JP5091558B2 - Fixing apparatus and image forming apparatus - Google Patents

Description

  The present invention relates to a copying machine having a fixing device that heats and fixes unfixed paper between a rotatable fixing roller having a plurality of heating sources therein and a pressure roller that presses and presses against the fixing roller. In particular, the present invention relates to an image forming apparatus such as a laser printer, and more particularly to a fixing apparatus that can reliably achieve separation of a sheet from a fixing roller.

In general, an image forming apparatus such as a copying machine or a laser printer includes a rotatable fixing roller having a plurality of heating sources therein and a pressure roller that presses and presses the fixing roller. A fixing device that heats and fixes an unfixed sheet between the pressure rollers is used.
As a conventional technique, a temperature and a cooling method when a fixing belt is used and a belt and a sheet are peeled are proposed (Patent Documents 1 and 2). Here, the cooling effect is recognized because each cooling means is provided, but because of the use of a special cooling means and the increased number of parts due to the use of the belt fixing system, each in terms of cost. The point which becomes expensive and the point which requires space are mentioned as a subject.

As another conventional technique, a technique using a fixing roller and also having a cooling means has been proposed (Patent Document 3).
Although the effect of the cooling means is recognized here as well, since the paper from the nip to the cooling separation is directly subjected to the heat of the heater at the portion where it contacts the roller, the cooling effect at that portion cannot be obtained, and depending on the timing of the heater lighting On the other hand, there is a problem that heating may occur, and cost increases due to the use of special cooling means.
JP 2005-181474 A Japanese Patent Laid-Open No. 5-273766 JP 2001-235958 A

The above-described prior art aims to improve image quality by sufficiently cooling the sheet when it is separated from the fixing member after being heated at the fixing nip. Another effect of cooling is separation of the paper from the fixing member.
In general, in black-and-white image forming apparatuses, a sheet such as a claw with a sharp tip is brought into contact with the downstream side of the fixing nip to separate sheets. However, under various conditions, separation becomes insufficient and sheet jam occurs. It sometimes occurred.
In addition, the color image forming apparatus has stricter requirements for image quality than the black and white image forming apparatus, and the fixing member which has been mainly used in the black and white image forming apparatus is brought into contact with a member such as a claw having a sharp tip to forcibly separate it. Such a method causes deterioration in image quality such as unevenness of image gloss, for example, because the surface property of the fixing member is different from other portions in the portion that directly contacts the fixing member.

Therefore, in the color image forming apparatus, for example, a non-contact type separation method such as a plate-like member (separation plate) over the entire sheet passing width adjacent to the fixing member with a minute gap is used. It cannot be denied that the separation performance is reduced as compared with the contact type. A factor contributing to the separation performance is the fixing member temperature when the paper and the fixing member are separated. As described in Patent Document 2, the tendency of “cohesive force between toners”> “adhesive force between toner and fixing member” becomes stronger and the separation performance is improved when cooled. Although the cooling means is disclosed in the prior art, there are problems in terms of cost and space because of the belt fixing device and the use of special cooling means.
SUMMARY An advantage of some aspects of the invention is that it provides a fixing device that can reliably achieve separation of a sheet from a fixing roller in an image forming apparatus. .

To achieve the above object, a first aspect of the present invention, which incorporates a heat source, a rotatable fixing roller for heating the interior by heat source, fixing roller and the pressure to pressurize the pressure roller DOO has, the fixing roller and the nip formed by the heating roller to a fixing device for heating and pressurizing pressure fixing a sheet of unfixed, inside the fixing roller, and a pre-Symbol heat source the nip And a shielding member that shields radiant heat radiated from the heat source toward the nip portion, the shielding member being movable in the circumferential direction within the fixing roller, and with respect to the nip portion The fixing device is characterized in that the region heated by the radiant heat in the nip portion can be changed by changing the position .
According to a second aspect of the present invention, the temperature of the fixing roller necessary for fixing an unfixed image is T1, and the separation resistance when the sheet is separated from the fixing roller after passing through the nip portion is predetermined. the temperature of the fixing roller becomes a value less than when the T2, the temperature Tin of the fixing roller of the nip portion immediately before is formed by the pressure roller and the fixing roller is controlled to be above T1, the Temperature control means for controlling the temperature of the fixing roller immediately after the nip portion by controlling the position of the shielding member so that the temperature Tout of the fixing roller is equal to or lower than T2 and T1> T2.

According to a third aspect of the present invention, the shielding member includes an auxiliary shielding member superimposed on the shielding member, and the shielding range of the shielding member is changed when the auxiliary shielding member moves in the fixing roller. The fixing device according to claim 1, wherein the fixing device can be used.
According to a fourth aspect of the present invention, there is provided the fixing device according to the third aspect, wherein the position and the shielding range of the shielding member are selected according to a plurality of sheet conveyance speeds.
According to a fifth aspect of the invention, there is provided the fixing device according to the third aspect, wherein a position and a shielding range of the shielding member are selected according to an installation environment of the fixing device.
According to a sixth aspect of the present invention, there is provided the fixing device according to the third aspect, wherein a position and a shielding range of the shielding member are changed in accordance with the number of passing sheets .
According to a seventh aspect of the present invention, the fixing member according to the third aspect is configured such that the position and the shielding range of the shielding member are selected differently during warm-up operation, standby, and paper passing of the fixing device. Features the device .

According to an eighth aspect of the invention, there is provided the fixing device according to any one of the first to seventh aspects , wherein a non-contact separating unit is used as the sheet separating unit from the fixing roller.
According to a ninth aspect of the present invention, there is provided an image forming apparatus having the fixing device according to any one of the first to eighth aspects .

According to the present invention, there is a shielding member that is disposed inside the fixing roller and that can selectively heat the inside of the fixing roller, the fixing roller temperature necessary for fixing is T1, and the sheet is fixed after passing through the nip portion. When the fixing roller temperature at which the separating force when peeling from the roller becomes a predetermined value or less is T2, the fixing roller temperature immediately before the nip formed by the fixing roller and the pressure roller is T1 or more and the fixing roller temperature immediately after the nip Is T2 or less and T1> T2 is controlled, so that separation of the sheet from the fixing roller can be reliably achieved with an inexpensive configuration.
Further, according to the present invention, the shielding member shields the vicinity of the nip formed by the fixing roller and the pressure roller and avoids direct heating of the nip portion from the heating source, so that the sheet is separated from the fixing roller. This can be achieved with an inexpensive configuration.

Further, according to the present invention, since the shielding member is configured to be movable in the fixing roller, the sheet separation temperature of the fixing roller corresponding to the optimum separation condition depending on the printing conditions can be controlled with an inexpensive structure. Separation of the paper from the fuser roller can be achieved.
According to the present invention, since the shielding member is configured to be able to change the shielding range, the fixing roller can be controlled by controlling the sheet separation temperature of the fixing roller corresponding to the optimum separation condition depending on the printing conditions with an inexpensive configuration. Separation of the paper from the can be achieved.
Further, according to the present invention, since the shielding member position and range are selected according to a plurality of paper conveyance speeds, the temperature at the time of paper separation of the fixing roller corresponding to the optimum separation condition depending on the paper conveyance speed is controlled with an inexpensive configuration. Thus, separation of the sheet from the fixing roller can be achieved.

Further, according to the present invention, since the position and range of the shielding member are selected according to the installation environment of the apparatus, the fixing roller can be controlled by controlling the temperature at the time of paper separation of the fixing roller corresponding to the optimum separation condition depending on the installation environment with an inexpensive configuration. Separation of the paper from the can be achieved.
Further, according to the present invention, since the position and range of the shielding member are changed according to the number of sheets to be passed, it is possible to control the temperature at the time of sheet separation of the fixing roller corresponding to optimum separation conditions depending on the number of sheets to be passed with an inexpensive configuration. Thus, separation of the sheet from the fixing roller can be achieved.
Further, according to the present invention, since different shielding member positions and ranges are selected for the warm-up operation, standby, and paper passing, the required items such as paper separation and warm-up time are shortened, and the temperature drop immediately after the start of paper feeding is specified. It can be established.
Further, according to the present invention, since the shielding member is installed between the plurality of heating sources, separation of the sheet from the fixing roller can be achieved with an inexpensive configuration.

Further, according to the present invention, since different shielding member positions and ranges are selected at the time of warm-up operation and paper passing, required items such as paper separation, shortening of warm-up time, prevention of temperature drop immediately after the start of paper passing can be satisfied. Can do.
Further, according to the present invention, since at least one of the plurality of heating sources is forcibly turned off depending on the size of paper to be passed, the temperature at the time of paper separation of the fixing roller corresponding to the optimum separation condition depending on the paper size can be reduced. In this way, separation of the sheet from the fixing roller can be achieved.
Further, according to the present invention, the separation of the sheet from the fixing roller can be achieved with an inexpensive configuration even in the non-contact separation unit.
In addition, according to the present invention, since the fixing device that can reliably achieve the separation of the sheet from the fixing roller is provided, the sheet separation in the image forming apparatus can be reliably achieved.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
Here, an embodiment in which the present invention is applied to a color laser printer (hereinafter simply referred to as “printer”) as an image forming apparatus will be described.
FIG. 1 is a schematic block diagram of an embodiment of a printer according to the present invention.
As shown in FIG. 1, this printer is configured such that four image forming units of yellow, cyan, magenta, and black are arranged side by side to form a tandem image forming unit. In the tandem image forming unit, The image forming units 101Y, 101C, 101M, and 101K as individual toner image forming units are sequentially arranged from the left in the figure. Here, the suffixes Y, C, M, and K of the respective symbols indicate members for yellow, magenta, cyan, and black, respectively.
In the tandem image forming unit, the individual image forming units 101Y, 101C, 101M, and 101K are arranged around the drum-shaped photosensitive members 21Y, 21C, 21M, and 21K as latent image carriers, and the charging device and the developing device 10Y. 10C, 10M, 10K, photoconductor cleaning device and the like.

In addition, toner bottles 2Y, 2C, 2M, and 2K filled with yellow, cyan, magenta, and black color toners are disposed at the top of the printer. Then, each color toner is supplied from the toner bottles 2Y, 2C, 2M, and 2K to the respective color developing devices 10Y, 10C, 10M, and 10K by a predetermined supply amount through a conveyance path (not shown).
Further, an optical writing unit 9 as a latent image forming unit is provided below the tandem image forming unit. The optical writing unit 9 includes a light source, a polygon mirror, an f-θ lens, a reflection mirror, and the like, and irradiates the surface of each of the photoreceptors 21Y, 21C, 21M, and 21K while scanning the laser beam based on the image data. It is configured as follows.
Further, an endless belt-like intermediate transfer belt 1 is provided as an intermediate transfer body immediately above the tandem image forming unit. The intermediate transfer belt 1 is wound around support rollers 1a and 1b, and a drive motor (not shown) serving as a drive source is connected to a rotation shaft of the drive roller 1a among the support rollers. When this drive motor is driven, the intermediate transfer belt 1 rotates counterclockwise in the figure and the followable support roller 1b rotates. Inside the intermediate transfer belt 1, primary transfer devices 11Y, 11C, 11M, and 11K for transferring the toner images formed on the photoreceptors 21Y, 21C, 21M, and 21K onto the intermediate transfer belt 1 are provided. Yes.

Further, a secondary transfer roller 4 as a secondary transfer device is provided downstream of the primary transfer devices 11Y, 11C, 11M, and 11K in the driving direction of the intermediate transfer belt 1. A support roller 1b is disposed on the opposite side of the secondary transfer roller 4 and the intermediate transfer belt 1 and functions as a pressing member.
Further, a paper feed cassette 8, a paper feed roller 7, a registration roller 6, and the like are provided, and the downstream side of the secondary transfer roller 4 with respect to the traveling direction of the recording medium (transfer paper) S on which the toner image is transferred by the secondary transfer roller 4. The unit includes a fixing device 5 for fixing an image on the recording medium S and a paper discharge roller 3.

Next, an image forming operation of the printer will be described.
First, the photoconductors 21Y, 21C, 21M, and 21K are rotated. Along with the rotation of the photoconductors 21Y, 21C, 21M, and 21K, first, the charging devices 17Y, 17C, 17M, and 17K use the photoconductors 21Y, 21C, 21M, and 21K. The surface is uniformly charged. Next, image data is irradiated with writing light by a laser from the optical writing unit 9 to form electrostatic latent images on the photoreceptors 21Y, 21C, 21M, and 21K. Thereafter, toner is attached by the developing devices 10Y, 10C, 10M, and 10K, and the electrostatic latent images are visualized to form yellow, cyan, magenta, and black on the photoreceptors 21Y, 21C, 21M, and 21K, respectively. A monochromatic image is formed.
Further, the driving roller 1a is rotationally driven by a driving motor (not shown), the other driven roller 1b and the secondary transfer roller 4 are driven to rotate, the intermediate transfer belt 1 is rotated and conveyed, and the visible image is transferred to the primary transfer device. The images are sequentially transferred onto the intermediate transfer belt 1 by 11Y, 11C, 11M, and 11K. As a result, a composite color image is formed on the intermediate transfer belt 1. The surface of the photoconductors 21Y, 21C, 21M, and 21K after image transfer is cleaned by removing residual toner with a photoconductor cleaning device to prepare for image formation again.

In accordance with the timing of image formation, the leading edge of the recording medium S is fed from the paper feed cassette 8 by the paper feed roller 7 and conveyed to the registration roller 6 and temporarily stops. Then, the sheet is conveyed between the secondary transfer roller 4 and the intermediate transfer belt 1 while taking timing with the image forming operation. Here, the intermediate transfer belt 1 and the secondary transfer counter roller 5 form a so-called secondary transfer nip with the recording medium S interposed therebetween, and the secondary transfer roller 4 transfers the toner image on the intermediate transfer belt 1 to the recording medium S. Secondary transfer on top.
The recording medium S after the image transfer is sent to the fixing device 5, and as shown in FIG. 8, a fixing roller 51 having a heating source 53 therein and maintaining the surface at a predetermined temperature by the temperature control means, and fixing. The sheet is nipped and conveyed to a nip formed by a pressure roller 52 facing the roller 51 and pressed against the fixing roller 51, whereby the toner image on the sheet is heated and pressed to be fixed on the sheet.
Further, the paper discharged from the nip portion is separated by the separating member and then discharged from the paper discharge roller 3 to the outside of the apparatus. On the other hand, the intermediate transfer belt 1 after the image transfer is removed by the intermediate transfer body cleaning device 12 to remove residual toner remaining on the intermediate transfer belt 1 after the image transfer, so that the tandem image forming unit prepares for another image formation.

Next, the fixing device 5 which is a main part of the present invention will be described.
First, in order to fix the toner image on the paper, a predetermined fixing temperature at the fixing nip, a predetermined pressure, and a predetermined heating and pressing time are required. This predetermined condition mainly depends on the characteristics of the toner, but is determined by the amount of toner adhered per unit area, the installation environment of the device, the type of paper, etc., but has a specific range depending on the fixing device. It becomes.
Here, T1 is the optimum fixing temperature for fixing the toner image determined from the above various conditions on the paper. The optimum temperature is a value having a range, but here, the significance of indicating the lower limit in the optimum range is large. Next, separation of the paper discharged from the fixing nip from the fixing roller 51 will be considered. As stated for the purpose of the invention, it is advantageous for the fixing temperature to be lower for paper separation. The condition for separating the sheet from the fixing roller is also a value having a specific range depending on the fixing device, but the upper limit temperature at which separation from the fixing roller 51 can be achieved is T2. That is, this T2 is the temperature of the fixing roller 51 at which the separation resistance when peeling from the fixing roller 51 becomes a predetermined value or less.

  Next, as an index for determining whether or not separation can be achieved, the peeling force between the sheet that has passed through the fixing nip and the fixing roller 51 is considered. A sheet with a uniform toner adhesion amount is passed through the fixing device. Here, as shown in FIG. 2, immediately after the fixing nip, as a separation resistance measuring device for measuring the separation resistance, a detection claw 41 for measurement is provided on the fixing roller 51 side. Since the sheet that has passed through the fixing nip is conveyed with a force that winds around the fixing roller 51, the sheet is conveyed while being pressed against the detection claw 41. The pressing force at this time is read by the load cell 42 provided at the other end of the detection claw 41. This value is a force required to peel the sheet from the fixing roller 51, and this is a separation resistance force. It is determined whether or not the sheet can be separated from the fixing roller 51 based on the magnitude of the separation resistance measured under the predetermined condition.

FIG. 2 is a schematic configuration diagram of the separation resistance measuring device in the printer shown in FIG. FIG. 3 is a graph showing a change in the separation resistance between the fixing roller 51 and the sheet with respect to the fixing temperature. FIG. 3 is a graph in which the fixing temperature is plotted on the horizontal axis and the separation resistance between the fixing roller 51 and the paper is plotted on the vertical axis.
As shown in FIG. 3, each value varies depending on external conditions such as the conditions unique to the apparatus and the installation environment, but the tendency is the same, with the peak around the optimum fixing temperature, and the separation resistance as the distance increases. Will decrease.

In the case of this example, the separation resistance decreases as the fixing temperature decreases with the peak at the separation resistance of 160 ° C. to 170 ° C. In this fixing device, it has been found that separation of the sheet from the fixing roller 51 can be achieved if the separation resistance is 30 gf or less. The level at which separation can be achieved here means that when the detection claw 41 is used as a separation member, the sheet can be passed without jamming even when the toner image is printed up to the leading edge of the sheet. When a non-contact separating plate is used as the separating member, it means that the sheet can be passed without jamming in a state where the leading edge margin of the sheet is 2 mm and printed.
On the other hand, the optimum fixing temperature is 160 ° C. to 180 ° C. in an example fixing device, and the relationship between T1 and T2 is shown in FIG. The curve in the figure represents the relationship between the separation resistance force and the fixing temperature shown in FIG. The fixing temperature indicated by the intersection of this curve and the horizontal broken line is T2 described above. On the other hand, the optimum fixing temperature T1 is indicated by a vertical broken line. FIG. 4 is a graph showing the relationship between the separation resistance and the fixing temperature.

As described above, the separation resistance in the vicinity of the optimum fixing temperature shown in FIG. 4 often takes a peak value, and a range in which the optimum fixing region and the separable region are compatible cannot be obtained. The separation resistance is reduced by half when it falls by 10 deg to 20 deg from the optimum fixing temperature, and at this time, it is often a separable region.
Here, as shown in FIG. 5, the fixing temperature T is divided into a nip inlet temperature (temperature of the fixing roller 51 immediately before the nip portion) Tin and a nip outlet temperature (temperature of the fixing roller 51 immediately after the nip portion) Tout. FIG. 5 is an explanatory diagram showing the concept of the nip inlet temperature Tin and the nip outlet temperature Tout.
As shown in FIG. 5, the amount of heat necessary to ensure the fixing property is the temperature of the entire region from Tin to Tout, but the temperature is controlled before the nip inlet, and the nip inlet temperature Tin is a representative value. Is considered. On the other hand, the temperature affecting the separation is the toner temperature immediately after the nip, and the fixing roller temperature immediately after the fixing nip is discharged, that is, the nip outlet temperature Tout can be considered as a representative value. In general, both the optimum fixing temperature T1 and the separable temperature T2 are considered with the nip inlet temperature Tin. This is because the nip outlet temperature Tout is considered to be a temperature obtained by uniformly reducing the amount of heat taken by the nip from the nip inlet temperature Tin. In the present invention, the nip inlet temperature Tin and the separable temperature T2 are set for the optimum fixing temperature T1. Is considered at the nip outlet temperature Tout. As described above, before and after the nip, the sheet and the pressure roller 52 are deprived of heat, so that the nip inlet temperature Tin> the nip outlet temperature Tout.

FIG. 6 is a graph showing changes in the nip inlet temperature Tin and the nip outlet temperature Tout with respect to time. As shown in FIG. 6, the normal fixing temperature is controlled by the temperature controller 54 (see FIG. 5) so that the fixing inlet temperature Tin becomes the optimal fixing temperature T1 (or higher).
Although the nip outlet temperature Tout is not particularly controlled, heat is taken away at the nip as described above, so that the temperature transition obtained by subtracting the amount of heat taken away from the temperature of Tin as shown by the broken curve in the figure is changed from the nip inlet to the nip outlet. Appears delayed by the rotation time until (delay indicated by block arrow). It is general from the relationship between the nip inlet temperature Tin and the nip outlet temperature Tout due to the heat deprived in the nip described above and the value obtained by subtracting a fixed temperature from the fixable temperature T1 as the separable temperature T2. In such a fixing device, it can be seen that the nip outlet temperature Tout is equal to or lower than the separable temperature T2.

However, it can be said that the fixing temperature control is usually performed while detecting the temperature near the nip inlet temperature, and the nip inlet temperature Tin is controlled. For this reason, the nip outlet temperature Tout may become Tout> T2 depending on the lighting timing of the heating source 53. In this case, the heating source 53 is turned on when the control unit temperature Ts (Tin) decreases. At this time, since the fixing roller 51 is heated not only at the temperature detecting portion but also around the entire circumference, the nip outlet temperature Tout is uniformly heated regardless of the temperature at that time, and the nip outlet temperature Tout increases. If the nip outlet temperature Tout at this time shows a value near the nip possible temperature T2, for example, it results in deviating from the separable range as indicated by Tout 'in the figure.
Thus, in order to prevent the downstream area, mainly the nip portion from being heated more than necessary and exceeding the separable temperature T2 from the temperature detecting portion on the fixing roller 51, the heat amount of the heating source 53 is changed to the nip portion. Think not to give directly.
Therefore, in this embodiment, as shown in FIG. 7, a shielding plate 55a is provided between the inside of the nip portion in the fixing roller 51 and the heating source 53, thereby preventing direct heating of the nip portion. As a result, the fixing roller temperature behavior that has exceeded the separable temperature T2 shown in Tout ′ of FIG. 6 becomes the temperature behavior indicated by the broken line T obtained by subtracting the amount of heat absorbed by the nip from the nip inlet temperature Tin, and the nip outlet temperature Tout. Is controlled below the separable temperature T2.

Here, FIG. 8 shows a perspective view of the shielding plate 55a. The shielding plate 55a is disposed substantially in parallel with the heating source 53 inside the fixing roller 51, and regulates the amount of heat transmitted to the nip portion over the entire sheet passing width. As for the method of attaching the shielding plate 55a, both ends thereof are fixed to part of the housing with a stepped screw or the like in consideration of thermal expansion absorption. FIG. 8 is a perspective view of a shielding plate 55 a provided between the inside of the nip portion in the fixing roller 51 and the heating source 53.
As described above, according to the present exemplary embodiment, the shielding member that is disposed inside the fixing roller and that can selectively heat the inside of the fixing roller is provided. When the fixing roller temperature at which the separation force when peeling from the fixing roller after passing through the portion becomes a predetermined value or less is T2, the fixing roller temperature immediately before the nip formed by the fixing roller and the pressure roller is T1 or more, Since the fixing roller temperature immediately after the section is T2 or less and T1> T2, the separation of the sheet from the fixing roller can be reliably achieved with an inexpensive configuration.

Next, consider a case where conditions such as the thickness of the fixing roller 51 and the rotation speed of the fixing roller 51 are different. The shielding range by the shielding plate 55 and the appropriate range of the shielding position, in which the fixing temperature T1 for securing the fixing property and the fixing temperature T2 for securing the separation property are compatible, differ depending on the conditions. The heat transfer time from the inner peripheral surface of the fixing roller 51 that receives heat from the heat source 53 determined by the thickness and material of the fixing roller 51 to the outer peripheral surface that directly contacts the toner and gives the heat, and fixing during the transfer time It is necessary to determine the shielding position and shielding range in consideration of the distance that the roller 51 moves by rotation.
For example, as the thickness of the fixing roller 51 increases, the heat transfer time becomes longer. Therefore, the amount of heat received by the fixing roller 51 further upstream is transferred to the toner at the nip portion. That is, the thicker the wall thickness, the more it is necessary to shield the upstream side of the nip portion, and it is necessary to widen the shielding range. However, when the wall thickness is increased and the heat storage amount of the fixing roller 51 is increased, the amount of heat lost by the nip can be sufficiently compensated by the heat storage amount of the fixing roller 51, so that the temperature drop amount of the nip outlet temperature To decreases. is necessary. Similarly, as the rotation speed of the fixing roller 51 increases, the amount of heat received by the fixing roller 51 further upstream is transmitted to the toner at the nip portion. As the rotational speed increases, it is necessary to shield the upstream side of the nip portion, and it is necessary to arrange the shielding range on the upstream side.

Here, in order to increase the pixel density, a case where the linear speed is variable such as halving the linear speed (paper conveyance speed) at the time of high-quality printing is considered. In this case, the shielding range or position where the separable temperature is optimally obtained varies depending on the linear velocity for the reasons described above. In such a case, it is conceivable that the range or position of the shielding plate 55a is made variable and is changed to an optimum range or position depending on the linear speed (paper conveyance speed).
For the reasons described above, it is considered effective to set the shielding plate 55a so as to directly shield the nip portion as shown in FIG. FIG. 7 is a schematic view when the shielding plate 55a is provided at a position where the nip portion is directly shielded.
Further, at the time of high-speed printing, it is considered effective to set the position of the shielding plate 55a as shown in FIG. 9 moved to the upstream side. FIG. 9 is a schematic configuration diagram when the shielding plate 55a is provided at a position moved upstream.

Similarly, consider a case where the shielding range is changed. As an example of a means for changing the shielding range, consider that a shielding plate as shown in FIG. 10 has a double structure. Similarly, at the time of low-speed printing for the reasons described above, it is considered that the separable temperature is optimal by setting the shielding range in which two shielding plates 55a and 55b are overlapped as shown in FIG. In high-speed printing, it is considered that the separable temperature is optimal by moving the shielding plate 55b to widen the shielding range as shown in FIG. The temperature control means is constituted by the shielding plate 55 and the position changing means of the shielding plate 55. The temperature control means is specifically composed of a microcomputer or the like that controls various parts including the position change of the shielding plate 55 according to each detection result.
FIG. 10 is a schematic configuration diagram of a state in which the shielding range is narrow by overlapping two shielding plates 55a and 55b. FIG. 11 is a schematic configuration diagram in a state where the shielding plate 55b is moved and the shielding range is wide.

Here, a perspective view of a specific example of variable shielding plate position for realizing the embodiment shown in FIGS. 7 and 9 is shown in FIG. FIG. 12 is a perspective view of a specific example of variable shielding plate position.
As shown in FIG. 12, the shielding plate 55 is held by holding members 56 that can swing at both ends. The holding member 56 can rotate around the rotation fulcrum and can move the movable range of the shielding plate 55 as shown in FIGS. The movement is generally performed by a combination of a solenoid 57 and an elastic member 58.
Further, as shown in FIG. 13, a stepping motor 60 can be used as a drive source. In order to detect the shielding position of the shielding plate 55, a position sensor 59 for detecting the position of the holding member 56 is provided. Based on the position information detected by the position sensor 59, the stepping motor 60 can be driven and controlled via the gear train 61 connected to the holding member 56 to obtain the target shielding range and position. When the stepping motor 60 is used, fine change control of the position of the shielding plate 55 is possible. FIG. 13 is a perspective view of another specific example of variable shielding plate position.
Further, if the shield plate 55a fixed to the movable shield plate configuration is combined, it is possible to cope with the shielding range change shown in FIGS.

As described so far, it becomes possible to cope with different optimum separation conditions by using the shielding range and position change.
As one of them, it is conceivable to change the shielding range depending on the apparatus installation environment. Since the temperature of the fixing roller 51 is detected by the temperature detection member, it is maintained at a predetermined temperature. However, the optimum separation temperature changes due to the influence of the installation environment of the paper. In particular, it is conceivable that the optimum temperature for separation also changes because the paper strain changes due to the moisture content of the paper.
Therefore, temperature / humidity detection means may be provided in the apparatus, and the shielding range may be switched according to the detected value. For example, when the installation environment is high humidity, the paper is weak and is not favorable for separation. In such a case, it is conceivable to widen the shielding range as shown in FIG. 11 so as to be advantageous for separation. Conversely, when the installation environment is low humidity, it is effective to narrow the shielding range as shown in FIG. Here, the case of humidity that greatly contributes to separation has been described, but switching according to environmental temperature is also conceivable.

Similarly, it is conceivable to change the shielding range depending on the number of sheets to be passed. That is, the temperature of the pressure roller 52 rises by repeating the sheet passing. As a result, the fixing temperature range in which the fixing property and the separation property are compatible changes. Therefore, by correcting the position of the shielding plate 55 based on the number of sheets to be passed, it becomes possible to achieve both fixing property and separation performance regardless of the number of sheets to be passed.
For example, when the number of sheets to be passed is small, the temperature of the pressure roller 52 is low. At this time, heat from the pressure roller 52 cannot be obtained, and the amount of heat is insufficient from the viewpoint of fixability, and it is generally performed to compensate for the shortage of heat by increasing the set temperature at the initial stage of sheet passing. .
On the other hand, from the viewpoint of separation, when the temperature of the pressure roller 52 is low, a tendency to separate in the direction of winding around the fixing roller 51 has been confirmed, and it is advantageous to lower the set temperature contrary to the fixing property. . In the conflicting state at the beginning of paper feeding, the shielding range by the shielding plate 55 is widened as shown in FIG. 11 to increase the nip inlet temperature Tin and to keep the nip outlet temperature Tout low. It is possible to achieve both separations.

Further, as the number of sheets to be passed increases, there is a margin in fixing property and separability, so that the fixing temperature is lowered and the shielding plate 55 is narrowed as shown in FIG. it can. Further, in the case of a fixing device having a heating source in the pressure roller 52 and controlling the pressure roller temperature, the control position range can be changed by the pressure roller 52 control temperature.
The optimum position of the shielding plate during paper feeding is as described above. When the state of the apparatus is different, for example, the appropriate range position of the shielding plate during warm-up and standby is also different. At the time of warm-up, it is preferable to give all the heat amount of the heating source 53 to the fixing roller 51.

However, since the shielding plate itself prevents heat, the shielding range during warm-up is preferably the smallest range that can be set (for example, the state of FIG. 10). Further, the positional relationship between the temperature detecting means and the shielding plate 55 is detected. The detection means 54 is preferably located immediately before the shielding range of the shielding plate 55 because the temperature stored in the upstream is detected while the fixing roller 51 is rotating. . However, when the rotation of the fixing roller 51 during the warm-up is stopped, if it is in the vicinity of the shielding range of the shielding plate 55, the temperature of the portion where the temperature of the fixing roller 51 is slow due to the shielding is detected. It is better not to be too much. From this point of view, it is preferable that the shielding range of the shielding plate 55 at the time of warm-up is the smallest settable range.
Also, overshoot immediately after the end of warm-up is often a problem, but by increasing the shielding range of the shielding plate immediately before the end of warm-up, the temperature rise rate of the fixing roller 51 is slowed to reduce overshoot. Is also possible.
Further, it is preferable that the temperature of the fixing roller 51 is accurately detected with a uniform temperature distribution during standby. For this reason, it is better that the shielding range is as small as possible in the standby state (for example, the state of FIG. 10), and it is preferable that the shielding range is away from the temperature detection means. The reason is the same as when warming up.

As described above, it is possible to achieve separation of the sheet from the fixing roller 51 by controlling the nip outlet temperature Tout using the shielding plate 55. As a result, it has become possible to widen the range of conditions that can be separated using the non-contact separation means in the fixing device using the combination of the fixing roller 51 and the pressure roller 52 that could not be achieved by the conventional color machine. As a result, a non-contact separation member can be employed in a low-cost combination of the fixing roller 51 and the pressure roller 52, and high image quality can be achieved.
Although the case of one pressure roller has been described as an embodiment of the present invention, it is not specialized for this configuration. As another configuration, in the case of a plurality of pressure rollers, a case where a pressure belt is used in place of the pressure roller can be considered, but the same effect is considered to be obtained in any case.

Next, a specific embodiment in which a plurality of heating sources 53 are used will be described. FIG. 14 is a schematic configuration diagram of an embodiment in which a plurality of heating sources 53 are used.
Here, the case of using two heating sources will be described. As shown in FIG. 14A, a shielding plate 63 is provided between the heating source 53a and the heating source 53b. The purpose of providing a plurality of heating sources is to focus on the light distribution distribution of the heating source 53a and the heating source 53b, which supplements and uses power when a large amount of power is required, such as during warm-up. Mainly, the temperature is controlled so as to obtain an optimum temperature distribution in accordance with the size of the paper to be passed through, and the one that heats both ends of the paper passing width.
With reference to FIG. 14, the use in warming up and paper feeding in this embodiment will be described.
First, as shown in FIG. 14A, during the warm-up, the shielding range is reduced so as not to hinder the heat to the fixing roller 51. At this time, both the heat sources 53a and 53b are turned on. The heating source 53a is used both when warming up and the heating source 53b is dedicated to warming up.
Then, only the heating source 53a is controlled to be turned on when the paper is passed, and the heat source 53a used for passing the paper is basically disposed at a position far from the nip. As shown in FIG. The shielding range is increased, and as a result, the amount of heat from the heating source 53a can be prevented from being directly transmitted to the nip portion.

  Another embodiment specific to the case where a plurality of heating sources 53 are used will be described using the case where two heating sources are used. In order to further improve the effect of the shielding plate, one of the two heating sources is used to heat the edge of the maximum paper width, and the other is used to heat the area near the center of the paper. Configure as. In the vicinity of the center, that is, in the case of small size paper, it is the whole paper and is included from the paper center to the edge. By forcibly turning off the heating source at the timing when the leading edge of the paper is discharged from the nip, the effect of preventing the outlet temperature from rising by the shielding plate is compensated. At this time, the size of the paper to be passed is detected, and the one of the two heating sources that heats the edge of the paper intensively is turned off. For example, the end heating source is turned off when the size is large, and the central heating source is turned off when the size is small.

1 is a schematic configuration block diagram of an embodiment of a printer according to the present invention. FIG. It is a schematic block diagram of the separation resistance measuring apparatus in the printer shown in FIG. FIG. 6 is a graph showing a change in separation resistance between the fixing roller 51 and a sheet with respect to a fixing temperature. It is a graph which shows the relationship between separation resistance and fixing temperature. It is explanatory drawing which shows the concept of nip entrance temperature Tin and nip exit temperature Tout. It is a graph which shows the change of nip entrance temperature Tin and nip exit temperature Tout with respect to time. It is the schematic at the time of providing the shielding board 55a in the position which shields a nip part directly. 5 is a perspective view of a shielding plate 55a provided between the inside of the nip portion in the fixing roller 51 and a heating source 53. FIG. It is a schematic block diagram at the time of providing the shielding board 55a in the position moved to the upstream side. It is a schematic block diagram in the state where the shielding range where two shielding plates 55a and 55b are overlapped is narrow. It is a schematic block diagram of the state which moved the shielding board 55b and the shielding range was wide. It is a perspective view of the specific example of a shielding board position variable. It is a perspective view of the other specific example of a shielding board position variable. It is a schematic block diagram of embodiment at the time of using the multiple heating source 53. FIG.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Intermediate transfer belt, 1a ... Drive roller, 1b ... Driven roller, 2Y, 2C, 2M, 2K ... Toner bottle, 3 ... Discharge roller, 4 ... Secondary transfer roller, 5 ... Fixing device, 5 ... Transfer counter roller , 6 ... Registration roller, 7 ... Paper feeding roller, 8 ... Paper feeding cassette, 9 ... Optical writing unit, 10Y, 10C, 10M, 10K ... Developing device, 11Y, 11C, 11M, 11K ... Primary transfer device, 12 ... Intermediate transfer member cleaning device, 17Y, 17C, 17M, 17K ... charging device, 21Y, 21C, 21M, 21K ... photosensitive member, 41 ... separation claw, 42 ... load cell, 51 ... fixing roller, 52 ... pressure roller, 53 ... Heat source, 54 ... temperature detection control means, 55 ... shielding plate, 55a ... shielding plate, 55b ... shielding plate, 56 ... holding member, 57 ... solenoid, 58 ... elastic member, 59 ... position sensor, 60 ... Stepping motor, 61 ... gear train, 63 ... shield plate, 101Y, 101C, 101M, 101K ... image forming unit

Claims (9)

Nip which incorporates a heat source, comprising: a rotatable fixing roller for heating the interior by heat source and a pressure roller for pressing and fixing rollers and pressing, is formed by the heating roller and the fixing roller A fixing device that heat-presses and fixes unfixed paper in a section,
Inside the fixing roller, it is disposed between the front Stories heat source and the nip portion includes a shielding member for shielding the radiant heat radiated toward from said heat source to said nip,
The shielding member is movable in the circumferential direction in the fixing roller, and a region heated by the radiant heat in the nip portion can be changed by changing a position with respect to the nip portion. A fixing device. The temperature of the fixing roller required for fixing an unfixed image is T1, and the temperature of the fixing roller at which the separation resistance when the sheet is separated from the fixing roller after passing through the nip portion is equal to or less than a predetermined value. When T2 is set, the temperature Tin of the fixing roller immediately before the nip formed by the fixing roller and the pressure roller is controlled to be equal to or higher than T1, and the position of the shielding member is controlled by controlling the position of the shielding member. Temperature control means for controlling the temperature so that the temperature Tout of the fixing roller immediately after the nip portion is T2 or less and T1> T2.
The fixing device according to claim 1, further comprising:   The shielding member includes an auxiliary shielding member overlaid on the shielding member,
  The fixing device according to claim 1, wherein the shielding range of the shielding member can be changed by the auxiliary shielding member moving in the circumferential direction in the fixing roller.   The fixing device according to claim 3, wherein a position and a shielding range of the shielding member are selected according to a plurality of paper conveyance speeds.   The fixing device according to claim 3, wherein a position and a shielding range of the shielding member are selected according to an installation environment of the fixing device.   The fixing device according to claim 3, wherein a position and a shielding range of the shielding member are changed according to the number of sheets that are passed.   4. The fixing device according to claim 3, wherein the position and the shielding range of the shielding member are selected so as to be different for a warm-up operation, a standby time, and a sheet passing time of the fixing device.   The fixing device according to claim 1, wherein a non-contact separating unit is used as the sheet separating unit from the fixing roller.   An image forming apparatus comprising the fixing device according to claim 1.

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