JP2014219699A - Fixing device and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fixing device which can switch between a non-pressure state and a pressure-contact state without adding any mechanism or complicating the configuration, does not cause noise during switching, and can arbitrarily switch to appropriate nip width and nip pressure according to mode difference such as a paper type or a paper thickness.SOLUTION: In a lower unit 52 of a fixing device, a pressing roller unit 76 holding a pressing roller 62 is provided so as to be vertically rotatable around an axis center 75, and rotation of the pressing roller is driven by a cam 77. According to difference in height of a cam surface from a rotation center of the cam 77 and according to rotation of the cam 77 in the clockwise direction, the pressing roller 62 is put into a plurality of press-contact positions relative to a fixing roller 54 via a fixing belt 58. The non-pressure state is brought about by the rotation of the cam 77 in an opposite direction (the counterclockwise direction).

Description

  The present invention relates to a fixing device for fixing an unfixed image on a recording medium, a copier having the fixing device, a printer, a facsimile, a printing machine, a plotter, and an image forming apparatus such as a multifunction machine provided with at least one of them. .

In an image forming apparatus using toner for forming a visible image, a fixing device is provided to fix the toner image as a permanent image on a recording medium such as transfer paper.
In the fixing device, a recording medium passes through a pressure contact portion (nip portion) formed by a heated and rotating fixing roller or fixing belt and a pressure roller or pressure belt rotating and pressing with the fixing roller or fixing belt. As a result, the toner carried on the recording medium is melted and the toner image is fixed on the recording medium.
Patent Document 1 discloses a fixing device having a configuration in which the pressure roller position is displaced for the purpose of extending the life of the fixing roller.
The present invention is a mechanism in which the pressure roller position in the pressurized state and the depressurized state is changed by rotation of the eccentric cam. By rotating the eccentric cam once in a certain direction, switching from depressurization to press contact and further depressurization is performed.

In Patent Document 2, a plurality of urging means and a plurality of pressure-bonding switching cams corresponding to each arm are provided at both ends of the pressure roller, and the plurality of pressure-bonding switching cams are rotated by the rotation of the pressure-bonding release lever. The configuration is described. Depending on the position of the pressure switching cam, the arm contacts and separates from the pressing roller against the pressing force of the biasing means, and some of the pressing forces by the plurality of biasing means bias the pressure roller. This is a configuration that can be selected.
With this configuration, the pressure applied to the nip portion by the mode such as the paper type and the paper thickness is variable.

In the configuration described in Patent Document 1, the direction of the moment received by the eccentric cam shaft changes from the pressure contact to the pressure release. There was a problem that abnormal sound such as impact sound occurred on the opposite side.
To solve this problem, force is transmitted from the drive side using a damper member or a one-way clutch, but the transmission of force from the camshaft side is locked. There must be an additional mechanism that leads to up.
In the method of Patent Document 2, the configuration is complicated, and a plurality of arms, urging means, and cams are required, which inevitably increases the cost.

  The present invention has been made in view of such a current situation, and it is possible to switch between depressurization and pressure contact without adding a mechanism or complicating the configuration, and it is possible to generate abnormal noise at the time of switching. The main object of the present invention is to provide a fixing device that can arbitrarily switch an appropriate nip width and nip pressure depending on a mode such as a paper type and a paper thickness.

  In order to achieve the above object, according to the first aspect of the present invention, a recording medium holding an unfixed toner image is conveyed to a nip portion between rotating members as fixing members, and is fixed by being sandwiched and heated. In the fixing device, the pressure roller that is one rotating body has a displacement configuration that can be set at a plurality of positions with respect to the fixing roller that is the other rotating body, and both end portions of the pressure roller are respectively In the fixing device including a holding pressure lever and a cam for rotating the pressure lever to displace the pressure roller, the cam is rotated in a certain direction so that the pressure roller is rotated by the fixing roller. It has the shape which press-contacts and depressurizes by rotation of a reverse direction, It is characterized by the above-mentioned.

According to a second aspect of the present invention, in the fixing device according to the first aspect, the cam has a shape in which the cam surface height constantly increases from the center of the cam shaft in accordance with the rotation in the pressing direction. To do.
According to a third aspect of the present invention, in the fixing device according to the second aspect, at a predetermined pressure position, the cam surface height change rate in the vicinity of the cam surface contact position is 0.05 mm or less per degree. It is characterized by being.
According to a fourth aspect of the present invention, in the fixing device according to any one of the first to third aspects, the pressing device includes a biasing member that biases the pressure lever in a pressure contact direction with the fixing roller. The position of the urging member that is not in contact with the pressure lever is displaced by the rotation of the cam, and the pressure lever is rotated via the urging force of the urging member.

According to a fifth aspect of the present invention, in the fixing device according to any one of the first to fourth aspects, the cam position detecting means for detecting the position of the cam and a detection signal from the cam position detecting means. And a control means for controlling the drive source for driving the cam and displacing the position of the pressure roller in accordance with the paper type, paper thickness and mode.
According to a sixth aspect of the present invention, in the fixing device according to any one of the first to fifth aspects, an upper limit position when the cam rotates in a direction in which the pressure roller is pressed against the fixing roller is detected. Based on the cam upper limit position detecting means and the signal from the cam upper limit position detecting means, an error is lit or the cam is reversely rotated in the pressure-removing direction and the pressure roller is displaced again to a predetermined pressure contact position. It has the control means to control in this way.
According to a seventh aspect of the present invention, an image forming apparatus includes the fixing device according to any one of the first to sixth aspects.

  According to the present invention, it is possible to switch between depressurization and pressure contact with a simple configuration, and no abnormal noise or impact sound is generated at the time of switching, and appropriate depending on the mode of paper type, paper thickness, etc. Nip width and nip pressure can be arbitrarily switched. As a result, an image forming apparatus having a wide paper type compatibility can be realized.

1 is a schematic configuration diagram of a fixing device according to an embodiment of the present invention. FIG. 2 is a detailed external view of the fixing device. FIG. 3 is a schematic configuration diagram of a lower unit of the fixing device in a depressurized state in which a pressure roller is separated. 2 is a schematic configuration diagram of a lower unit of the fixing device in a state of pressure 1. FIG. 2 is a schematic configuration diagram of a lower unit of the fixing device in a state of pressure 2. FIG. It is a schematic block diagram of the lower unit which shows the state returned from the state of the pressure 1 or the pressure 2 to the decompression position. It is a figure which shows the shape of a cam. It is a figure which shows the relationship between cam surface height and a torque, (a) is a figure which shows the relationship between a cam position angle and cam surface height, (b) is a figure which shows the relationship between a cam position angle and a cam shaft moment. It is a figure which shows the relationship between cam surface height and a torque, (a) is a figure which shows the relationship between a cam position angle and cam surface height change rate, (b) is a figure which shows the relationship between a cam position angle and a cam shaft moment. . It is a figure which shows a cam position detection means, (a) is a figure which shows the sensor which detects a home position, (b) is a figure which shows a cam upper limit position detection sensor. It is a control block diagram. It is a general | schematic perspective view of a pressure roller unit. It is a perspective view which shows the principal part of the rotation structure of a pressure roller unit. It is a perspective view of an inner lever. It is a figure which shows the urging | biasing structure in the assembly | attachment of an inner lever and an outer lever. 1 is a diagram illustrating an outline of a configuration of an image forming apparatus.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
First, the outline of the configuration and operation of a tandem type color copier as an image forming apparatus in the present embodiment will be described with reference to FIG. The color copying machine 1 includes an image forming unit 1A positioned at the center of the apparatus main body, a paper feeding unit 1B positioned below the image forming unit 1A, and an image reading unit 1C positioned above the image forming unit 1A. Have.
An intermediate transfer belt 2 as a transfer body having a transfer surface extending in the horizontal direction is disposed in the image forming unit 1A, and an image of a color complementary to the color separation color is disposed on the upper surface of the intermediate transfer belt 2. The structure for forming is provided. That is, the photosensitive drums 3Y, 3M, 3C, and 3B as image carriers capable of carrying an image of complementary color toners (yellow, magenta, cyan, and black) are arranged along the transfer surface of the intermediate transfer belt 2. It is juxtaposed.

Each of the photosensitive drums 3Y, 3M, 3C, and 3B is composed of a drum that can rotate in the same counterclockwise direction, and around the charging device 4 is a charging unit that performs image forming processing in the rotation process. The optical writing device 5 as an exposure unit for forming an electrostatic latent image on the photosensitive drums 3Y, 3M, 3C, and 3B based on the image information, and the electrostatic latent images on the photosensitive drums 3 A developing device 6 as a developing means for developing with toner having the same polarity as the electrostatic latent image, a transfer bias roller 7 as a primary transfer means, an applied voltage member 15, and a cleaning device 8 are arranged. The alphabets attached to the respective symbols correspond to the colors of the toner as in the photosensitive drum 3. Each developing device 6 accommodates each color toner.
The intermediate transfer belt 2 is configured to be wound around a plurality of rollers 2A to 2C and to move in the same direction at a position facing the photosensitive drums 3Y, 3M, 3C, and 3B. A roller 2C, which is different from the rollers 2A and 2B that support the transfer surface, faces the secondary transfer device 9 with the intermediate transfer belt 2 interposed therebetween. In FIG. 16, reference numeral 10 indicates a cleaning device for the intermediate transfer belt 2.

The surface of the photosensitive drum 3Y is uniformly charged by the charging device 4Y, and an electrostatic latent image is formed on the photosensitive drum 3Y based on the image information from the image reading unit 1C. The electrostatic latent image is visualized as a toner image by a two-component (carrier and toner) developing device 6Y containing yellow toner, and the toner image is formed on the intermediate transfer belt 2 as a first transfer step. The image is attracted and transferred by the electric field generated by the voltage applied to the transfer bias roller 7Y.
The applied voltage member 15Y is provided on the upstream side of the transfer bias roller 7Y in the rotation direction of the photosensitive drum 3Y. The applied voltage member 15Y applies a voltage to the intermediate transfer belt 2 that has the same polarity as the charging polarity of the photosensitive drum 3Y and has an absolute value that is larger than the solid value, and is intermediate from the photosensitive drum 3Y before the toner image enters the transfer area. The toner is prevented from being transferred to the transfer belt 2, thereby preventing disturbance due to dust when the toner is transferred from the photosensitive drum 3 </ b> Y to the intermediate transfer belt 2.

The other photoconductor drums 3M, 3C, and 3B also form similar images only with different toner colors, and the toner images of the respective colors are sequentially transferred onto the intermediate transfer belt 2 and superimposed.
The toner remaining on the photosensitive drum 3 after the transfer is removed by the cleaning device 8, and the potential of the photosensitive drum 3 is initialized by a neutralizing lamp (not shown) after the transfer to prepare for the next image forming process.
The secondary transfer device 9 includes an intermediate transfer belt 2 that is wound around a charging drive roller 9A and a driven roller 9B, and a transfer belt 9C that moves in the same direction. By charging the transfer belt 9C with the charging drive roller 9A, it is possible to transfer a multicolor image superimposed on the intermediate transfer belt 2 or a single color image carried on a sheet 28 as a recording medium.

The paper 28 is fed from the paper feed unit 1B to the secondary transfer position. The paper feed unit 1B has a plurality of paper feed cassettes 1B1 in which papers 28 are stacked and housed, and a paper feed roller 1B2 that separates and feeds the papers 28 contained in the paper feed cassette 1B1 one by one in order from the top. A pair of conveying rollers 1B3, a pair of registration rollers 1B4 positioned upstream of the secondary transfer position, and the like.
The paper 28 fed from the paper feed cassette 1B1 is temporarily stopped by the registration roller pair 1B4, and after correcting the oblique displacement and the like, the front end of the toner image on the intermediate transfer belt 2 and a predetermined position at the front end in the transport direction are set. Are sent to the secondary transfer position by the registration roller pair 1B4. A manual feed tray 29 is provided on the right side of the apparatus main body so that it can be turned up and down, and the paper 28 accommodated in the manual feed tray 29 joins the paper feed path from the paper feed cassette 1B1 fed by the paper feed roller 31. The paper is sent toward the registration roller pair 1B4 by the conveying path.

In the optical writing device 5, writing light is controlled by image information from the image reading unit 1C or image information output from a computer (not shown), and the photosensitive drums 3Y, 3M, 3C, and 3B correspond to the image information. Writing light is emitted to form an electrostatic latent image.
The image reading unit 1C includes an automatic document feeder 1C1, a scanner 1C2 having a contact glass 80 as a document table, and the like. The automatic document feeder 1C1 has a configuration capable of reversing the document fed on the contact glass 80, and can perform scanning on each surface of the document.
The electrostatic latent image formed on the photosensitive drum 3 formed by the optical writing device 5 is subjected to visible image processing by the developing device 6 and is primarily transferred to the intermediate transfer belt 2. When the toner images for each color are superimposed and transferred onto the intermediate transfer belt 2, they are secondarily transferred onto the paper 28 by the secondary transfer device 9. The second-transferred paper 28 is sent to the fixing device 11 where the unfixed image is fixed by heat and pressure. Residual toner on the intermediate transfer belt 2 after the secondary transfer is removed by the cleaning device 10.

  The paper 28 that has passed through the fixing device 11 is selectively guided to the conveyance path toward the paper discharge tray 27 and the reverse conveyance path RP by the conveyance path switching claw 12 provided on the downstream side of the fixing apparatus 11. When the paper is conveyed toward the paper discharge tray 27, it is discharged onto the paper discharge tray 27 by the paper discharge roller pair 32 and stacked. When guided to the reversal conveyance path RP, it is reversed by the reversing device 38 and sent again toward the registration roller pair 1B4.

With the above configuration, in the color copying machine 1, the photosensitive drum 3 that is uniformly charged is statically exposed by scanning the document placed on the contact glass 80 or by image information from the computer. An electrostatic latent image is formed, and the electrostatic latent image is subjected to visible image processing by the developing device 6, and then the toner image is primarily transferred to the intermediate transfer belt 2.
In the case of a single image, the toner image transferred to the intermediate transfer belt 2 is transferred as it is to the paper 28 fed out from the paper supply unit 1B. In the case of a multi-color image, the images are superimposed by repeating primary transfer, and then secondary transferred onto the paper 28 at once.
After the secondary transfer, the paper 28 is fixed with an unfixed image by the fixing device 11 and then discharged to the paper discharge tray 27 or reversed and sent again toward the registration roller pair 1B4 for double-sided image formation. In FIG. 16, reference numeral 40 denotes a density detection sensor for detecting the density of the toner pattern.

The configuration of the fixing device 11 will be described in detail below.
As shown in FIG. 1, the fixing device 11 includes an upper unit 50 and a lower unit 52. The upper unit 50 is provided with a fixing roller 54, a heating roller 56, a fixing belt 58 wound around these rollers, a fixing side separation plate unit 60, and the like.
The lower unit 52 includes a pressure roller 62, an entrance guide plate 64 serving as a predetermined position setting member, and a pressure side separation plate unit 66 serving as a separation unit using a predetermined position setting member that separates the paper wound around the pressure roller 62. And a discharge guide means 86 provided on the downstream side of the pressure side separation plate unit 66. The discharge guide means 86 includes a relay discharge guide unit 68 and a discharge guide plate unit 70.
Each of the pressure side separation plate unit 66, the relay paper discharge guide unit 68, and the paper discharge guide plate unit 70 has a length extending in the entire axial direction of the pressure roller 62.

A pressure roller 62 is pressed against the fixing roller 54 via the fixing belt 58 to form a nip portion.
Inside the heating roller 56 and the pressure roller 62, halogen heaters 72 and 74 are incorporated as heat sources, respectively. Although not shown in detail, the halogen heater 72 is composed of a plurality of heaters, and the amount of heating can be controlled by selecting the number of energized wires.
A sheet 28 carrying an unfixed toner image is conveyed from the right side of the figure, and is fixed by being sandwiched and heated at a nip portion.
The fixing belt 58 is formed of a polyimide resin having an inner diameter of 80 mm and a thickness of 90 μm. The surface of the substrate is 200 μm thick silicon rubber, and the outermost layer is coated with a 20 μm thick PFA (tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer) coat. It has the applied structure.
The fixing roller 54 has a heat-resistant / elastic layer made of silicon rubber having an outer diameter of 52 mm and a thickness of 14 mm.
The heating roller 56 is made of an aluminum hollow cylinder having an outer diameter of 40 mm and a thickness of 0.6 mm.
The pressure roller 62 is made of steel and covered with a 1 mm thick hollow core metal covered with 1.5 mm thick silicon rubber. The outermost layer is provided with a PFA (tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer) tube. A roller having an outer diameter of 65 mm.

FIG. 2 shows the appearance of the fixing device 11.
FIG. 3 shows the configuration of the lower unit 52 in a depressurized state in which the pressure roller 62 is separated from the fixing roller 54. The lower unit 52 includes a lower frame unit 73 that is fixed in position, a pressure roller 62, and a pressure roller unit 76 that is provided on the lower frame unit 73 so as to be rotatable in the vertical direction about an axis 75. (Not shown in FIG. 1).
Note that “depressurization” means a concept including both a state in which the pressure roller 62 is completely separated from the fixing belt 58 and a state in which the pressure roller 62 is in contact but not in pressure contact.
The pressure roller unit 76 is driven to rotate by a cam 77 provided in the lower frame unit 73. The cam 77 is fixed to the cam shaft 71, and a rotational force is input from a drive source through a joint (not shown) formed on the cam shaft 71. The cam 77 rotates in the clockwise direction to rotate the pressure roller unit 76 upward to press the pressure roller 62 against the fixing roller 54. When the pressure is released from the pressure contact state, the cam 77 is rotated in the reverse direction.
The pressure roller unit 76 includes an inner lever 78 that is directly driven by a cam 77, and an outer lever 79 that holds both ends of the pressure roller 62 via bearings (not shown). The axis 75 is the center of rotation.
The pressure lever 35 is constituted by the inner lever 78 and the outer lever 79.

The inner lever 75 has a bearing 81 as a rotating roller that contacts the cam surface of the cam 77. The fixing side separation plate unit 60 as a predetermined position setting member is also provided integrally with the pressure roller unit 76.
On the other hand, the discharge guide means 86 is provided in the lower frame unit 73.
The cam 77 has a shape in which the height of the cam surface from the center of rotation gradually increases with the rotation in the direction indicated by the arrow, and the cam 77 rotates to add to the fixing roller 54 via the fixing belt 58. The amount of biting by the pressure roller 62 and its nip width are variable steplessly.
A coil spring 82 as an urging member is set between the inner lever 78 and the outer lever 79, and the pressure direction of the pressure roller 62 (pressure direction) when the pressure roller 62 is in pressure contact with the fixing roller 54. An urging force by the coil spring 82 acts on this. The setting configuration of the coil spring 82 will be described later.

When the cam 77 rotates in the clockwise direction (arrow direction) from the state shown in FIG. 3, the pressure roller unit 76 rotates counterclockwise around the shaft center 75 as shown in FIG. The pressure roller 62 bites into the fixing roller 54 via the fixing belt 58, and a nip portion is formed between the rollers.
FIG. 4 shows a state of pressure 1, which is a pressure state mainly used for fixing thin paper or uncoated paper. In the setting from the depressurized state to the pressure 1 position, the home position is detected by a sensor that detects the position of the cam 77, and the rotation amount from the home position (for example, a predetermined number of steps when the drive source is a stepping motor). This is done under the control of
Further, when the cam 77 rotates in the clockwise direction, as shown in FIG. 5, the amount of biting of the pressure roller 62 toward the fixing roller 54 increases, and a wider nip portion is formed between the rollers. FIG. 5 shows a state of pressure 2, which is a pressure state mainly used for fixing thick paper or coated paper. The setting from the pressure 1 to the pressure 2 is also performed by the same control as described above.

6 is a view showing a state where pressure is released from the state shown in FIG. 4 showing the state of pressure 1 or FIG. 5 showing the state of pressure 2, and the cam 77 is counterclockwise from the state shown in FIG. 4 or FIG. Rotates to a depressurized state.
The cam 77 rotates in the clockwise direction at the time of pressure contact, and rotates counterclockwise at the time of pressure release. That is, the maximum height portion from the center of the cam shaft 71 on the cam surface forms the contact portion with the bearing 81. Since it does not exceed, the direction of the moment applied to the camshaft 71 is applied in the counterclockwise direction during both pressure contact and pressure release, and the direction of the moment applied to the camshaft 71 is not changed by switching from pressure contact to pressure release.
Therefore, when switching from pressure contact to pressure release, there is no gap between the gear meshing portion and between the cam shaft 71 and the joint portion of the drive shaft from a drive source (not shown), thus preventing the generation of abnormal noise. be able to.

FIG. 7 shows the detailed shape of the cam 77. In the cam 77, the contact start portion 7a that starts to contact the bearing 81 from the depressurized state is formed in a smooth curved shape, and on the downstream side of the contact start portion 7a in the pressing direction (arrow P direction) A substantially flat portion 7b is formed. The substantially flat portion 7b is followed by a curved cam surface in which the cam surface height gradually increases.
The angle formed by the line L passing through the center of the cam shaft 71 and the center of the key groove and the horizontal reference point K is the cam position angle θ, and the position of θ = 90 ° is the decompression position (home position).
By rotating in the clockwise direction from the depressurized state, pressurization (pressure contact) proceeds, and from the predetermined pressure contact position, it rotates counterclockwise and returns to the pressure release position.
The rotation range of the cam 77 from the decompression position (home position) is about 0 ° to 315 °, as is apparent from FIG.
In FIG. 7, reference numeral 20 indicates the distance from the cam rotation center to the cam surface, that is, the cam surface height.
FIG. 8A is a graph showing the relationship between the cam surface height 20 and the cam position angle (θ).
As shown in FIG. 8, the cam surface height is a shape that always increases as the cam rotates in the clockwise direction. FIG. 8B shows the relationship between the moment applied to the cam shaft 71 and the cam position angle (θ) with the counterclockwise direction being positive.
From FIG. 8B, the moment acting on the cam shaft 71 is always positive, that is, acts in the counterclockwise direction. If the cam shape at the predetermined pressure contact portion is a shape in which the radius from the cam rotation center is constant, the moment acting on the cam shaft 71 becomes zero, and at this time, the gap between the gear meshing portion and the cam There is a possibility that a gap is generated between the shaft and the joint portion of the drive shaft, and this gap causes noise.
In the present embodiment, the cam shape shown in FIG. 7 always causes a counterclockwise moment to act on the camshaft. Therefore, in a pressurized state, the gap between the gear meshing portion and the joint between the camshaft and the drive shaft No gap is generated between the two, and the generation of abnormal noise can be prevented.

FIG. 9A shows the relationship between the cam surface height change rate (change in cam surface height when the cam angle θ is 1 degree) and the cam position angle (θ) in the cam shape shown in FIG. It is a graph.
In a predetermined pressure contact state such as a pressure 1 state or a pressure 2 state used during paper passing, the cam surface height change rate is 0.05 mm or less per cam rotation angle.
That is, the rate of change of the cam surface height is set to be low at the portion of the cam surface at the use pressure contact position and in the vicinity thereof.
The moment acting on the cam shaft at this time is shown in FIG. From FIG. 9B, the moment acting on the cam shaft is 1.0 N · m or less, and the load on the cam shaft drive motor, the joint portion, and the gear portion can be reduced. Furthermore, even if the value is small, a counterclockwise moment is acting on the camshaft, so that it is possible to prevent the gap between the gear meshing portion and the gap between the camshaft and the drive shaft joint. . 8B and FIG. 9B are the same.

As shown in FIG. 10 (a), a cam position detecting filler 102 is integrally provided at one end of a cam shaft 71 extending in the axial direction of the pressure roller 62. The lower frame unit 73 is provided with a transmissive home position sensor (HP sensor) 103 as cam position detecting means for detecting the cam position detecting filler 102.
A cam upper limit position detecting filler 104 is integrally provided at the other end portion of the cam shaft 71, and a cam upper limit for detecting the cam upper limit position detecting filler 104 is provided in the lower frame unit 73 correspondingly. A transmissive cam upper limit position detection sensor 105 is provided as position detection means.
The cam shaft 71 is driven by a drive source 106 such as a stepping motor or a servo motor provided in the lower frame unit 73.
Here, the home position and the upper limit position of the cam 77 are separately detected, but two positions may be detected by one sensor.

In the depressurized state, the cam position detection filler 102 blocks the HP sensor 103, and a signal indicating the depressurized position is sent to the control means 107 as shown in FIG.
The control means 107 drives the pressure roller 62 in the pressure 1 state shown in FIG. 4 by driving the number of pulses corresponding to the pressure position to be set or the time cam shaft 71 with the home position detected by the HP sensor 103 as a reference. Alternatively, the pressure 2 state shown in FIG. 5 can be arbitrarily set. With this configuration, an arbitrary nip width and nip pressure can be switched according to a difference in mode such as paper type and paper thickness, and an output can be output in an optimum fixing state depending on the paper type and paper thickness.

The rotation of the camshaft 71 in the pressure contact direction continues to increase the amount of biting of the pressure roller 62 with respect to the fixing roller 54. If the camshaft 71 rotates beyond the pressure 2 state shown in FIG. 5, the cam shape shown in FIG. Will suddenly change to a depressurized state, and an abnormal noise as an impact sound will be generated.
In order to prevent this, a cam upper limit position detection sensor 105 is provided for recognizing the position of the cam shaft 71 when the cam shaft 71 rotates beyond the pressure 2 state.
When the cam upper limit position detection filler 104 blocks the cam upper limit position detection sensor 105, a signal indicating the cam upper limit position is sent to the control means 107.
The control means 107 lights or displays an error based on the signal. Alternatively, the control of stopping the rotation of the cam shaft 71 based on the signal and rotating the cam shaft 71 in the reverse direction (depressurization direction) to set the pressure roller 62 to a predetermined pressure position is resumed. Thereby, generation | occurrence | production of the unusual sound which is the said impact sound can be prevented.

In the lower unit 52, the pressure roller unit 76 can be separated from the lower frame unit 73. FIG. 12 is a view of the separated pressure roller unit 76 as viewed obliquely from below.
The configuration of the inner lever 78, the outer lever 79, the bearing 81, the coil spring 82, and the like for rotating the pressure roller unit 76 and the cam 77 are provided on both sides in the axial direction of the pressure roller 62, respectively.
As described above, the pressure roller unit 76 is integrally provided with the entrance guide plate 64 as a predetermined position setting member and the pressure side separation plate unit 66 as a separation means with the predetermined position setting member. The mounting unit 83 is integrally provided.
The pressure electrical unit 83 has a non-contact type thermistor 84 as a predetermined position setting member as a temperature detection means for detecting the surface temperature of the pressure roller 62 and a thermostat 85 as a predetermined position setting member as an excessive temperature rise prevention means. Is provided.

The entrance guide plate 64, the pressure side separation plate unit 66, the thermistor 84, and the thermostat 85 are positioned at predetermined positions with respect to the pressure roller 62 so that these functions can be obtained satisfactorily.
Since these members and the pressure roller 62 are unitized and are displaced together, even if the pressure roller 62 is displaced to a plurality of pressure contact positions according to the paper type, these members and the pressure roller 62 The positional relationship does not change.
Therefore, the conveyance performance by the entrance guide plate 64, the separation performance by the pressure side separation plate unit 66, the temperature detection performance by the thermistor 84, and the excessive temperature rise prevention performance by the thermostat 85 are guaranteed regardless of the displacement of the pressure roller 62.

Next, based on FIG. 13 to FIG. 15, a configuration of a pressure lever responsible for rotation of the pressure roller unit 76 by the cam 77 and a biasing configuration by the coil spring 82 will be described in detail.
As shown in FIG. 13, the outer lever 79 includes an inner lever 91 that holds the pressure roller 62, and an outer lever 93 that is fixed to the inner lever 91 with a bolt 92. The inner lever 91 and the outer lever 93 are formed with insertion holes 94 for inserting the shaft center 75.
A bolt 95 as a support shaft for supporting the coil spring 82 is screwed onto the upper surface of the internal lever 91. The bolt 95 also has a function as a stopper for restricting the upper limit position of the outer lever 79 with respect to the upper unit 50. In FIG. 13, a part of the inner lever 78 is omitted.
FIG. 14 shows the appearance of the inner lever 78. Like the outer lever 79, the inner lever 78 is formed with an insertion hole 96 for inserting the shaft center 75. The inner lever 78 and the outer lever 79 are connected with a predetermined play by a screw shaft 97 that is inserted into a hole 91 a formed in the upper surface of the inner lever 91 and screwed into the inner lever 78.

As shown in FIG. 15, a spring seat 98 of a coil spring 82 is fixed inside the inner lever 78, and a shaft pin 99 that projects horizontally outward is fixed to the spring seat 98. As shown in FIG. 13, the shaft pin 99 is engaged with an elongated hole 100 formed in the external lever 93. With this configuration, the range of deviation between the inner lever 78 and the outer lever 79 due to the displacement of the pressure roller 62 is restricted.
As shown in FIG. 15, the coil spring 82 is set between the spring seat 98 and the upper surface of the internal lever 91. It is the inner lever 78 that is directly driven to rotate by the cam 77. In other words, the cam 77 changes the position of the lower limit (lower end) of the coil spring 82.

When the cam 77 rotates in the clockwise direction as described above, the pressure roller unit 76 rotates upward, and the pressure roller 62 comes into pressure contact with the fixing roller 54 via the fixing belt 58. After the pressure roller 62 is in pressure contact with the fixing roller 54, the coil spring 82 is compressed, and in the state where the pressure roller 62 is in pressure contact, the urging force of the coil spring 82 acts in the pressure contact direction.
When there is no coil spring 82, it becomes pressure contact only by position displacement, and there is no play. By applying the urging force of the coil spring 82, a pressure contact state such as pressure 1 and pressure 2 can be obtained with certainty. In other words, the pressure roller 62 is urged (pressed) by the upper limit (upper end) of the coil spring 82.

In the above-described embodiment, the pressure contact state due to the displacement of the pressure roller 62 includes the pressure 1 state suitable for fixing mainly thin paper and uncoated paper, and the pressure 2 suitable mainly for fixing thick paper and coated paper. However, a large number of pressure contact positions can be obtained by the stepless cam surface shape of the cam 77.
Accordingly, a data table of “paper type and proper press contact position” obtained in advance can be stored in the memory of the control means (not shown), and the optimal press contact position can be selected according to various types of paper. . In this case, the rotation amount of the cam 77 corresponding to the appropriate pressure contact position is controlled by controlling the number of steps of a stepping motor as a drive source of the cam 77, for example.
Further, in the above-described embodiment, the belt fixing type fixing device is illustrated, but the heat roller type fixing device can be similarly implemented.
The present invention can be applied to an apparatus that conveys a sheet material and supplies heat.

35 Pressure Lever 54 Fixing Roller 62 Pressure Roller 71 Cam Shaft 77 Cam 82 Coil Spring as Energizing Member 103 HP Sensor as Cam Position Detection Means 105 Cam Upper Limit Position Detection Sensor as Cam Upper Limit Position Detection Means 106 Drive Source 107 Control means

JP 2008-165091 A JP 2003-15459 A

In order to achieve the above object, according to the first aspect of the present invention, a recording medium holding an unfixed toner image is conveyed to a nip portion between rotating members as fixing members, and is fixed by being sandwiched and heated. In the fixing device, the pressure roller that is one rotating body has a displacement configuration that can be set at a plurality of positions with respect to the fixing roller that is the other rotating body, and both end portions of the pressure roller are respectively In the fixing device including a holding pressure lever and a cam for rotating the pressure lever to displace the pressure roller, the cam is rotated in a certain direction so that the pressure roller is rotated by the fixing roller. The cam surface has a shape that is depressurized by rotation in the reverse direction and the cam surface height constantly increases from the center of the cam shaft according to rotation in the pressure direction. Surface contact position It is a 0.05mm or less per degree change rate of the cam surface height at near, the pressure lever is characterized in that it has a rotary roller in contact with the cam surface of the cam.

According to a second aspect of the present invention, in the fixing device according to the first aspect, the pressing device includes a biasing member that biases the pressure lever in a pressure contact direction with the fixing roller, and the pressure of the biasing member. The position on the side not in contact with the lever is displaced by the rotation of the cam, and the pressure lever is rotated via the urging force of the urging member .
According to a third aspect of the present invention, in the fixing device according to the first or second aspect, a cam position detecting unit that detects the position of the cam, and the cam is driven based on a detection signal from the cam position detecting unit. And a control means for controlling the driving source to displace the position of the pressure roller in accordance with the paper type, paper thickness and mode .
According to a fourth aspect of the present invention, in the fixing device according to any one of the first to third aspects, an upper limit position when the cam rotates in a direction in which the pressure roller is pressed against the fixing roller is detected. Based on the cam upper limit position detecting means and the signal from the cam upper limit position detecting means, an error is lit or the cam is reversely rotated in the pressure-removing direction and the pressure roller is displaced again to a predetermined pressure contact position. It has the control means to control in this way .

According to a fifth aspect of the present invention, in the image forming apparatus , the fixing device according to any one of the first to fourth aspects is provided .

The inner lever 78 has a bearing 81 as a rotating roller that contacts the cam surface of the cam 77. The fixing side separation plate unit 60 as a predetermined position setting member is also provided integrally with the pressure roller unit 76.
On the other hand, the discharge guide means 86 is provided in the lower frame unit 73.
The cam 77 has a shape in which the height of the cam surface from the center of rotation gradually increases with the rotation in the direction indicated by the arrow, and the cam 77 rotates to add to the fixing roller 54 via the fixing belt 58. The amount of biting by the pressure roller 62 and its nip width are variable steplessly.
A coil spring 82 as an urging member is set between the inner lever 78 and the outer lever 79, and the pressure direction of the pressure roller 62 (pressure direction) when the pressure roller 62 is in pressure contact with the fixing roller 54. An urging force by the coil spring 82 acts on this. The setting configuration of the coil spring 82 will be described later.

Claims (7)

A fixing device in which a recording medium holding an unfixed toner image is conveyed to a nip portion between rotating members as fixing members and is fixed by being sandwiched and heated,
The pressure roller that is one rotating body has a displacement structure that can be set at a plurality of positions with respect to the fixing roller that is the other rotating body, and a pressure lever that holds both ends of the pressure roller, A fixing device including a cam for rotating the pressure lever to displace the pressure roller;
The fixing device according to claim 1, wherein the cam has a shape in which the pressure roller is pressed against the fixing roller by rotation in a certain direction and is depressurized by rotation in the reverse direction. The fixing device according to claim 1,
The fixing device according to claim 1, wherein the cam has a shape in which the cam surface height always increases from the center of the cam shaft in accordance with the rotation in the pressing direction. The fixing device according to claim 2,
A fixing device characterized in that, at a predetermined pressure position, a cam surface height change rate in the vicinity of the cam surface contact position is 0.05 mm or less per degree. The fixing device according to any one of claims 1 to 3,
A biasing member that biases the pressure lever in a direction of pressure contact with the fixing roller, and a position of the biasing member that is not in contact with the pressure lever is displaced by rotation of the cam; A fixing device, wherein the pressure lever is rotated via a biasing force of a biasing member. The fixing device according to any one of claims 1 to 4,
Cam position detecting means for detecting the position of the cam, and a driving source for driving the cam based on a detection signal from the cam position detecting means, and the pressure roller according to the paper type, paper thickness and mode. And a control means for displacing the position of the fixing device. In the fixing device according to any one of claims 1 to 5,
A cam upper limit position detecting means for detecting an upper limit position when the cam rotates in a direction in which the pressure roller is pressed against the fixing roller, and an error is lit based on a signal from the cam upper limit position detecting means, or And a control unit that controls the cam to reversely rotate in the pressure-removing direction so that the pressure roller is again displaced to a predetermined pressure contact position.   An image forming apparatus comprising the fixing device according to claim 1.

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