JP2002040863A - Fixing device and image forming device using it - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device which variably controls the glossiness of an image fixed on a form with a high precision. SOLUTION: A pressure lever 34 is attached to a supporting cylinder part 31 of a lower fixing roll 23. An operating plate 38 is attached to one end of the pressure lever 34 with a tension spring 37 between them. The operating plate 38 is vertically displaced in accordance with rotation of an eccentric cam 40. The pressure lever 34 is displaced by this displacement to change a fixing pressure. A position detection sensor 45 detects the position of the operating plate 38 by the angular position of the eccentric cam 40. A driving signal C to be sent to a motor 49 from a control part 44 is adjusted on the basis of the detection result of the position detection sensor 45, and the position of the operating plate 38 is changed to control the fixing pressure. Since the position of the operating plate 38 is detected, the fixing pressure can be variably controlled with a high precision on the basis of the detection result.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a fixing device capable of variably controlling the glossiness of an image fixed on a sheet and an image forming apparatus using the fixing device.

[0002]

2. Description of the Related Art Conventionally, an image forming apparatus including a fixing device including a pair of fixing rollers is known. In this type of image forming apparatus, the fixing roller pair is pressed against a predetermined fixing pressure,
For example, both are heated to a predetermined fixing temperature. The paper on which the toner image has been transferred by the photosensitive drum passes between these fixing roller pairs, whereby the toner particles are melted and fixed. At this time, the fixed image has a certain glossiness.

[0003]

However, there is a difference in the degree of gloss perceived by the user as being easy to see. Also, the glossiness is preferably low for a character image and high for a color image. In order to variably control the glossiness, it is conceivable to change the rotation speed of the fixing roller pair. However, it is difficult to change the rotation speed in a plurality of steps. In particular, in a tandem-type image forming apparatus having a plurality of image forming units along the sheet conveyance path, the speed of the entire system of the image forming apparatus must be changed.

[0004] It is also possible to variably control the glossiness by changing the fixing pressure. However, the relative displacement between the pair of fixing rollers is as small as about 0.2 mm to 0.5 mm. If the relative displacement is directly detected to change the fixing pressure, the error increases. Therefore, it may not be possible to form an image with a gloss level desired by the user. The present invention has been made under such a background, and an object of the present invention is to provide a fixing device capable of accurately and variably controlling the glossiness of an image and an image forming apparatus using the fixing device.

[0005]

Means for Solving the Problems and Effects of the Invention In order to achieve the above object, the invention according to claim 1 is to heat and press a sheet carrying an unfixed toner image, which is pressed against each other at a predetermined fixing pressure. A pair of fixing rollers for fixing the toner image to the sheet by passing the toner image onto the sheet, and an initial position where the fixing pressure is minimized by being connected to at least one of the pair of fixing rollers via an elastic member. A fixing device comprising: an operating member capable of being displaced between a maximum pressing position where a pressure is maximum, and a driving mechanism for displacing the operating member between an initial position and a maximum pressing position. Device.

According to this configuration, since the operating member is connected to the fixing roller via the elastic member, it can have a large displacement width due to expansion and contraction of the elastic member. The fixing pressure is given by the restoring force generated by the elastic member. This restoring force is determined by the position of the operating member and the spring constant of the elastic member. Thus, by displacing the operating member by the driving mechanism, the fixing pressure can be variably set to a desired value. Since the operating member can take an arbitrary position within a large displacement width, the fixing pressure depending on the position of the operating member can be set with good accuracy.

[0007] A pressurizing member may be interposed between the fixing roller and the elastic member. In this case, the pressing member is swung by the displacement of the operating member, and the fixing roller is pressed against the other fixing roller. Therefore, the fixing pressure can be changed with a simple configuration. According to a second aspect of the present invention, a fixing pressure for changing the fixing pressure by controlling the driving mechanism based on a detection result of the position detecting means and a position detecting means for detecting a position of the operating member. The fixing device according to claim 1, further comprising a control unit.

The correspondence between the position of the operating member and the fixing pressure is as described above. Thus, the fixing pressure can be indirectly detected by detecting the position of the operating member. As described above, since the operating member can be displaced within a large displacement width, the fixing pressure can be detected with high accuracy. Therefore, by performing feedback control of the drive mechanism based on the detection result of the position of the operating member, the fixing pressure can be set with good accuracy.

The fixing pressure control means may control the driving mechanism based on the detection result of the thickness detecting means for detecting the thickness of the sheet. In this case, if the fixing pressure is controlled to decrease when a thin sheet is conveyed, it is possible to prevent the sheet from being wrinkled or torn due to excessive pressure. Further, the invention according to claim 3 further includes a glossiness setting means for setting the glossiness of the image, and the fixing pressure control means, based on the setting of the glossiness setting means,
3. The fixing device according to claim 2, wherein the driving mechanism is controlled.

According to this configuration, the user can set the glossiness by the glossiness setting means, and the fixing pressure is accurately controlled based on the glossiness, so that the image having the desired glossiness can be reliably formed. Can be formed. According to a fourth aspect of the present invention, the driving mechanism includes an eccentric cam for displacing the operating member according to a rotational position, and the position detecting means detects an angular position of the eccentric cam. The fixing device according to claim 2, wherein the position of the operating member is indirectly detected by the following.

In this configuration, by utilizing the fact that there is a correspondence between the angular position of the eccentric cam and the position of the operating member, the position of the operating member is indirectly detected by detecting the angular position of the eccentric cam. You. Thus, the position of the operating member can be detected with a simple configuration. According to a fifth aspect of the present invention, an unfixed toner image is formed on a sheet by developing the electrostatic latent image formed on the surface of the photoreceptor into a toner image and transferring the toner image to a sheet. 5. An image forming unit, and a device for fixing the unfixed toner image on a sheet.
An image forming apparatus comprising: the fixing device according to any one of the above.

According to this configuration, it is possible to provide an image forming apparatus using the fixing device having the above-described effects.

[0013]

Embodiments of the present invention will be specifically described below with reference to the drawings. FIG. 1 is a schematic sectional view showing an internal configuration of an image forming apparatus 1 according to an embodiment of the present invention. This image forming apparatus 1 has a black
Four image forming units 2B, 2M, 2C, and 2 for forming monochromatic images of magenta, cyan, and yellow, respectively.
Y has a so-called tandem type structure in which the sheets Y are arranged in a line in this order from the upstream side in the sheet conveying direction along a linear conveying path formed by the sheet conveying mechanism 3 for conveying the sheet P. .

Image forming units 2B, 2M, 2C, 2Y
Are provided with cylindrical photoconductors 4B, 4M, 4C, and 4Y, respectively, and are arranged in parallel with each other with their axes extending in a horizontal direction orthogonal to the paper transport direction.
The image forming units 2B, 2M, 2C, and 2Y
B, 4M, 4C, and 4Y, respectively, form black, magenta, cyan, and yellow single-color toner images. The toner images are guided to a position facing the paper transport mechanism 3 by rotation about the axis of the photoconductor. I will black,
The magenta, cyan, and yellow toner images are sequentially transferred onto the surface of the paper P while the paper transport mechanism 3 is transporting the paper P.

The paper transport mechanism 3 includes a driving roller 5 disposed further downstream than the most downstream image forming unit 2Y in the paper transport direction, and a further upstream from the uppermost stream image forming unit 2B in the paper transport direction. Roller 6, a driving roller 5 and a driven roller 6
Endless conveyor belt 7 wound around
And an auxiliary roller 8 for applying a tension to the sheet to suppress bending. With this configuration, when a driving force from a motor (not shown) is applied to the driving roller 5 to rotate the driving roller 5, the transport belt 7 rotates counterclockwise in FIG. The sheet P on which the toner image is to be transferred is transported linearly in the direction of arrow A by the rotation of the transport belt 7 while being carried on the upper surface of the transport belt 7.

At positions facing the photoconductors 4B, 4M, 4C, and 4Y from below, the upper portion of the transport belt 7 is sandwiched therebetween.
Transfer roller 9B for black, transfer roller 9 for magenta
M, cyan transfer roller 9C and yellow transfer roller 9Y are arranged. Each transfer roller 9B,
9M, 9C and 9Y press the conveyor belt 7 against the photoconductors 4B, 4M, 4C and 4Y from below, and transfer the toner images on the photoconductors 4B, 4M, 4C and 4Y to the paper P. It has a function.

Below the paper transport mechanism 3, a paper feed tray 10 capable of stacking and storing a plurality of papers P is disposed. The paper feed tray 10 includes a paper feed roller 12 for feeding the paper P from the paper feed tray 10 to the transport path 11 one by one. The paper P sent to the transport path 11 via the transport roller pair 13 by the rotation of the paper feed roller 12 is transported toward the registration roller pair 16 by the transport roller pairs 14 and 15. The registration roller pair 16 is connected to the paper transport mechanism 3 with respect to the transport direction of the paper P.
After stopping the transported paper P once, the image forming units 2B, 2M, 2C,
The sheet P is sent out onto the conveyor belt 7 in synchronization with the toner image forming operation in 2Y.

Each of the image forming units 2B, 2M, 2C, 2
Above Y, photoconductors 4B, 4M, 4C, 4Y
Laser scanning unit 17B, magenta laser scanning unit 17M, cyan laser scanning unit 17C, and yellow laser scanning unit 17Y for irradiating a laser beam to the laser beam.
Is arranged. The image forming apparatus 1 is connected to an external device (not shown) such as a microcomputer, for example. Image data input from this external device is
After being decomposed into color image data of each color component of black, magenta, cyan, and yellow, it is provided to laser scanning units 17B, 17M, 17C, and 17Y corresponding to each color.

The laser scanning units 17B, 17M, 17C, 1
7Y has a laser beam (not shown), a polygon mirror, a reflecting mirror, and the like. When color image data representing the densities of the respective colors of black, magenta, cyan, and yellow is input, based on the color image data, Modulated laser beams Lb, Lm, Lc, Ly
Are emitted toward the photoconductors 4B, 4M, 4C, and 4Y, respectively. The photoconductor 4B provided in the black image forming unit 2B is moved at a constant speed in the direction of the arrow (FIG. 1) during image formation.
(Clockwise direction in FIG. 3). Photoconductor 4B
A main charger 18, a developing device 19, and a cleaner 20 are arranged in this order along the rotation direction. The laser beam Lb incident from the black laser scanning unit 17B is applied to the surface of the photoconductor 4B between the main charger 18 and the developing device 19.

The photosensitive member 4B is uniformly charged by the discharge of the main charger 18, and is then exposed to the laser beam Lb incident from the black laser scanning unit 17B. Thus, a so-called electrostatic latent image is formed on the surface of the photoconductor 4B. Photoconductor 4 on which electrostatic latent image is formed
Next, the surface of B is developed with black toner by the black developing device 19. When the photoconductor 4B is further rotated, the black toner image formed on the surface of the photoconductor 4B faces the paper transport mechanism 3.

On the other hand, the registration roller pair 16 is driven to rotate in synchronization with the toner image facing the paper transport mechanism 3, and the paper P is fed by the transport belt 7. A predetermined transfer voltage is applied to the black transfer roller 9B, which is disposed at a position facing the photoconductor 4B from below with the upper portion of the transport belt 7 interposed therebetween. Thus, the black toner on the surface of the photoconductor 4B is attracted to the black transfer roller 9B and is transferred to the upper surface of the sheet P. The toner remaining on the surface of the photoconductor 4B after the transfer of the toner image is collected by the cleaner 20.

The paper P on which the black toner image has been transferred in this manner is transported by the transport belt 7 to the image forming unit 2.
It is conveyed toward M, 2C, and 2Y. The image forming units 2M, 2C, and 2Y are configured similarly to the above-described black image forming unit 2B, and apply magenta, cyan, and yellow toner images to the photoconductors 4M, 4C, and 4Y in accordance with the conveyance timing of the paper P. Each of the single-color toner images formed thereon is sequentially transferred onto the paper P in an overlapping manner.

As described above, the paper P on which the toner images of the respective colors are transferred in an overlapping manner is separated from the transport belt 7 and
It is guided to the fixing unit 21. In the fixing unit 21,
Fixing rollers 22 and 23 are provided as a pair of fixing rollers. The upper roller of the pair of fixing rollers 22 and 23 is heated to a predetermined fixing temperature by, for example, a heater (not shown), and is a heat roller for melting and fixing the toner attached to the sheet P. Is the upper fixing roller 22. The lower roller is, for example, a fixing upper roller 2
Reference numeral 2 denotes a lower fixing roller 23 as a pressure roller pressed against a predetermined fixing pressure.

As a result, the sheet P conveyed toward the fixing unit 21 is sent out of the fixing unit 21 by the discharge roller pair 24 while being sandwiched between the upper fixing roller 22 and the lower fixing roller 23. At this time, the toner on the sheet P is melted by the upper fixing roller 22, and the melted toner is fixed on the sheet P by pressure. The sheet P after the fixing process is discharged to a discharge unit 2 by discharge roller pairs 25 and 26.
It is discharged to 7. The lower fixing roller 23 is a fixing upper roller 2
It may be heated by a heater as in the case of 2.

FIG. 2 is a perspective view of the fixing unit 21 as viewed obliquely from above. The fixing unit 21 includes a fixing upper roller 22 and a fixing lower roller 23 in a housing 28 of the main body.
have. However, the front left side in FIG.
The right back side is the back. The upper fixing roller 22 has, for example, a cylindrical shape and extends in a horizontal direction orthogonal to the sheet conveying direction B, and has a support cylinder portion 29 formed at both ends thereof. At the center of the upper fixing roller 22, a heater (not shown) is provided with both ends supported. Support tube 29
Is rotatably held by opposite front and rear sides of the housing 28. At one end 29a of the support cylinder 29,
A fixing upper roller gear (not shown) is connected. The upper fixing roller gear is connected to a motor (not shown) via, for example, a plurality of gears (not shown). When the image forming apparatus 1 is operated, the motor is driven to move the upper fixing roller 22 in the transport direction C. To rotate.

The lower fixing roller 23 has, for example, a cylindrical shape and extends parallel to the upper fixing roller 22, and has a support cylinder 31 formed at both ends thereof. A heater (not shown) is provided at the center position of the lower fixing roller 23 with both ends supported. Both ends of the support cylinder portion 31 are inserted into insertion holes 32 formed on both front and rear opposing sides of the housing 28, and are held rotatably. The inner diameter of the insertion hole 32 is formed slightly larger than the outer diameter of the support cylinder 31, and the support cylinder 31 can be slightly displaced in the radial direction.

The outer peripheral surface of the upper fixing roller 22 and the lower fixing roller 23 are in pressure contact with each other at a nip position 33. During the operation of the fixing unit 21, the lower fixing roller 23 receives the nip pressure at the nip position 33 and rotates in the transport direction D with the rotation of the upper fixing roller 22. A lower fixing roller gear that meshes with the fixing roller gear is connected to one end of the supporting cylindrical portion 31 of the lower fixing roller 23, and the supporting cylindrical portion 29 of the upper fixing roller 22 is driven by the motor.
May be integrally rotated.

Both ends of the lower fixing roller 23 and the housing 28
Between the pressure levers 34, 3
4 are interposed. The rotation shaft 31 is inserted through each of the pressure levers 34, 34. In addition, each pressure lever 3
One end of each of the pressurizing levers 34 and 34 is held by supporting shafts 35 and 35 connected to the housing 28, and each of the pressing levers 34 and 34 can swing about the supporting shafts 35 and 35, respectively. I have. Connection holes 36, 36 are formed at the other ends of the pressure levers 34, 34, respectively. Each connection hole 36, 36 has a hook portion 37a at one end of a tension spring 37, 37 as an elastic member. , 37a are hooked.

On the inner surfaces of the front and rear sides of the housing 28 above the pressure levers 34, 34, operating plates 38, 38 as box-shaped operating members are respectively mounted so as to be vertically displaceable. On the lower surface of each operation plate 38, 38,
Each of the connection holes 39, 39 is formed, and each of the connection holes 39, 39 has a corresponding tension spring 37, 37, respectively.
Hook portions 37b, 37b at the other end are hooked. Eccentric cams 40, 40 are disposed inside the respective operation plates 38, 38, and a rotating shaft 41 is connected to the eccentric cams 40, 40. The rotating shaft 41 has both ends rotatably held by the front and rear sides of the housing 28. Referring to FIG. 3, a gear mechanism 46 is connected to one end of rotating shaft 41. The gear mechanism 46 includes a motor 47 whose drive is controlled by a control unit (not shown).
When the motor 47 rotates, the eccentric cams 40 and 40 are integrally rotated.

The two eccentric cams 40, 40, the rotating shaft 41, the gear mechanism 46, and the motor 47 form a drive mechanism for displacing the operation plate 38. FIG. 3A shows a state in which the operation plate 38 is at the initial position, and FIG. 3B shows a state in which the operation plate 38 is at the maximum pressing position. FIG. 4 is a block diagram showing a control circuit configuration of a portion related to the present invention in the image forming apparatus 1. In FIG. 3A, the eccentric cam 40 has an operating plate 38 at a portion where its diameter is minimum.
The operation plate 38 is located at the initial position.

For example, on the upper surface of the main body of the image forming apparatus 1,
An operation unit 42 for performing various operations is arranged. The operation unit 42 includes a glossiness selection button 43 as a glossiness setting means for, for example, selecting the glossiness of an image recorded on a sheet stepwise. Further, inside the image forming apparatus 1, there is provided a control unit 44 as a fixing pressure control unit constituted by a microcomputer or the like. When the user operates the glossiness selection button 43 to set a desired glossiness, the control unit 44 drives the motor 47 in accordance with the set glossiness to change the angular position of the eccentric cam 40 and operate the motor. The plate 38 is guided to a position corresponding to the set glossiness. When the operation plate 38 moves up and down, the tension spring 37 expands and contracts accordingly, so that the pressure at which the lower fixing roller 23 is pressed against the upper fixing roller 22, that is, the fixing pressure, depends on the position of the operation plate 38 and the spring of the tension spring 37. It is determined by the coefficient. Specifically, when the operating plate 38 is raised, the fixing pressure increases, and when the operating plate 38 is lowered, the fixing pressure decreases.

The expansion and contraction of the tension spring 37 allows the operating plate 38 to move up and down within a large displacement range. Therefore, the fixing pressure can be set with good accuracy by determining the vertical position of the operation plate 38.
The position detection sensor 45 as a position detection unit detects the angular position of the rotation shaft 41 of the eccentric cam 40,
The vertical position of the operation plate 38 is indirectly detected. The control unit 4 sets the detection value of the position detection sensor 45 to a value corresponding to the gloss level set by the gloss level selection button 43.
Reference numeral 4 designates a drive signal C to be supplied to the motor 47. That is, based on the output of the position detection sensor 45, the motor 47
Is feedback-controlled, whereby the operation plate 38 is guided to a position corresponding to the set glossiness. If the set glossiness is high, the operating plate 38 is guided to a relatively upper position to increase the fixing pressure. Conversely, if the set gloss level is low, to lower the fixing pressure,
The operating plate 38 is guided to a relatively low position. In this way, a fixing pressure corresponding to the glossiness is achieved.

As shown in FIG. 3B, the upper surface of the operating plate 38 is supported at the portion where the diameter of the eccentric cam 40 is the largest, and when the operating plate 38 is raised to the maximum pressing position, the fixing roller pair 22 The fixing pressure between 23 is maximum. When comparing FIG. 3A and FIG. 3B, the operation plate 38 has the tension spring 3.
7, the displacement amount of the operation plate 38 is larger than the displacement amount of the pressure lever 34 by the extension of the tension spring 37. Therefore, the operation plate 3
By detecting the position 8, a more accurate detection result can be obtained than when the position of the pressure lever 34 is detected, and the fixing pressure can be adjusted with higher accuracy. As a result, the glossiness of the image fixed on the paper P can be variably controlled with high accuracy.

The image forming apparatus 1 may be provided with the following control means (1) to (3) in addition to the fixing pressure control means. By combining one or more of these control means with the fixing pressure control means, the paper P
The glossiness of the image fixed to the image can be variably controlled with higher accuracy. (1) Temperature control means for changing the fixing temperature between the fixing roller pair 22 and 23. This temperature control means lowers the fixing temperature when a low glossiness is selected by the glossiness selection button 43, and raises the fixing temperature when a high glossiness is selected. (2) Rotation control means for changing the rotation speed of the fixing roller pair 22, 23. The rotation control means increases the rotation speed when a low glossiness is selected by the glossiness selection button 43, and decreases the rotation speed when a high glossiness is selected. (3) Paper control means for selecting a dedicated paper from a paper tray and feeding the selected paper. This sheet control means feeds a dedicated sheet corresponding to the glossiness selected by the glossiness selection button 43 from a paper tray.

The present invention is not limited to the contents of the above embodiment, and various modifications can be made within the scope of the claims. For example, the pressure lever 34 is not the support cylinder 31 of the lower fixing roller 23 but the upper fixing roller 2.
2 is provided on the supporting cylinder portion 29 of the
May be pressed against the lower fixing roller 23, or the fixing rollers 22 and 23 may be provided on both the support cylinders 29 and 31 to press the fixing rollers 22 and 23 against each other. In this embodiment, the upper fixing roller 22 is a heat roller and the lower fixing roller 23 is a pressure roller. However, the upper fixing roller 22 may be a pressure roller and the lower fixing roller 23 may be a heat roller.

The elastic member is not limited to the tension spring 37.
For example, a compression spring may be used. In this case, a compression spring may be provided below the pressure lever 34, and the operating member may be connected to the lower end thereof. By raising and lowering this operating member, the pressing force from the upper end of the compression spring to the pressing lever 34 can be changed, and the fixing pressure can be changed. The glossiness selection button 43 is not limited to one that is selected stepwise, and may be one that is continuously selected. In this case, since the glossiness can be arbitrarily variably controlled, the glossiness desired by the user can be achieved.

The position detecting means comprises a position detecting sensor 4
The present invention is not limited to this example. For example, a step motor, a pulse motor, or the like may be used as the motor 47 to detect the position of the operating member from the drive signal of the motor 47.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing an internal configuration of an image forming apparatus according to an embodiment of the present invention.

FIG. 2 is a perspective view of the fixing unit as viewed obliquely from above.

FIG. 3 is a schematic diagram showing an operation mode of an operation plate.

FIG. 4 is a block diagram illustrating a control circuit configuration of a portion related to the present invention in the image forming apparatus.

[Explanation of symbols]

 Reference Signs List 1 image forming apparatus 21 fixing unit (fixing device) 22 fixing upper roller 23 fixing lower roller 37 tension spring (elastic member) 38 operating plate (operating member) 41 eccentric cam 43 glossiness selection button (glossiness setting means) 44 control unit (Fixing pressure control means) 45 Position detection sensor (Position detection means) P paper

Claims (5)

[Claims] A pair of fixing rollers that are pressed against each other at a predetermined fixing pressure and fix the toner image on the sheet by passing the sheet carrying the unfixed toner image while heating and pressurizing the sheet; An operating member connected to at least one of the rollers via an elastic member and displaceable between an initial position where the fixing pressure is minimum and a maximum pressing position where the fixing pressure is maximum; And a drive mechanism for displacing the position between an initial position and a maximum pressing position. 2. A fixing device comprising: a position detecting means for detecting a position of the operating member; and a fixing pressure control means for changing the fixing pressure by controlling the driving mechanism based on a detection result of the position detecting means. The fixing device according to claim 1, wherein: 3. The image forming apparatus according to claim 2, further comprising: a gloss setting unit for setting a gloss level of the image, wherein the fixing pressure control unit controls the driving mechanism based on the setting of the gloss level setting unit. The fixing device according to claim 2, wherein: 4. The driving mechanism includes an eccentric cam for displacing the operating member in accordance with a rotational position, and the position detecting means operates indirectly by detecting an angular position of the eccentric cam. The fixing device according to claim 2, wherein a position of the member is detected. 5. An image forming section for developing an electrostatic latent image formed on the surface of a photoreceptor into a toner image and transferring the toner image to a sheet to form an unfixed toner image on the sheet. 2. A method for fixing an unfixed toner image on a sheet.
An image forming apparatus, comprising: the fixing device according to any one of (1) to (4).