JP6149441B2 - Fixing apparatus and image forming apparatus - Google Patents

Description

  The present invention relates to a fixing device used in an electrophotographic image forming apparatus such as a copying machine, a facsimile machine, and a printer. More specifically, a nip portion is formed between an endless fixing member and a pressure member. The present invention relates to a fixing device that performs a fixing process on a recording medium passing through the nip portion, and an image forming apparatus equipped with the fixing device.

In recent years, market demands such as energy saving and high speed are increasing for image forming apparatuses such as printers, copiers, and facsimiles.
The image forming apparatus uses an image forming process such as electrophotographic recording, electrostatic recording, magnetic recording, etc., an image transfer method or a direct method to transfer an unfixed toner image to a recording material sheet, printing paper, photosensitive paper, electrostatic recording paper, etc. Formed on a recording medium. As a fixing device for fixing an unfixed toner image, a fixing device using a contact heating method such as a heat roller method, a film heating method, and an electromagnetic induction heating method is widely used.
As an example of such a fixing device, a belt type fixing device (for example, Patent Document 1) and a surf fixing (film fixing) type fixing device using a ceramic heater (for example, Patent Document 2) are known. .

In belt-type fixing devices, in recent years, further warm-up time (time required from normal temperature state such as when the power is turned on to the reload temperature at which printing can be performed) and first print time (after receiving a print request and undergoing print preparation) It is desired to shorten the time required for completing the paper discharge after the printing operation (Problem 1).
In addition, as the speed of image forming apparatuses increases, the number of sheets passed per unit time increases and the required heat quantity increases, so the problem of a lack of heat quantity at the beginning of continuous printing, so-called temperature drop, becomes a problem. A solution is desired (Problem 2).
As a method for solving the problem 1, surf fixing using a ceramic heater has been proposed. According to this surf fixing method, it is possible to reduce the heat capacity and reduce the size as compared with the belt-type fixing device. However, since only the nip portion is locally heated, the other portions are not heated, and the belt is in the coldest state at the paper inlet of the nip portion, so that there is a problem that fixing failure is likely to occur.
Further, in the belt-type high-speed machine, there is a problem that fixing failure is more likely to occur because the rotation of the endless belt is fast and the heat dissipation of the endless belt is increased at a portion other than the nip (problem 3).
In order to solve the above problems 1 to 3, in the configuration using an endless belt, the entire endless belt can be warmed, the first print time from the heating standby time can be shortened, and at the time of high-speed rotation A fixing device has been proposed in which a sufficient fixing property can be obtained even if it is mounted on a high-production image forming apparatus by eliminating the shortage of heat quantity (Patent Document 3).

FIG. 11 is a schematic diagram of a fixing device 200 described in Patent Document 3. The pipe-shaped metal heat conductor 202 fixed inside the fixing belt 201 is disposed so as to guide the movement of the fixing belt 201 in the rotation direction. The heat source 203 in the metal heat conductor 202 heats the metal heat. The fixing belt 201 is heated via the conductor 202. Furthermore, a pressure roller 204 that forms the nip portion N by contacting the metal heat conductor 202 via the fixing belt 201 is provided, and the fixing belt 201 is rotated in the circumferential direction so as to rotate with the rotation of the pressure roller 204. Move. With this configuration, it is possible to warm the entire fixing belt constituting the fixing device, shorten the first print time from the standby time of heating, and solve the shortage of heat during high-speed rotation. Yes.
A transfer roller 220 and a registration roller pair 221 are disposed on the upstream side of the fixing device 200 in the transport direction.
In order to further save energy and improve the first print time, a configuration has been proposed in which the fixing belt is heated indirectly via a metal heat conductor, and the fixing belt is directly heated without the metal heat conductor. Yes. With this configuration, it is possible to reduce the power consumption by greatly improving the heat transfer efficiency and to further shorten the first print time from the heating standby time. Further, the cost can be reduced by eliminating the metal heat conductor.

By the way, when the recording medium is jammed in the fixing device 200, control for jam processing is performed to reversely rotate the pressure roller and reverse the fixing belt.
There are two reasons why the pressure roller 204 and the fixing belt 201 are reversely rotated when a jam occurs.
The first reason is to improve the removability of the recording medium sandwiched in the nip between the pressure roller and the fixing belt. By rotating the pressure roller and the fixing belt in the reverse direction, the recording medium that has entered the back of the nip can be pulled out to the inlet side of the nip, and it is easy to grasp the extracted recording medium by hand. Because it becomes.
The second reason is to prevent the occurrence of plastic deformation (hereinafter referred to as kink) due to thermal deformation of the fixing belt 201 as a fixing member. The glass tube of the heater that constitutes the heat source 203 inside the fixing belt becomes very hot during heat generation. When the rotation of the pressure roller and the fixing belt is stopped due to the clogging of the recording medium, even if the power supply to the heat source is stopped, the heat source and the nearest fixing belt part are locally localized due to the residual heat on the surface of the heater glass tube. Increase in temperature. As a result, thermal deformation occurs in a portion heated to a high temperature due to a temperature difference from the fixing belt portion separated from the heat source, and a kink state is obtained as it is. In addition, when the recording medium is jammed, the leading edge of the recording medium may be close to the high-temperature portion. In this case, the leading edge of the recording medium may be discolored, burned, or smoked.
In such a case, if the fixing belt is reversely rotated by a certain amount, it is possible to save time and wait for the remaining heat of the heater glass tube to be radiated.

However, if the fixing belt 201 is reversely rotated when a recording medium jam occurs, the following problems occur. 12A to 12D are schematic diagrams showing a jam processing procedure in a fixing device of a fixing belt type that does not use a metal heat conductor.
12A shows a normal fixing state, FIG. 12B shows a state in which the pressure roller and the fixing belt are stopped due to occurrence of a recording medium jam, and FIG. 12C shows a pressure roller for jam processing. And (d) shows a state in which the recording medium is wound around the fixing belt by the reverse rotation.
In the state of FIG. 12A, the pressure roller 204 and the fixing belt 201 are rotated in the normal fixing direction. However, when it is detected that the recording medium P has jammed as shown in FIG. The control means that does not stops the motor that drives the pressure roller to stop both rollers. Next, the control means reverses both rollers as shown in (c) to return the recording medium P clogged in the nip portion N to the inlet side of the nip portion, thereby facilitating taking out the recording medium by manual work. Further, when the fixing belt 201 is reversed, it is possible to prevent the fixing belt from being kinked due to the heat from the heat source 203 being applied to the local portion of the fixing belt.

Separating means 210 is a means for separating the recording medium to be wound around the fixing belt when the fixing belt is rotated in reverse by causing the tip to protrude toward the inlet side of the nip portion N.
The dimension of the gap S between the separating unit 210 and the fixing belt 201 is set to be constant assuming a recording medium (for example, plain paper) having a standard thickness.
However, if the recording medium is thin paper or a lot of unfixed toner adheres to the recording surface as in a photographic image, the recording medium sticks to the fixing belt 201 during the reverse operation shown in (d). In this state, the separation means 210 passes through the tip and is rotated in reverse. Then, the recording medium reaches the high temperature portion H of the fixing belt, and discoloration, scorching, smoke generation, etc. occur.
The probability that such a problem occurs is not uniform due to the difference in the type of recording medium such as paper thickness, size, and material, and the state of the recording medium such as the toner image area.

In Patent Document 4, a reverse rotation switch for operating when a paper jam occurs is provided. When this switch is pressed, the fixing roller reversely rotates to facilitate removal of the paper.
However, depending on conditions such as the thickness, size, material, and toner image area of the recording medium (ease of winding around the fixing belt at the time of reverse rotation), prevention of winding at the time of reverse rotation, discoloration due to winding, scoring, fuming No proposal has been made to prevent it properly.
In particular, in a fixing device using a fixing belt having a structure in which only both ends in the axial direction are held by a holding member without using a metal heat conductor as a fixing member, there is no means for supporting most of the fixing belt. The fixing belt that has fallen in strength is easily deformed. For this reason, it is difficult to peel off the recording medium adsorbed on the surface of the fixing belt only by simply rotating the fixing belt in the reverse direction.
However, by changing the pattern of reverse rotation operation according to the difference in the type and state of the recording medium such as paper thickness, size, material, image area, etc., the recording medium can be prevented from being caught during reverse rotation and the efficiency of separation can be improved. No proposal has been made.

As described above, as a method for improving the energy efficiency and the first print time and further improving the thermal efficiency, an endless fixing member, that is, a fixing belt, is indirectly connected through a metal heat conductor disposed on the inner side. From the configuration in which the fixing belt is heated, a configuration in which the fixing belt is directly heated without using a metal heat conductor has been proposed. However, since the fixing belt not supported by the metal heat conductor is easily deformed, the recording medium adsorbed on the surface of the fixing belt via the toner image can be easily peeled off simply by reversing the fixing belt for jamming. A phenomenon that does not happen. In addition, no consideration has been given to the difference in these conditions so far, even though the conditions for eliminating the entrainment of the recording medium differ depending on the thickness, size, material, and toner image area of the recording medium. It was.
The present invention has been made in view of the above, and in a fixing device that uses an endless fixing belt with a low heat capacity as a fixing member and directly heats the fixing belt with an internal heat source. Therefore, when the fixing belt is rotated in the reverse direction, the separation failure such as the winding of the recording medium depends on the conditions such as the thickness, size and image area of the recording medium (difference in the ease of winding of the recording medium by the fixing belt). An object of the present invention is to propose a fixing device that can be effectively solved.

In order to achieve the above object, a fixing device according to the present invention includes a heat source, an endless fixing member that is rotatably supported by the heat source, and is in contact with the fixing member. A pressure roller that forms a nip portion, a drive source that rotates the fixing member forward and backward, a separating unit that prevents the fixing member from winding the recording medium when the fixing member rotates reversely, and a drive source Control means for controlling the fixing device, wherein the control means changes the operation pattern during reverse rotation according to the type and state of the recording medium, and the fixing member. Control for changing the amount of rotation at the time of reverse rotation is performed .

  According to the present invention, an endless fixing belt having a low heat capacity is used as a fixing member, and the fixing belt is directly heated by an internal heat source, according to the type and state of the recording medium. Thus, control is performed to change the reverse rotation pattern of the fixing belt during jam processing. For this reason, the separation failure such as the winding of the recording medium when the fixing belt is rotated reversely for the jam processing, the conditions such as the thickness, size, and image area of the recording medium (ease of winding of the recording medium by the fixing belt). The difference can be effectively resolved according to the difference.

1 is a diagram illustrating a configuration of an example of an image forming apparatus including a fixing device of the present invention. 1 is a configuration diagram illustrating a fixing device according to an embodiment of the present invention. (A) thru | or (d) is explanatory drawing which showed the behavior of the fixing belt at the time of reverse rotation in relation to the separation means 154. 4 is a flowchart illustrating a procedure for reversely rotating a fixing belt in the embodiment. It is a block diagram of a fixing device of a type using a plurality of different lengths of halon heaters used as a heat source. It is an expanded view of a light shielding member. (A) And (b) is the figure which showed the concealment state (light-shielding state) of the heat source by the light-shielding member at the time of A3 size paper passing and postcard size paper passing. FIG. 10 is a diagram showing an experimental result in which whether or not a recording medium that has clogged is caught for each size of the recording medium when jamming is eliminated by reverse rotation of the fixing belt is checked. 10 is a flowchart illustrating a procedure for reversely rotating a fixing belt in a fifth embodiment. 14 is a flowchart illustrating a procedure for reversely rotating a fixing belt in a sixth embodiment. 10 is a schematic diagram of a fixing device described in Patent Document 3. FIG. (A) thru | or (d) is the schematic which shows the jam processing procedure in the fixing device of a fixing belt type of a type which does not use a metal heat conductor.

Hereinafter, the present invention will be described in detail with reference to embodiments shown in the drawings.
FIG. 1 is a diagram for explaining the configuration of an example of an image forming apparatus provided with the fixing device of the present invention.
The image forming apparatus 1 is a color printer that uses a tandem method in which image forming units that form a plurality of color images are juxtaposed along the belt extending direction. However, the present invention is not limited to this method, and only the printer is used. It is also possible to target a copying machine or a facsimile machine instead.
The image forming apparatus 1 includes photosensitive drums 20Y, 20C, 20M, and 20Bk as image carriers that can form images as images corresponding to colors separated into yellow, cyan, magenta, and black, respectively. The installed tandem structure is adopted.

A toner image formed on each of the photoconductive drums 20Y, 20C, 20M, and 20Bk is an intermediate transfer body (hereinafter referred to as a transfer belt) 11 that is an endless belt that moves in the direction of arrow A1 while facing the photoconductive drums. Then, the toner images are primarily transferred and the toner images are superimposed and transferred. Thereafter, batch transfer (primary transfer) is performed on a recording medium P such as recording paper.
Around each photosensitive drum, an apparatus for image forming processing is arranged according to the rotation of the photosensitive drum. To describe the photosensitive drum 20Bk that performs black image formation, a charging device 30Bk, a developing device 40Bk, a primary transfer roller 12Bk, and a cleaning device 50Bk that perform image forming processing along the rotation direction of the photosensitive drum 20Bk are arranged. ing. The optical writing device 8 is used for writing (electrostatic latent image formation) performed after charging.

The transfer belt 11 is supported by a driving roller 72 and a driven roller 73.
In the superimposed transfer of each color toner image onto the transfer belt 11, the toner images formed on the photosensitive drums 20 </ b> Y, 20 </ b> C, 20 </ b> M, and 20 </ b> Bk are placed at the same position on the transfer belt 11 in the process of moving the transfer belt 11 in the A1 direction. The voltage is applied by the primary transfer rollers 12Y, 12C, 12M, and 12Bk so that the images are transferred in a superimposed manner with the timing shifted from the upstream side toward the downstream side in the A1 direction.
The photosensitive drums 20Y, 20C, 20M, and 20Bk are arranged in this order from the upstream side in the A1 direction.
Above each of the photoconductive drums 20Y, 20C, 20M, and 20Bk, a transfer belt unit 10 that includes the transfer belt 11 and the primary transfer rollers 12Y, 12C, 12M, and 12Bk is disposed so as to face each other. Further, a secondary transfer roller 5 that is driven by the transfer belt 11 and an intermediate transfer belt cleaning device 13 that is disposed to face the transfer belt 11 and cleans the transfer belt 11 are disposed.

Further, the sheet feeding device 61 as a sheet feeding cassette loaded with a recording medium conveyed toward the secondary transfer portion between each photosensitive drum and the transfer belt 11, and the sheet feeding device 61 has conveyed the sheet feeding device 61. The registration roller pair 4 that feeds the recording medium toward the secondary transfer portion between each photosensitive drum and the transfer belt 11 at a predetermined timing in accordance with the toner image formation timing, and the leading end of the recording medium is a resist. A sensor (not shown) for detecting that the roller pair 4 has been reached is provided.
Further, the image forming apparatus 1 includes a fixing device 100 as a belt-fixing type fixing unit for fixing the toner image to the recording medium P to which the toner image is transferred, and a fixed recording medium of the image forming apparatus 1. A paper discharge roller 7 that discharges to the outside of the main body, a paper discharge tray 17 that is disposed in the upper part of the main body of the image forming apparatus 1 and loads a recording medium discharged by the paper discharge roller 7, and a lower side of the paper discharge tray 17. And toner bottles 9Y, 9C, 9M and 9Bk which are filled with toners of respective colors of yellow, cyan, magenta and black.
The sheet feeding device 61 has a feeding roller 3 as a paper feeding roller that abuts on the upper surface of the uppermost recording medium. When the feeding roller 3 is rotationally driven in the counterclockwise direction, The upper recording medium is fed toward the registration roller pair 4.

FIG. 2 is a configuration diagram showing a fixing device according to an embodiment of the present invention.
The fixing device 100 includes a fixing belt 101 as an endless (annular) fixing member inside the casing, a heat source 105 including a halogen heater, and a pressure roller 150 as a pressure member. As a result, the fixing belt 101 is directly heated from the inner peripheral side.
Inside the endless fixing belt 101, there is a nip forming member 120 that forms a nip portion N with a pressure roller 150 opposed via the fixing belt 101, and directly on the inner surface of the fixing belt (or a sliding sheet (not shown)). To slide indirectly).
In FIG. 2, the nip portion N has a flat shape, but may have a concave shape or other shapes. When the nip portion is concave, the discharge direction at the front end of the recording medium is closer to the pressure roller, and the separation is improved, so that jamming is suppressed.

The fixing belt 101 is an endless belt (or film) using a thin metal plate such as nickel or SUS or a thin plate made of a resin material such as polyimide as a base material. A release layer such as a PFA layer or a PTFE layer is formed on the surface layer of the fixing belt so as to prevent the toner from adhering. There may be an elastic layer formed of a silicone rubber layer or the like between the base material of the fixing belt and the release layer. When there is no silicone rubber layer, the heat capacity is reduced and the fixability is improved, but when the unfixed image is crushed and fixed, minute irregularities on the belt surface are transferred to the image, and the image has a crusty skin shape. There arises a problem that the gloss unevenness (zudder skin image) remains. In order to improve this, it is necessary to provide a silicone rubber layer of 100 [μm] or more. Due to the deformation of the silicone rubber layer, fine irregularities are absorbed and the skin image is improved.
A support member 122 (stay) for supporting the nip forming member 120 is provided inside the fixing belt 101 to prevent the nip forming member 120 that receives pressure from the pressure roller 150 from being bent and to have a uniform nip width in the axial direction. So that you can get The support member 122 is positioned and held at both ends in the axial direction by holding members 125 (flange) that rotatably hold the both ends of the fixing belt. In addition, a reflection member 127 is provided between the heat source 105 and the support member 122, and wasteful energy consumption due to the support member 122 being heated by radiation heat from the heat source 105 or the like is suppressed. Here, instead of providing the reflecting member 127, the same effect can be obtained even if the surface of the supporting member 122 is heat-insulated or mirror-finished.
A belt protection member 129 is disposed in the outer diameter direction of the fixing belt 101, and abuts against the belt protection member 129 when the fixing belt is deformed in the outer diameter direction by driving from the pressure roller 150. The protection member 129 may be rotated along with the rotation of the fixing belt, or may be configured to remain stationary.

The heat source 105 may be the illustrated halogen heater, but may be IH (Induction Heating), a resistance heating element, a carbon heater, or the like.
The pressure roller 150 is provided with an elastic rubber layer 152 on the peripheral surface of the core metal 151, and a release layer (PFA or PTFE layer) is provided on the surface in order to obtain releasability. The pressure roller 150 is rotated by a driving force transmitted from a driving source 155 such as a motor provided in the image forming apparatus via a gear. The pressure roller 150 is pressed against the fixing belt 101 by a spring or the like, and has a predetermined nip width when the elastic rubber layer 152 is crushed and deformed. The pressure roller 150 may be a hollow roller, and the pressure roller 150 may have a heat source such as a halogen heater. The elastic rubber layer 152 may be solid rubber, but if there is no heater inside the pressure roller 150, sponge rubber may be used. Sponge rubber is more desirable because it increases heat insulation and makes it difficult for the fixing belt to lose heat.

The fixing belt 101 rotates when the driving force from the pressure roller 150 rotated by the driving source 155 is transmitted to the fixing belt at the nip portion N. The fixing belt 101 rotates while being sandwiched between the pressure roller and the support member 122 at the nip portion N, and the inner periphery of both end openings is held by the holding member 125 (flange) other than the nip portion (both axial end portions). And is guided to rotate freely.
With the above configuration, it is possible to realize a fixing device that is inexpensive and has a fast warm-up.

<Characteristic configuration of the present invention>
3A to 3D are explanatory views showing the behavior of the fixing belt during reverse rotation in relation to the separating unit 154. FIG.
A fixing device 100 according to the first embodiment of the present invention includes a heat source 105, an endless fixing belt (fixing member) 101 that has a heat source therein and is rotatably supported and heated by the heat source. A pressure roller (pressure member) 150 that forms the nip portion N in contact with the outer peripheral surface of the fixing belt, a drive source 155 that rotates the fixing belt 101 forward and backward, and a recording medium is positioned in the nip portion N. A separation unit 154 that prevents the recording medium from being caught when the fixing belt rotates in the reverse direction, and a control unit 160 that controls the drive source 155. Furthermore, the control unit 160 changes the operation pattern during reverse rotation according to the type of the recording medium (thickness, size, material) and the state of the recording medium (unfixed toner image area).

Depending on the type and state of the recording medium, the ease of winding (ease of sticking) when the fixing belt is reversed during jamming differs.
The type and state of the recording medium are recognized by the control means in advance by key input from the operation panel of the image forming apparatus main body, or detected by a sensor provided in the image forming apparatus, and this is notified to the control means. For example, information on the thickness, size, and material of the recording medium can be input by key input, and the thickness and size can be detected by a sensor. Further, the area of the toner image can be determined from the recording medium size, the image area in the read image, the scaling factor, and the like.

  In this embodiment, the operation pattern at the time of reverse rotation is changed according to the type (thickness, size, material) and state (toner image area) of the recording medium P, so that it is wound around the outer periphery of the fixing belt at the time of reverse rotation. The recording medium P (to be attracted) can be forcibly separated (separated) by the separating means 154. That is, when the jammed recording medium is jammed by the reverse rotation of the fixing belt in the fixing device, depending on the type and state (thickness, size, material, and toner image area of the recording medium) By changing the reverse rotation pattern (reverse rotation amount, reverse rotation speed, etc.), it is possible to make the recording medium after reverse transport easier to separate. For this reason, the recording medium is wound around the outer periphery of the fixing belt during the reverse rotation, and discoloration, scorching, smoke generation, etc. caused by continuing contact with the high temperature portion of the fixing belt can be prevented, and the recording medium removal workability is improved.

Next, in the fixing device 100 according to the second embodiment of the present invention, the rotation speed when the control unit 160 reversely rotates the fixing belt 101 by the drive source 155 is the type (thickness, size, It is characteristic that various changes are made depending on the material) and the state of the recording medium (toner image area).
That is, the operation pattern of the fixing belt controlled by the control unit is the speed at the time of reverse rotation in this example.
At the time of reverse rotation of the fixing belt 101, the relationship between tension and slackness of the fixing belt is reversed from that at the time of forward rotation. As shown in FIG. 3A, during the forward rotation of the fixing belt, the inlet side of the nip portion N is in a stretched state (the state farthest from the separating means 154, S = maximum), and the outlet side of the nip portion N is loosened. However, at the time of reverse rotation, the inlet side of the nip portion becomes a slack side (a state approaching the separating means 154, S = minimum). Therefore, the higher the reverse rotation speed of the fixing belt, the narrower the gap S between the fixing belt 101 and the separating unit 154 during the reverse rotation. In this embodiment, when a recording medium having a property of being easily wound during reverse rotation is jammed, the clearance S is narrowed by increasing the reverse rotation speed to narrow the gap S, so that the separation is performed by the tip of the separation unit 154 disposed in the vicinity of the nip entrance. (Fig. 3 (c)). Thereby, it is possible to prevent the recording medium from being caught between the fixing belt and the separating unit and reach a portion heated to a high temperature by a heat source, and to prevent discoloration, scorching, and smoke generation of the recording medium (FIG. 3D). .

  For example, the separating means 154 is composed of a sheet metal member or a resin member, and is installed on the bottom frame of the fixing device (not shown) or by setting a part of the cover covering the fixing device in such a shape. To do. At the time of reverse rotation of the fixing belt, the leading end portion of the separating means 154 is relatively expanded between the fixing belt that has expanded toward the separating means and the recording medium to be wound around the outer surface of the fixing belt. By inserting the recording medium, the recording medium can be separated from the fixing belt (FIG. 3D).

The gap S between the fixing belt and the separating unit is set assuming a recording medium with a normal thickness, and is not suitable for separating thin paper when the fixing belt is reversed (the gap is too wide). is there.
In the present embodiment, the rotation speed when the fixing belt is reversely rotated by the drive source is set based on the ease with which the recording medium P is wound around the fixing belt. Conditions relating to the ease of winding are the thickness of the recording medium and the area of the recorded toner image.
If the recording medium is thin paper or highly flexible (low elasticity), it is easy to wrap around the outer surface of the fixing belt that reverses, and if it is thick paper, it is strong (elastic) unlike thin paper. Hard to stick and difficult to get caught during reverse rotation. Therefore, for example, when the jammed recording medium is thin paper, the clearance S between the separation unit 154 is increased by increasing the speed at the time of reverse rotation and increasing the amount of looseness of the fixing belt on the entrance side of the nip portion N. To make it easy to separate by the separating means. In the case of thick paper that is difficult to be caught during reverse rotation, there is no problem even if the reverse rotation speed is slower than that of thin paper (plain paper). Information on whether the recording medium being used is easy to wrap around the fixing belt, in other words, whether it is thin paper, is input in advance by key input from the operation panel of the image forming apparatus, or by a paper passing sensor. It can be obtained by detecting the translucency of the recording medium.

  Also, if a recording medium carrying an image with a large amount of unfixed toner, such as a photograph or a picture, is clogged in the fixing device, if the reverse rotation is performed, it is easy to wind around the fixing belt due to the increased adhesion of toner. Become. Also in this case, as in the case of thin paper, the fixing belt is slackened toward the separating unit 154 by increasing the speed at the time of reverse rotation, and the gap with the separating unit is narrowed to make it easy to separate. Conversely, when a recording medium carrying an unfixed toner image with a small amount of toner, such as a character image, is clogged in the fixing device, the adhesion of the toner is weak, so that it is difficult to stick to the fixing belt and the recording medium is caught. Since reverse rotation is difficult, reverse rotation may be slow. In the present invention, the reverse rotation speed is 77 mm / s when winding is easy such as thin paper and plain paper, and 56 mm / s for other paper types. Information about the amount of unfixed toner on the recording medium can be obtained from image information when an image is formed in the image forming unit of the main body of the image forming apparatus.

FIG. 4 is a flowchart showing a procedure for reversely rotating the fixing belt in the embodiment.
When the image forming apparatus 1 starts the image forming operation and the fixing device 100 starts the fixing operation and a jam occurs in the fixing device (S1 to 3, S4 YES), the drive source 155 is stopped (S5). ). If it is determined in step 6 that the jammed recording medium is thin paper, in step 7, the drive source is rotated faster than the normal reverse rotation speed. When the door is opened and jam processing is performed to clear the jam and the door is closed, the image forming operation is resumed (S8 to 11).
If it is determined in step 6 that the paper is not thin but thick in step 12, the drive source is reversely rotated at the normal speed or slower than the normal speed (S13).
Next, in the fixing device 100 according to the third embodiment of the present invention, the reverse rotation amount when the control unit 160 reversely rotates the fixing belt 101 by the drive source 155 is the type (thickness, size) of the recording medium P. , Material) and the state of the recording medium (toner image area).

That is, the operation pattern of the fixing belt controlled by the control unit is the reverse rotation amount (rotation angle) at the time of reverse rotation in this example.
The controller 160 controls the heat generation temperature by the heat source to be lower than when fixing plain paper or thick paper when fixing thin paper that requires a small amount of fixing heat. The temperature detector 166 detects the temperature of the heat source or the fixing belt.

The reverse rotation operation of the fixing belt performed when the recording medium is jammed in the fixing device is intended to prevent kinking due to partial overheating of the fixing belt. In general, thin paper has a low fixing set temperature, and thick paper has a high set temperature. The fixing heat amount (heat source set temperature) when fixing thin paper is set lower than the fixing heat amount when fixing thick paper. For this reason, since the kink by the residual heat of the heater glass tube surface which comprises the heat source 105 does not occur easily, reverse rotation amount can be reduced. For this reason, the control means controls to reduce the reverse rotation amount (reverse rotation direction movement amount) when the thin paper is passed. By reducing the amount of reverse rotation when clogging occurs during the passage of thin paper, the amount of thin paper rolled up can be reduced.
In the case of thin paper, the recording medium is easily caught between the separating means and the fixing belt. For this reason, if the amount of reverse rotation is large, when the recording medium is caught between the separating means and the fixing belt, the amount of the recording medium also increases, so it is difficult to remove the recording medium. For this reason, in the case of thin paper, by reducing the reverse rotation amount, it is possible to improve the jam handling performance while suppressing discoloration, scorching and smoke generation of the recording medium.

Even when the image area of the recording medium is large, entanglement is likely to occur, which makes it easier to reduce jamming by reducing the reverse rotation amount of the fixing belt.
In the present invention, the reverse rotation amount (the amount of movement of the fixing belt) is set to, for example, 50 mm when thin paper is used, and the reverse rotation amount is set to 75 mm for other paper types.

  The reverse rotation control procedure of the fixing belt according to the third embodiment will be described based on the flow of FIG. 4. In the case of thin paper in step 6, the reverse rotation amount is decreased in step 7 than in the normal case. Further, in the case of thick paper in step 12, the reverse rotation amount is made normal in step 13 or is made smaller than normal.

Next, in the fixing device 100 according to the fourth embodiment of the present invention, the reverse rotation speed or / and the reverse rotation amount (rotation angle) when the control unit 160 reversely rotates the fixing belt 101 by the drive source 155. ) Is variously changed according to the difference in thickness (thickness) of the recording medium P.
Specifically, when the recording medium P that is clogged in the fixing device is thin paper (thin recording medium) that tends to be wound, control is performed to increase the reverse rotation speed and reduce the reverse rotation amount. On the other hand, when the paper is thick paper (thick recording medium), the reverse rotation speed is controlled to be slow, and the rotation amount is controlled to be larger than that of the thin paper.
Note that only control for increasing the reverse rotation speed may be performed when the paper is thin (thin recording medium), and only control for decreasing the reverse rotation speed may be performed when the paper is thick (thick recording medium). That is, in the present embodiment, the reverse rotation speed may be controlled only according to the thickness of the recording medium, and the reverse rotation amount may not be controlled, or only the reverse rotation amount may be controlled. .

Depending on the thickness of the recording medium, the degree of ease of sticking to the fixing belt by reverse rotation when clogging occurs in the fixing device varies. Since the thick paper is difficult to stick to the fixing belt at the time of reverse rotation and the gap S with the separating means can be widened, the reverse rotation speed of the fixing belt is slowed. On the contrary, the thin paper increases the reverse rotation speed because the separation means comes into contact with the recording medium and cannot be separated if the gap S with the separation means is wide. By increasing the reverse rotation speed of the fixing belt, the fixing belt portion on the entrance side of the nip portion N is expanded toward the separating means, and the gap S with the separating means is narrowed. For this reason, a separation means can be inserted between the recording medium that rotates in reverse with the fixing belt and the fixing belt (FIGS. 3C and 3D).
Further, in the present embodiment, when the recording medium causing the jam in the fixing device is thin paper, the reverse rotation speed of the fixing belt is increased and the reverse rotation amount (reverse rotation direction movement amount) is reduced. When the thick paper is jammed, the reverse rotation speed of the fixing belt is slow and the rotation amount is increased. Thus, the reverse rotation conditions (reverse rotation speed and reverse rotation amount) are changed depending on whether the recording medium is thin or thick.

  The reverse rotation control procedure of the fixing belt according to the fourth embodiment will be described with reference to the flow of FIG. 4. In the case of thin paper in Step 6, the reverse rotation speed of the fixing belt is increased in Step 7 and the reverse rotation amount is set. It will be less than usual. In the case of thick paper in step 12, the reverse rotation measure is made normal or slow in step 13, and the reverse rotation amount is made normal or larger than normal.

Next, in the fixing device 100 according to the fifth embodiment of the present invention, the reverse rotation speed and the reverse rotation amount when the control unit 160 reversely rotates the fixing belt 101 by the drive source 155 are set to the recording medium P. It is characteristic that various changes are made according to the difference in size (length in the transport direction).
Specifically, the recording medium that has become jammed in the fixing device is nipped by the secondary transfer roller 5 or the registration roller 4 disposed on the conveyance path to the fixing device at the time of the jamming. Depending on whether or not there is, the occurrence rate of winding around the reversely rotating fixing belt varies.

Whether or not the rear portion of the recording medium is sandwiched between the secondary transfer roller 5 and the registration roller 4 when the fixing device stops driving due to the occurrence of a paper jam due to the difference in the size of the recording medium (length in the conveyance direction). Is decided.
Even if the recording media have the same size, the length in the transport direction differs if the transport direction is different. Therefore, the size of the recording medium referred to here is the size in the transport direction.

In FIG. 5, in order to adjust the light emission area from the heat source 105 in accordance with the difference in the width direction size of the recording paper, a plurality of halon heaters having different lengths (two in this example) are used as the heat source. It is a block diagram of a type fixing device.
Since the light emission range in the axial direction of each halogen heater is different, the fixing belt can be optimally heated for various sizes of recording media.
In the embodiment of FIG. 5, the light emission range of the heat source is further adjusted by the light shielding member 110 interposed between the heat source 105 and the inner peripheral surface of the fixing belt 101. The light shielding member 110 is a plate material having a light shielding property curved in an arc shape.

  FIG. 6 is a development view of the light shielding member 110, and the light shielding member 110 has a stepped shape for varying the light shielding area according to the width dimension of the recording medium P to be passed. In this example, a portion 110a having an opening width corresponding to the postcard size, a portion 110b having an opening width facing the B4 size, and a portion 110c having an opening width facing the A3 size are provided.

FIGS. 7A and 7B are views showing the concealed state (light-shielded state) of the heat source by the light-shielding member when A3 size paper is passed and postcard size paper is passed.
The light shielding member 110 is disposed so as to rotate in a non-contact manner along the inner side of the fixing belt 101, and rotates a portion corresponding to a position corresponding to a difference in the width dimension of each recording medium to prevent heating. Necessary areas are shielded from light (FIG. 7).
As a result, even when a narrow recording medium is continuously fed, the non-sheet passing area is not overheated, and control such as reducing productivity to cancel the overheated area is performed. There is no need to do it. In addition, with the use of the light shielding member, the number of halogen heaters can be reduced from three to two.

Next, FIG. 8 is a result of an experiment in which the presence / absence of winding (recovery allowance) in the case where the jamming is eliminated by reverse rotation of the fixing belt for each size of the recording medium. Is shown. Depending on whether the recording medium remains in the nip portion of the registration roller 4 located farther from the fixing device or in the nip portion of the secondary transfer roller 5 near the fixing device, the ease with which the recording medium can be wound varies. . As a result of the experiment, when the recording medium is not nipped by the registration roller 4 but is nipped by the secondary transfer roller 5 and there is a slack between the secondary transfer roller and the fixing device, entanglement occurs. .
As described above, when the recording medium that is likely to be caught is passed according to the difference in conditions such as the recording medium size and the paper passing direction, the reverse rotation speed for eliminating the jam is increased. The clearance between the separation unit 154 and the fixing belt is increased by increasing the reverse rotation speed of the fixing belt so that the jammed recording medium approaches the separation unit 154 and is easily separated from the fixing belt by contact with the separation unit. By narrowing S, separation can be promoted and the recording medium can be prevented from being caught in the fixing belt.

FIG. 9 is a flowchart showing a procedure for reversely rotating the fixing belt in the embodiment.
When the image forming apparatus 1 starts the image forming operation and the fixing device 100 starts the fixing operation and a jam occurs in the fixing device (S21 to 23, S24 YES), the drive source 155 is stopped (S25). ). If it is determined in step 26 that the conveyance direction size of the recording medium causing the jam is longer than the reference value, the drive source is rotated faster than the normal reverse rotation speed in step 27. When the door is opened and jam processing is performed to clear the jam and the door is closed, the image forming operation is resumed (S28-31).
If it is determined in step 26 that the conveyance direction size of the recording medium is shorter than the reference value, the drive source is reversely rotated at the normal speed or slower than the normal speed (S32).
Here, the reference value means that the recording medium is not nipped by the registration roller 4 as shown in FIG. 8, but is nipped by the secondary transfer roller 5, and the relationship between the secondary transfer roller and the fixing device. This is the length of the recording medium in the conveyance direction when there is a slack between them.

Next, in the fixing device 100 according to the sixth embodiment of the present invention, the control unit 160 determines the reverse rotation speed when the control belt 160 rotates the fixing belt in the reverse direction by the drive source and is carried on the recording surface of the recording medium P. It is characteristic that various changes are made according to the area (amount) of the toner.
Specifically, when the image area (unfixed toner amount) on the recording medium that is clogged in the fixing device is large enough to cause wrapping (for example, a photographic image), the reverse rotation speed is increased. On the other hand, when the image area is small enough to prevent winding (for example, a character image), the reverse rotation speed is controlled to be slow.

Even if the recording medium has the same thickness, if the image area made of the unfixed toner carried is wider than a preset reference value, the recording medium tends to stick to the fixing belt, and as a result, the separating means The recording medium is easily caught between the toner and the fixing belt, and the recording medium is likely to be discolored or smoked by heat from the heat source. Accordingly, when the image area is larger than the predetermined reference value, the clearance S between the fixing belt and the separating unit 154 is secured by increasing the reverse rotation speed so as to ensure a large slack of the fixing belt on the entrance side of the nip portion N. Narrow and prevent the recording medium from being caught.
The control unit 160 determines whether the image is a toner-rich image from the print image information from the PC or the like and the print image information from the scanner.
In addition, when the toner image area is smaller than the reference value or when the toner image area is smaller than the reference value, the toner image area may be divided into a plurality of stages, and the reverse rotation measure may be sequentially increased according to each stage.

FIG. 10 is a flowchart showing a procedure for reversely rotating the fixing belt in the embodiment.
When the image forming apparatus 1 starts the image forming operation and the fixing device 100 starts the fixing operation and a jam occurs in the fixing device (S41 to 43, S44 YES), the drive source 155 is stopped (S45). ). If it is determined in step 46 that the image area on the recording surface of the recording medium causing the jam is larger than the reference value, the drive source is rotated faster than the normal reverse speed in step 27. When the door is opened and jam processing is performed to clear the jam and the door is closed, the image forming operation is resumed (S48-51).
If it is determined in step 46 that the image area of the recording medium is smaller than the reference value, the drive source is reversely rotated at the normal speed or slower than the normal speed (S52).
Here, the reference value is a reference for determining whether the image area is wide enough to cause the recording medium to be caught.

<Summary of Configuration, Action, and Effect of the Present Invention>
The fixing device 100 according to the first aspect of the present invention includes a heat source 105, an endless fixing member (fixing belt) 101 having the heat source therein and rotatably supported by the heat source, and fixing. A pressure roller 150 that forms a nip portion in contact with the outer peripheral surface of the belt, a driving source 155 that rotates the fixing belt forward and backward by rotating the pressure member forward and backward, and a drive source 155 that rotates backward. A separation unit 154 that prevents the fixing belt from entraining the recording medium, and a control unit 160 that controls the drive source are provided. The control unit changes the operation pattern during reverse rotation according to the type and state of the recording medium. Control.
By configuring and controlling in this way, it is possible to prevent the recording medium from being caught between the fixing belt and the separating unit (the outer peripheral surface of the fixing belt) during reverse rotation of the fixing belt. It is possible to make it easy to separate. In particular, change the reverse rotation pattern (reverse rotation amount, rotation speed) according to the state of the recording medium (paper thickness, image area size, transport direction size) that is about to jam. Thus, the reversely transported recording medium can be more easily separated. For this reason, the recording medium is wound between the fixing belt and the separating means during the reverse rotation, and it is possible to prevent smoke generation, paper discoloration, and the like caused by contact with the high temperature portion of the fixing belt, and paper removability is improved.

In the fixing device 100 according to the second aspect of the present invention, the control means performs control to change the rotation speed of the fixing belt 101 during reverse rotation.
When the fixing belt 101 rotates in the reverse direction, the relationship between the tension and the slackness of the fixing belt is reversed from that in the normal rotation, and the entrance side of the nip portion becomes the slack side. Accordingly, the faster the reverse rotation speed, the narrower the gap S between the rotating fixing constant belt and the separating means. In the case of a recording medium that is easily wound during reverse rotation, the reverse rotation speed is increased so that the recording medium can be easily separated by the separating means disposed in the vicinity of the nip entrance. Thereby, it is possible to prevent the recording medium from being caught between the fixing belt and the separating unit, and it is possible to prevent the recording medium from being burnt or discolored.

In the fixing device 100 according to the third aspect of the present invention, the control means performs control to change the rotation amount of the fixing belt 101 during reverse rotation.
When a thin paper (thin recording medium) is passed through the fixing device, the fixing temperature of the heat source is set low, so that kinks due to thermal deformation of the fixing belt do not occur even if the reverse rotation amount is small. In the case of thin paper, since the recording medium is easily caught between the separating unit and the fixing belt, if the reverse rotation amount is large, the amount of the rolled-in paper increases when the recording medium is caught between the separating unit and the fixing belt. Therefore, it is difficult to remove the paper. For this reason, in the case of thin paper, by reducing the reverse rotation amount, it is possible to improve the jam handling performance while suppressing the burning and discoloration of the recording medium.

In the fixing device 100 according to the fourth aspect of the present invention, the control means performs control to change the rotation speed and / or the reverse rotation amount of the fixing belt during the reverse rotation according to the difference in the thickness of the recording medium. .
Depending on the thickness of the recording medium, the degree of sticking to the fixing belt due to reverse rotation when a paper jam occurs varies. In the case of thick paper, it does not stick to the fixing belt at the time of reverse rotation (= there is no problem even if the gap with the separating means is wide), so the rotation speed at the time of reverse rotation is slowed down. On the other hand, in the case of thin paper, the recording medium cannot be separated if the gap with the separation means is wide.Therefore, the reverse rotation speed is increased and the gap between the separation means is narrowed by bulging the inlet side of the nip portion. The reversely rotated recording medium can be separated by the separating means.

In the fixing device 100 according to the fifth aspect of the present invention, the control means performs control to change the rotational speed at the time of reverse rotation of the fixing belt according to the difference in the length of the recording medium in the conveyance direction.
Depending on the direction and size of the recording medium, when a jam occurs in the fixing device, the rear portion of the recording medium may be sandwiched between the secondary transfer unit and the registration roller pair. As described above, the wrap-around margin at the time of reverse rotation of the fixing belt varies depending on whether or not the recording medium is sandwiched between the pair of rollers arranged in the conveyance path on the distillation side of the fixing device. In the case of a size that can be easily wound, the rotational speed during reverse rotation is increased, and the gap S between the fixing belt and the separating unit is narrowed so that the recording medium is not caught.

In the fixing device 100 according to the sixth aspect of the present invention, the control means performs control to change the rotation speed at the time of reverse rotation of the fixing belt according to the difference in the image area (unfixed toner amount) on the recording medium.
Even if the thickness of the recording medium is the same, if the image area is large, the recording medium is likely to stick to the fixing belt, and as a result, the recording medium is likely to be caught between the separating means and the fixing belt. Easy to lead to discoloration and smoke. Therefore, when the image area is large, the reverse rotation speed is increased to narrow the gap between the fixing belt and the separating unit so that the recording medium is not caught.

DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus, 3 ... Feeding roller, 4 ... Registration roller pair, 5 ... Secondary transfer roller, 7 ... Paper discharge roller, 8 ... Optical writing device, 9 ... Toner bottle, 10 ... Transfer belt unit, 11 DESCRIPTION OF SYMBOLS ... Transfer belt, 13 ... Intermediate transfer belt cleaning device, 17 ... Paper discharge tray, 20 ... Photosensitive drum, 30 ... Charging device, 40 ... Developing device, 50 ... Cleaning device, 61 ... Sheet feeding device, 72 ... Drive roller 73 ... driven roller, 100 ... fixing device, 101 ... fixing belt (fixing member), 105 ... heat source, 110 ... light shielding member, 120 ... nip forming member, 122 ... support member, 125 ... holding member, 127 ... reflecting member, 129: Belt protective member, 150: Pressure roller, 151: Metal core, 152: Elastic rubber layer, 154: Separating means, 155: Driving source (motor), 160: Control means, 166 Temperature detecting means, 221 ... pair of registration rollers.

JP 2004-286922 A Japanese Patent No. 2861280 JP 2007-334205 A Japanese Patent Laid-Open No. 06-191102

Claims (2)

A heat source, an endless fixing member that is rotatably supported by the heat source and heated by the heat source, a pressure roller that forms a nip portion in contact with the fixing member, and the fixing member A fixing device comprising: a driving source for rotating the recording medium forward and backward; a separating unit for preventing the fixing member from entraining the recording medium when rotated reversely; and a control unit for controlling the driving source. And
The control means performs control for changing an operation pattern at the time of reverse rotation and control for changing an amount of rotation at the time of reverse rotation of the fixing member according to a difference in type and state of the recording medium. A fixing device characterized. An image forming apparatus comprising the fixing device according to claim 1 .

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