to the optical sensor or the microswitch (for example, a harness or a light shielding plate). The shape of the cam is restricted.

  The above-described problem is not limited to a heater lamp heating type fixing device using a heater or the like as a heat source, but is common to other types of fixing devices such as an electromagnetic induction heating method.

  The present invention has been made to solve the above-described problems. When the relative pressing force of the pressing member with respect to the fixing member is changed, the changing pressing force is accurately and easily grasped. Another object of the present invention is to provide a fixing device and an image forming apparatus in which a pressing force is optimized at a nip portion and good fixing performance is stably secured.

  According to a first aspect of the present invention, there is provided a fixing device that heats and melts a toner image, a pressure member that presses against the fixing member to form a nip portion, and changes a rotational position of the cam. And a variable motor that varies the relative pressure of the pressure member relative to the fixing member, and a drive motor that rotationally drives the cam, and a current that flows through the drive motor when the cam is rotationally driven. The rotational position of the cam is detected by detecting a change in value.

  The fixing device according to a second aspect of the present invention is the fixing device according to the first aspect, wherein the cam includes a plurality of pressure contact regions corresponding to the variable desired pressing force and the pressure contact adjacent to the rotation direction. A plurality of transition regions for transition to the region, and the plurality of transition regions are formed such that the distance from the rotation center axis of the cam greatly varies as the cam rotates. Is.

  According to a third aspect of the present invention, in the fixing device according to the second aspect of the present invention, at least one of the plurality of pressure contact areas makes the applied pressure zero.

According to a fourth aspect of the present invention, there is provided the fixing device according to the second or third aspect, wherein the first print time in the image forming apparatus is T1, and the recording medium is started after conveyance of the recording medium is started. When the time until the medium reaches the nip portion is T2, the rotational drive time T of the cam for moving to any one of the plurality of pressure contact areas is:
T ≦ T1-T2
Satisfy the relationship.

  The fixing device according to a fifth aspect of the present invention is the fixing device according to any one of the first to fourth aspects, wherein the variable means rotates the cam in the forward and reverse directions by the drive motor. The pressure force is configured to increase or decrease.

  A fixing device according to a sixth aspect of the present invention is the fixing device according to any one of the first to fifth aspects, wherein the drive motor is a DC motor.

  A fixing device according to a seventh aspect of the present invention is the fixing device according to any one of the first to sixth aspects, wherein at least one of the fixing member and the pressing member is made of foamed rubber. With a layer.

  An image forming apparatus according to an eighth aspect of the present invention includes the fixing device according to any one of the first to seventh aspects.

  The present invention detects the current value of the drive motor that rotationally drives the cam when the cam is rotated to vary the relative pressure of the pressure member with respect to the fixing member. It is possible to provide a fixing device and an image forming apparatus that can be accurately and simply grasped and the pressing force is optimized at the nip portion to ensure a stable fixing property.

  Hereinafter, the best mode for carrying out the present invention will be described in detail with reference to the drawings. In addition, in each figure, the same code | symbol is attached | subjected to the part which is the same or it corresponds, The duplication description is simplified or abbreviate | omitted suitably.

Embodiment 1 FIG.
The first embodiment of the present invention will be described in detail with reference to FIGS.
First, the configuration and operation of the entire image forming apparatus will be described with reference to FIG.
In FIG. 1, reference numeral 1 denotes an apparatus main body of a copying machine as an image forming apparatus, 2 an original reading unit that optically reads image information of an original D, and 3 an exposure light L based on image information read by the original reading unit 2. Is exposed to the photosensitive drum 5, 4 is an image forming unit for forming a toner image (image) on the photosensitive drum 5, and 7 is a toner image formed on the photosensitive drum 5 on the recording medium P. A transfer unit 10 for transferring, a document transport unit for transporting the set document D to the document reading unit 2, 12 to 14 a paper feed unit storing a recording medium P such as transfer paper, and 20 on the recording medium P A fixing device for fixing an unfixed image, 21 is a fixing belt as a fixing member installed in the fixing device 20, and 31 is a pressure roller as a pressure member installed in the fixing device 20.

With reference to FIG. 1, an operation during normal image formation in the image forming apparatus will be described.
First, the document D is conveyed from the document table in the direction of the arrow in the drawing by the conveyance roller of the document conveyance unit 10 and passes over the document reading unit 2. At this time, the document reading unit 2 optically reads the image information of the document D passing above.
Then, the optical image information read by the document reading unit 2 is converted into an electric signal and then transmitted to the exposure unit 3 (writing unit). Then, exposure light L such as laser light based on the image information of the electrical signal is emitted from the exposure unit 3 toward the photosensitive drum 5 of the image forming unit 4.

On the other hand, in the image forming unit 4, the photosensitive drum 5 is rotated in the clockwise direction in the drawing, and image information is transferred onto the photosensitive drum 5 through a predetermined image forming process (charging process, exposure process, development process). An image (toner image) corresponding to is formed.
Thereafter, the image formed on the photosensitive drum 5 is transferred by the transfer unit 7 onto the recording medium P conveyed by the registration roller.

On the other hand, the recording medium P conveyed to the transfer unit 7 operates as follows.
First, one of the plurality of paper feeding units 12, 13, and 14 of the image forming apparatus main body 1 is automatically or manually selected (for example, the uppermost paper feeding unit 12 is selected). To do.)
Then, the uppermost sheet of the recording medium P stored in the paper feeding unit 12 is transported toward the position of the transport path K.

  Thereafter, the recording medium P passes through the conveyance path K and reaches the position of the registration roller. Then, the recording medium P that has reached the position of the registration roller is conveyed toward the transfer unit 7 at the same timing in order to align with the image formed on the photosensitive drum 5.

After the transfer process, the recording medium P passes through the position of the transfer unit 7 and then reaches the fixing device 20 through the conveyance path. The recording medium P that has reached the fixing device 20 is fed between the fixing belt 21 and the pressure roller 31, and the image is fixed by the heat received from the fixing belt 21 and the pressure received from both members 21 and 24. The The recording medium P on which the image is fixed is delivered from between the fixing belt 21 and the pressure roller 31 (a nip portion), and then discharged from the image forming apparatus main body 1.
Thus, a series of image forming processes is completed.

Next, the configuration and operation of the fixing device 20 installed in the image forming apparatus main body 1 will be described in detail with reference to FIGS.
FIG. 2 is a configuration diagram showing the fixing device 20. FIG. 3 is an enlarged view showing the cam 48 installed in the fixing device 20 of FIG. FIG. 4 is a graph showing the relationship between the rotational position of the cam 48, the cam position (distance from the center axis), and the current value of the drive motor that rotationally drives the cam 48.

As shown in FIG. 2, the fixing device 20 includes a fixing belt 21, roller members 22 and 23, a pressure roller 31, variable means 45 to 48, 52 and 53, and the like.
Here, the fixing belt 21 as a fixing member is an endless belt that runs in the clockwise direction in FIG. 2, and is stretched and supported by two roller members 22 and 23. One of the two roller members 22, 23 is in pressure contact with the pressure roller 31 via the fixing belt 21, and a heater 24 (heat source) is fixed inside the other roller member 23. ing. The fixing belt 21 is a multilayer structure in which an elastic layer and a release layer are sequentially laminated on a base layer. The fixing belt 21 is in pressure contact with a pressure roller 31 as a pressure member to form a nip portion.

As the elastic layer of the fixing belt 21, an elastic material such as fluorine rubber, silicone rubber, and foamable silicone rubber can be used. In particular, when foamed rubber is used as the elastic layer, a sufficient nip amount can be obtained at the nip portion.
As the release layer of the fixing belt 21, PFA (tetrafluoroethylene bar fluoroalkyl vinyl ether copolymer resin), polyimide, polyetherimide, PES (polyether sulfide), or the like can be used. By providing the release layer 24 on the surface layer of the fixing belt 21, the releasability (peelability) with respect to the toner T (toner image) is secured.

  One roller member 22 is formed by forming an elastic layer made of foam rubber having heat insulation on a cored bar. As a result, a decrease in temperature of the fixing belt 21 can be reduced, and a sufficient nip amount can be secured at the nip portion even if the roller member 22 has a small diameter.

The other roller member 23 is a cylindrical body formed of a metal material having good thermal conductivity.
The heater 24 provided in the roller member 23 is a rod-shaped halogen heater, and both ends thereof are fixed to the side plate of the fixing device 20. The fixing belt 21 is heated via the roller member 23 by the heater 24 whose output is controlled by the power supply unit of the apparatus main body 1, and heat is applied to the toner image T on the recording medium P from the surface thereof. The output control of the heater 24 is performed based on the detection result of the belt surface temperature by the thermopile 41 facing the surface of the fixing belt 21. Further, the temperature of the fixing belt 21 (fixing temperature) can be set to a desired temperature by such output control of the heater 24.

  The pressure roller 31 as a pressure member mainly includes a cored bar and an elastic layer formed on the outer peripheral surface of the cored bar via an adhesive layer. The elastic layer of the pressure roller 31 can be formed of a material such as fluorine rubber, silicone rubber, or foamable silicone rubber. In particular, when foamed rubber is used as the elastic layer, a sufficient nip amount can be obtained at the nip portion even if the pressure roller 31 has a small diameter. A thin release layer made of PFA or the like may be provided on the surface layer of the elastic layer.

The pressure roller 31 is pressed against the fixing belt 21 by a pressure mechanism including a lever 45 and a spring 46. In this way, a desired nip portion is formed between the pressure roller 31 and the fixing belt 21.
Here, the fixing device 20 according to the first exemplary embodiment changes the pressing position of the pressure roller 31 against the fixing belt 21 by changing the rotational position (the orientation in the rotational direction) of the cam 48, so The nip amount can be varied. This will be described in detail later.

  The heater 32 provided in the pressure roller 31 is a rod-shaped halogen heater, and both ends thereof are fixed to the side plate of the fixing device 20. The fixing belt 21 is heated via the pressure roller 31 by the heater 32 whose output is controlled by the power supply unit of the apparatus main body 1, and heat is applied to the toner image T on the recording medium P from the surface thereof. Note that the output control of the heater 32 is performed based on the detection result of the roller surface temperature by the thermistor 42 in contact with the surface of the pressure roller 31. In addition, by installing the heater 32 also on the pressure roller 31 side as described above, the temperature rise characteristic of the fixing belt 21 is improved.

A guide plate (entrance guide plate) for guiding the recording medium P conveyed toward the nip portion is disposed on the entrance side of the contact portion (a nip portion) between the fixing belt 21 and the pressure roller 31. Has been. A guide plate (exit guide plate) for guiding the recording medium P sent from the nip portion is disposed on the outlet side of the nip portion.
Further, a separation claw 28 is disposed at a position facing the outer peripheral surface of the fixing belt 21 and in the vicinity of the exit side of the nip portion. The separation claw 28 prevents a problem that the recording medium P after the fixing process is wound around the fixing belt 21.

The characteristic configuration and operation of the fixing device according to the first embodiment will be described in detail below.
In the fixing device 20 according to the first embodiment, the pressing force of the pressure roller 31 against the fixing belt 21 can be changed by changing the rotational position (posture in the rotational direction) of the cam 48 (by rotating the cam 48). Thus, the nip amount in the nip portion can be varied.

Specifically, referring to FIG. 2, the lever 45 that engages with a shaft portion (not shown) of the pressure roller 31 is configured to be rotatable around a central shaft 45a on one end side. A part of the lever 45 is provided with a spring 46 that urges the lever 45 downward (in a direction away from the fixing belt 21). A roller 47 that engages with the cam 48 is installed on the other end side of the lever 46.
With such a configuration, when the cam 48 is rotationally driven by the drive unit 52, the pressure roller 31 moves up and down along with the vertical movement of the lever 45, and the pressing force of the pressure roller 31 against the fixing belt 21 (nip portion). The nip amount at the time is variable.

  Here, the drive unit 52 includes a DC motor as a drive motor (drive source) controlled by the control unit 53 and a reduction gear train. That is, the pressure mechanisms 45 to 47, the cam 48, the drive unit 52 (drive motor), and the control unit 53 can change the relative pressure of the pressure roller 31 (pressure member) with respect to the fixing belt 21 (fixing member). It functions as a variable means. Note that the variable means 45 to 48, 52, and 53 rotate the cam 48 in the forward and reverse directions by the drive unit 52 (drive motor) to increase or decrease the applied pressure at the nip portion.

Then, when the cam 48 is rotationally driven, the control unit 53 detects a change in the value of the current flowing through the drive motor of the drive unit 52, and detects the rotational position (posture in the rotational direction) of the cam 48.
Here, referring to FIG. 3, on the peripheral surface of the cam 48, there are three pressure contact areas F1 to F3 corresponding to a desired variable pressure and three pressure contact areas adjacent to each other in the rotation direction. Transition regions R1 to R3 are formed.

Specifically, the first pressure contact region F1 of the cam 48 is brought into contact with the lever 45 (roller 47) when the applied pressure in the nip portion is reduced (depressurized). When the fixing process is not performed, the controller 53 controls the first pressure contact area F1 to contact the lever 45 (in this state, the rotation of the drive motor is stopped). As a result, even if an elastic layer made of foamed rubber is provided on the fixing belt 21 or the pressure roller 31, a large load is not always applied to the elastic layer, and hardness reduction, bubble breakage, and compression set of the elastic layer are suppressed. be able to.
The second pressure contact region F2 of the cam 48 is brought into contact with the lever 45 (roller 47) when the pressure applied at the nip portion is set to a normal value. When the fixing process is performed on the recording medium P having a normal thickness (paper thickness), the control unit 53 controls the second pressure contact area F2 to contact the lever 45.
The third pressure contact region F3 of the cam 48 is brought into contact with the lever 45 (roller 47) when the pressing force at the nip portion is higher than the normal value. When the fixing process is performed on the recording medium P (thick paper) that is thicker than usual, the control unit 53 controls the second pressure contact area F3 to contact the lever 45. As described above, by optimizing the nip amount by varying the pressing force in the nip portion according to the paper type (paper thickness) of the recording medium P, it is possible to always obtain a good fixing property.

  Here, the first transition region R1 from the first pressure contact region F1 to the second pressure contact region F2, the second transition region R2 from the second pressure contact region F2 to the third pressure contact region F3, The third transition region R3 extending from the third pressure contact region F3 to the first pressure contact region F1 is formed such that the distance from the rotation center axis of the cam 48 varies greatly as the cam 48 rotates. ing. That is, the peripheral surface of the cam 48 is formed as shown in the upper diagram of FIG. 4, the horizontal axis indicates the rotational position of the cam 48, and the vertical axis indicates the cam position (the distance from the rotation center axis of the cam 48 to the peripheral surface).

When the cam 48 formed in this way is rotated in the forward and reverse directions, the value of the current flowing through the drive motor (DC motor) varies as shown in the lower diagram of FIG.
Specifically, the cam 48 is rotated in the forward direction (in the direction of the arrow CCW in FIG. 3 and in the press-contact direction rotation region in FIG. 4) to move from the first press-contact region F1 to the second press-contact region F2. When this occurs (when the first transition region R1 has been reached), the distance from the rotation center axis of the cam 48 to the peripheral surface suddenly increases, so the load on the drive motor increases rapidly and the drive motor The current value increases dramatically. Similarly, when the cam 48 is further rotated in the forward direction to shift from the second pressure contact region F2 to the third pressure contact region F3 (when the second transition region R2 has been reached). Since the distance from the rotation center axis of the cam 48 to the peripheral surface suddenly increases, the current value of the drive motor increases drastically.
On the other hand, the cam 48 is rotated in the reverse direction (in the direction of arrow CW in FIG. 3 and in the pressure release direction rotation region in FIG. 4) to move from the third pressure contact region F3 to the second pressure contact region F2. When this occurs (when the second transition region R2 has been reached), the distance from the rotation center axis of the cam 48 to the peripheral surface is abruptly reduced, so the load on the drive motor is drastically reduced and the drive motor The current value of drastically decreases. Similarly, when the cam 48 is further rotated in the reverse direction to shift from the second pressure contact region F2 to the first pressure contact region F1 (when the first transition region R1 has been reached). Since the distance from the rotation center axis of the cam 48 to the peripheral surface is drastically reduced, the current value of the drive motor is drastically reduced.
Further, when the cam 48 is rotated in the reverse direction to shift from the first pressure contact region F1 to the third pressure contact region F3 (when the third transition region R3 has been reached), the cam 48 is used. Since the distance from the rotation center axis to the peripheral surface suddenly increases, the current value of the drive motor increases drastically.

As described above, in the first embodiment, when the applied pressure at the nip portion is varied (when the cam 48 is rotationally driven to reach the transition regions R1 to R3), the current value of the drive motor greatly varies. Therefore, it is possible to reliably detect fluctuations in the current value of the drive motor and to detect the rotational position of the cam 48 (pressure contact regions F1 to F3) with high accuracy. That is, without using an optical sensor or the like, the rotational position of the cam 48 can be grasped accurately and simply, and the applied pressure can be optimized at the nip portion.
In the first embodiment, the configuration is such that the applied pressure at the nip portion is reduced in the first pressure contact region F1 (so that a small pressure is applied), but the nip is formed in the first pressure contact region F1. It is also possible to configure so that the pressing force at the part becomes zero (so that the pressing force is released).

Here, in the first embodiment, the first print time (the time for forming one output image) in the image forming apparatus is T1, and the recording medium P is nipped after the conveyance of the recording medium P is started. Rotation drive time T of the cam 48 for moving to any one of the three pressure contact areas F1 to F3 when the time to reach the part is T2,
T ≦ T1-T2
To satisfy the relationship.
Thereby, the variable operation of the pressurizing force by the variable means is surely completed from the start of the printing operation until the recording medium P reaches the nip portion, and the effect of the above-described variable operation of the pressurizing force is certain. Become a thing.

Finally, the operation of the fixing device 20 configured as described above will be briefly described.
When the power switch of the apparatus main body 1 is turned on, power is supplied to the heaters 24 and 32, and rotation driving of the fixing belt 21 and the pressure roller 31 in the direction of the arrow in FIG.
Thereafter, the recording medium P is fed from the paper feeding units 12 to 14, and an unfixed image is carried on the recording medium P by the image forming unit 4. The recording medium P carrying the unfixed image T (toner image) is conveyed while being guided by the guide plate, and is fed into the nip portion of the fixing belt 21 and the pressure roller 31 that are in a pressure contact state. At this time, the nip amount (pressing force) of the nip portion is optimized by the variable means 45 to 48, 52, 53.
Then, the toner image T is fixed on the surface of the recording medium P by the heating by the fixing belt 21 and the pressure applied by the fixing belt 21 and the pressure roller 31. Thereafter, the recording medium P sent out from the nip portion is discharged out of the apparatus through a paper discharge path.

  As described above, in the first embodiment, the cam 48 is rotated to change the relative pressure of the pressure roller 31 (pressure member) with respect to the fixing belt 21 (fixing member). Because the current value of the drive motor that rotates the cam 48 is detected, the variable pressing force can be grasped accurately and easily, and the pressing force is optimized at the nip portion, and good fixing performance is stably achieved. Can be secured.

Embodiment 2. FIG.
The second embodiment of the present invention will be described in detail with reference to FIG.
FIG. 5 is an overall configuration diagram illustrating the image forming apparatus according to the second embodiment. The fixing device according to the second embodiment is different from that according to the first embodiment in which the fixing device is installed in the color image forming apparatus.

  In FIG. 5, reference numeral 1 denotes a main body of a tandem type color copier as an image forming apparatus, and 4Y, 4M, 4C, and 4BK form toner images of respective colors (yellow, magenta, cyan, and black) on each photosensitive drum 5. 9 is a registration roller that adjusts the conveyance timing of the recording medium P, and 15 is a toner image formed on the photosensitive drum 5 of each of the image forming sections 4Y, 4M, 4C, and 4BK. A transfer bias roller (primary transfer bias roller) 16 for transferring images in an overlapping manner, 16 is an intermediate transfer belt cleaning unit for cleaning the intermediate transfer belt 17, 17 is an intermediate transfer belt for transferring a plurality of color toner images, and 18 is an intermediate transfer belt. A secondary transfer bias roller 20 for transferring the color toner image on the transfer belt 17 onto the recording medium P, fixes the toner image (unfixed image) on the recording medium P. Chakusochi, show a.

A charging unit 54 charges the photosensitive drums 5 of the image forming units 4Y, 4M, 4C, and 4BK, and 55 is formed on the photosensitive drums 5 of the image forming units 4Y, 4M, 4C, and 4BK. A developing unit 56 that develops the electrostatic latent image, and a cleaning unit 56 that collects untransferred toner on the photosensitive drums 5 of the image forming units 4Y, 4M, 4C, and 4BK.
Here, the fixing device 20 in the second embodiment is configured and operates in the same manner as in the first embodiment. That is, in the fixing device 20 according to the second embodiment, as in the first embodiment, the cam 48 is rotated to change the relative pressure of the pressure roller 31 with respect to the fixing belt 21. The current value of the drive motor that rotationally drives the cam 48 is detected.

Hereinafter, an operation during normal color image formation in the image forming apparatus according to the second embodiment will be described.
First, the document D is transported from the document table in the direction of the arrow in the drawing by the transport rollers of the document transport unit 10 and placed on the contact glass of the document reading unit 2. Then, the document reading unit 2 optically reads the image information of the document D placed on the contact glass.

  Specifically, the document reading unit 2 scans the image of the document D on the contact glass while irradiating light emitted from an illumination lamp. Then, the light reflected by the document D is imaged on the color sensor via the mirror group and the lens. The color image information of the document D is read for each RGB (red, green, blue) color separation light by the color sensor, and then converted into an electrical image signal. Further, color conversion processing, color correction processing, spatial frequency correction processing, and the like are performed by the image processing unit based on the RGB color separation image signals to obtain yellow, magenta, cyan, and black color image information.

  Then, image information of each color of yellow, magenta, cyan, and black is transmitted to the exposure unit 3. Then, laser light (exposure light) based on the image information of each color is emitted from the exposure unit 3 toward the photosensitive drums 5 of the corresponding image forming units 4Y, 4M, 4C, and 4BK.

On the other hand, the four photosensitive drums 5 rotate in the clockwise direction in FIG. First, the surface of the photosensitive drum 5 is uniformly charged at a portion facing the charging portion 54 (a charging step). Thus, a charged potential is formed on the photosensitive drum 5. Thereafter, the surface of the charged photosensitive drum 5 reaches the irradiation position of each laser beam.
In the exposure unit 3, laser light corresponding to the image signal is emitted from four light sources corresponding to each color. Each laser beam passes through a separate optical path for each of the yellow, magenta, cyan, and black color components (this is an exposure process).

  Laser light corresponding to the yellow component is irradiated on the surface of the photosensitive drum 5 of the first image forming unit 4Y from the left side of the drawing. At this time, the yellow component laser beam is scanned in the rotation axis direction (main scanning direction) of the photosensitive drum 5 by a polygon mirror that rotates at high speed. Thus, an electrostatic latent image corresponding to the yellow component is formed on the photosensitive drum 5 charged by the charging unit 54.

  Similarly, the laser beam corresponding to the magenta component is irradiated onto the surface of the photosensitive drum 5 of the second image forming unit 4M from the left side of the paper, and an electrostatic latent image corresponding to the magenta component is formed. The cyan component laser light is applied to the surface of the photoconductive drum 5 of the third image forming unit 4C from the left side of the drawing to form a cyan component electrostatic latent image. The black component laser light is applied to the surface of the photosensitive drum 5 of the fourth image forming unit 4BK from the left side of the paper, thereby forming an electrostatic latent image of the black component.

Thereafter, the surface of the photosensitive drum 5 on which the electrostatic latent image of each color is formed reaches a position facing the developing unit 55. Then, toner of each color is supplied from each developing unit 55 onto the photosensitive drum 5, and the latent image on the photosensitive drum 5 is developed (this is a developing process).
Thereafter, the surface of the photosensitive drum 5 after the development process reaches a portion facing the intermediate transfer belt 17. Here, a transfer bias roller 15 is installed at each facing portion so as to contact the inner peripheral surface of the intermediate transfer belt 17. Then, the toner images of the respective colors formed on the photosensitive drums 5 of the respective image forming units 4Y, 4M, 4C, and 4BK are sequentially superimposed and transferred onto the intermediate transfer belt 17 at the position of the transfer bias roller 15. (This is a primary transfer step.)

Then, the surface of the photosensitive drum 5 after the transfer process reaches a position facing the cleaning unit 56. Then, the untransferred toner remaining on the photosensitive drum 5 is collected by the cleaning unit 56 (this is a cleaning process).
Thereafter, the surface of the photosensitive drum 5 passes through a static elimination unit (not shown), and a series of image forming processes on the photosensitive drum 5 is completed.

On the other hand, the intermediate transfer belt 17 onto which the toners of the respective colors formed by the image forming units 4Y, 4M, 4C, and 4BK are transferred (carrying) are run in the clockwise direction in the drawing and the secondary transfer bias roller 18 is transferred. Reach the opposite position. Then, a color toner image carried on the intermediate transfer belt 17 is transferred onto the recording medium P at a position facing the secondary transfer bias roller 18 (secondary transfer step).
Thereafter, the surface of the intermediate transfer belt 17 reaches the position of the intermediate transfer belt cleaning unit 16. Then, the untransferred toner adhered on the intermediate transfer belt 17 is collected by the intermediate transfer belt cleaning unit 16, and a series of transfer processes in the intermediate transfer belt 17 is completed.

Here, the recording medium P conveyed between the intermediate transfer belt 17 and the secondary transfer bias roller 18 (secondary transfer nip) passes from the paper feeding units 12 to 14 through the registration rollers 9 and the like. It has been transported.
Specifically, the recording medium P fed by the paper feeding roller from the paper feeding units 12 to 14 that store the recording medium P is guided to the registration roller 9 after passing through the conveyance guide. The recording medium P that has reached the registration roller 9 is conveyed toward the secondary transfer nip at the same timing.

Then, the recording medium P on which the full-color image is transferred is guided to the fixing device 20 by the transport belt. In the fixing device 20, a color image (toner) is fixed on the recording medium P at the nip between the fixing belt 21 and the pressure roller 31.
Then, the recording medium P after the fixing step is discharged as an output image outside the apparatus main body 1 by a paper discharge roller, and a series of image forming processes is completed.

  As described above, also in the second embodiment, as in the first embodiment, the cam 48 is rotated and the pressure roller 31 (pressure member) is relative to the fixing belt 21 (fixing member). Since the current value of the drive motor that rotationally drives the cam 48 is detected when changing the general applied pressure, the variable applied pressure is accurately and easily grasped, and the applied pressure is optimized at the nip portion. And good fixing properties can be secured stably.

In each of the above embodiments, the present invention is applied to a heater lamp heating type fixing device. However, the present invention can naturally be applied to another type of fixing device such as an electromagnetic induction heating method. . In this case, the same effects as those of the above embodiments can be obtained.
In each of the above embodiments, the present invention is applied to a fixing device using a fixing belt as a fixing member and a pressure roller as a pressure member. However, the present invention is applied to a fixing device using a fixing roller as a fixing member. The present invention can also be applied to this. The present invention can also be applied to a fixing device using a fixing belt as a fixing member and a pressure belt as a pressure member. The present invention can also be applied to a fixing device in which a pad is provided in a fixing member such as a fixing sleeve to form a nip portion at a contact position with the pressure member. Furthermore, the present invention can be applied to a fixing device in which a plurality of nip portions are formed between the fixing member and the pressure member.
In each of the embodiments described above, the pressure member 31 is pressed against the fixing member 21 to form a nip portion between the two members. However, the fixing member 21 is pressed against the pressure member 31 to be between the two members. A nip portion can also be formed. Also in this case, the variable means varies the relative pressure of the pressure member 31 with respect to the fixing member 21 and detects the current value of the drive motor that rotationally drives the cam, so that the same as in each of the above embodiments. An effect can be obtained.

  It should be noted that the present invention is not limited to the above-described embodiments, and within the scope of the technical idea of the present invention, the embodiments can be modified as appropriate in addition to those suggested in the embodiments. Is clear. In addition, the number, position, shape, and the like of the constituent members are not limited to the above embodiments, and can be set to a number, position, shape, and the like that are suitable for carrying out the present invention.

1 is an overall configuration diagram illustrating an image forming apparatus according to Embodiment 1 of the present invention. FIG. 2 is a configuration diagram illustrating a fixing device installed in the image forming apparatus of FIG. 1. FIG. 3 is an enlarged view showing a cam installed in the fixing device of FIG. 2. It is a graph which shows the relationship between the rotation position of a cam, the cam position, and the electric current value of a drive motor. It is a whole block diagram which shows the image forming apparatus in Embodiment 2 of this invention.

Explanation of symbols

1 image forming apparatus body (apparatus body),
20 fixing device,
21 fixing belt (fixing member),
22, 23 Roller member,
24, 32 heater,
31 Pressure roller (pressure member),
45 levers,
48 cams,
F1-F3 pressure contact area, R1-R3 transition area, P recording medium.

Claims (8)

A fixing member that heats and melts the toner image;
A pressure member that presses against the fixing member to form a nip portion;
Variable means for changing the relative pressing force of the pressing member with respect to the fixing member by changing the rotational position of the cam;
A drive motor that rotationally drives the cam;
A fixing device that detects a rotational position of the cam by detecting a change in a current value flowing through the drive motor when the cam is rotationally driven. The cam includes a plurality of pressure contact areas corresponding to the desired pressure force to be varied and a plurality of transition areas for shifting to the pressure contact areas adjacent to each other in the rotation direction,
2. The fixing device according to claim 1, wherein the plurality of transition regions are formed such that a distance from a rotation center axis of the cam greatly varies with rotation of the cam.   The fixing device according to claim 2, wherein at least one pressure contact region of the plurality of pressure contact regions sets the applied pressure to zero. When the first print time in the image forming apparatus is T1, and the time from the start of conveyance of the recording medium until the recording medium reaches the nip portion is T2, any one of the plurality of pressure contact areas is pressed. The rotational drive time T of the cam for moving to the area is
T ≦ T1-T2
The fixing device according to claim 2, wherein the following relationship is satisfied.   5. The fixing device according to claim 1, wherein the variable unit is configured to increase or decrease the pressing force by rotating the cam in a forward or reverse direction by the drive motor. .   The fixing device according to claim 1, wherein the drive motor is a DC motor.   The fixing device according to claim 1, wherein at least one of the fixing member and the pressure member includes an elastic layer made of foamed rubber.   An image forming apparatus comprising the fixing device according to claim 1.

Images