JP7091973B2 - Fixing device, image forming device and fixing method - Google Patents

Description

The present invention relates to a fixing device, an image forming device including the fixing device, and a fixing method.

In a fixing device used in an image forming apparatus such as a copier, a printer, or a facsimile, a rotating pressing member is pressed against a rotating fixing member to form a fixing nip, and the pressing member is driven and rotated. , A recording material called transfer paper, recording paper, etc. is sandwiched and conveyed to the fixing nip, and the toner image is fixed to the recording material by the action of heat and pressure.

However, since the rollers constituting the fixing member and the pressure member use an elastic material at least on the surface side to form the fixing nip, the outer diameter fluctuates due to thermal expansion and the hardness deteriorates with time. / As the outer diameter shrinks, the radius from the center of the roller to the fixing nip fluctuates. Therefore, there is a problem that it is difficult to keep the fixing line speed constant only by driving the rollers at a constant rotation. Further, since the fixing nip is formed by the rollers collapsing with each other, there is a problem that the true radius from the center of the roller to the fixing nip cannot be obtained only by measuring the diameter / outer diameter of the rollers.

Further, in a belt fixing type fixing device in which a belt is stretched by a fixing roller and a heating roller and the belt is rotated by a pressure roller from the outer peripheral side of the belt, heat is applied from the heating roller to the fixing roller through the belt and at the same time. The fixing roller is rotated by pressing the pressure roller against the fixing roller via the belt, and the drive is conventionally on the pressure member side (non-image surface side). Therefore, a very slight linear velocity difference (small linear velocity difference) occurs between the fixing member side, which is the driven side, and a gloss step (wax in the toner remains on the belt side, which disturbs the image). ) Occurred. In order to improve this problem, it is necessary to eliminate this minute linear velocity difference between the fixing member side and the pressurizing member side, and one means is to drive the fixing member side to eliminate the linear velocity difference from the image. However, in any case, it is inevitable that a slight slip may occur between the belt and the belt.

Therefore, in order to prevent printing defects caused by the difference in transport speed due to the temperature difference between the members, Patent Document 1 detects and detects the temperature difference between the core metal of the fixing roller and / or the core metal of the pressure roller. It was proposed to adjust the linear velocity according to the temperature applied.

However, as described above, the radius from the center of the roller to the fixing nip fluctuates due to the fluctuation of the outer diameter due to thermal expansion and the deterioration of hardness / reduction of the outer diameter over time. / There is a problem that it is difficult to keep the fixing linear speed constant only by controlling the linear velocity by detecting the temperature of the pressurizing roller.

The subject of the present invention is to maintain a stable fixing line speed at all times without being affected by outer diameter fluctuations due to thermal expansion and outer diameter fluctuations due to hardness deterioration over time, and by pulling or loosening the recording material. The purpose is to avoid abnormal images that occur and to secure high-quality images.

In order to solve the above problems, the present invention is a fixing device in which a fixing nip is formed by a pair of rotating bodies having at least an elastic layer on the surface thereof, and one of the pair of rotating bodies is driven by a motor. A pair of a first detecting means for detecting the outer diameter of one of the rotating bodies in a non-crushed state and a second detecting means for detecting the outer diameter of the other rotating body in a non-crushed state. We propose a fixing device having a third detecting means for detecting the distance between the axes of the rotating body of the above, and a means for controlling the rotation speed of the motor according to the detection result of these detecting means.

According to the present invention, it is possible to maintain a stable fixing line speed at all times without being affected by outer diameter fluctuations due to thermal expansion and outer diameter fluctuations due to deterioration of hardness over time, and it is possible to pull the recording material. It is possible to avoid abnormal images caused by slack and secure high-quality images.

It is a block diagram which shows schematicly about the fixing apparatus which concerns on one Embodiment of this invention, in particular with respect to the characteristic structure of the invention. It is shown that the pressure roller radius Rr of the nip portion differs depending on the combination of the hardness states of the fixing roller and the pressure roller. FIG. 2a shows a combination in which the pressure roller is softer than the fixing roller, and FIG. 2b. Is a combination in which the pressure roller is harder than the fixing roller. It is a schematic diagram which shows the image forming apparatus provided with the fixing apparatus of FIG.

FIG. 1 shows an outline of a belt fixing type fixing device 20 according to an embodiment of the present invention. The fixing belt 21 is supported and stretched by a fixing roller 22, a heating roller 23, and a tension roller 24 that form one of a pair of rotating bodies. In the fixing belt 21, the pressurizing roller 25 constituting the other of the pair of rotating bodies that abuts on the outer peripheral side of the fixing belt 21 is rotationally driven by a motor as a driving means (a motor for determining / fixing the fixing line speed). By doing so, it runs in rotation. That is, the drive is on the pressure member side. Then, when the fixing belt 21 rotates, the fixing roller 22 also rotates around the fixing belt 21.

The fixing belt 21 has a two-layer structure in which an elastic layer such as a silicone rubber layer (300 to 500 μm) is formed on a base material such as nickel, stainless steel, or polyimide. The fixing roller 22 has an elastic layer made of, for example, silicone rubber, on a metal core metal. The heating roller 23 is composed of a hollow roller made of a metal such as aluminum or iron, and is provided with a fixing heater as a heat source inside. Then, the heating roller 23 is heated by the fixing heater, the fixing belt 21 is heated by the heating roller 23, and the fixing roller 22 is heated by the heated fixing belt 21.

The temperature of the fixing belt 21 or the fixing roller 22 heated by the heating roller 23, particularly the surface temperature, is detected by the temperature detecting element 41 which is the first temperature detecting means arranged on the outer peripheral side, and is provided in the image forming apparatus main body. The control unit controls the heater for fixing so that the temperature of the fixing roller 22 becomes a predetermined set temperature based on the output value of the temperature detecting element. A temperature detecting element 42, which is a second temperature detecting means for detecting the temperature of the pressurizing roller 25, is also provided.

Similar to the fixing roller 22, the pressure roller 25 having an elastic layer on the metal core metal is provided so as to face the fixing roller 22 via the fixing belt 21, and is well-known for pressure removal during the fixing operation. By the pressure mechanism, pressure is applied to the fixing roller 22 via the fixing belt 21, both rollers are crushed, and the fixing nip N is formed by the fixing roller 22 and the pressure roller 25 via the fixing belt 21. Will be done.

Paper, which is a recording material carrying an unfixed toner image, is carried into the fixing device 20 and passes through the fixing nip N. At that time, the toner image is melt-fixed by the fixing nip N controlled to a predetermined temperature.

In the fixing device having the above configuration, the motor for fixing is generally controlled to maintain a constant rotation speed, so that the pressurizing roller 25 rotates at a constant rotation speed accordingly. .. The paper transport speed when the paper passes through the fixing nip N is determined by the radius Rr at the fixing nip of the pressure roller 25 and the rotation speed of the pressure roller 25.

However, the radius Rr at the fixing nip of the pressure roller 25 changes every moment depending on the outer diameter and hardness (crushing degree) of the fixing roller 22 and the pressure roller 25. Further, the fixing roller 22 is thermally affected by the heating roller 23 heated by the heater on the fixing member side through the fixing belt 21. Therefore, depending on the temperature of the fixing roller 22, the elastic layer expands thermally, and as a result, the outer diameter of the fixing roller 22 also changes, and the hardness also changes. The same phenomenon occurs in the pressure roller 25 which also has an elastic layer on the surface, and the outer diameter and hardness of the pressure roller 25 also change due to the thermal influence.

Therefore, in the present embodiment, the fixing device 20 is provided with a detecting means for detecting the outer diameter and the amount of crushing of each roller. That is, the first detecting means 43 for detecting the diameter / outer diameter (2R ₁ ) of the fixing roller 22 in the non-crushed state, the diameter / outer diameter (2R ₂ ) of the pressure roller 25 in the non-crushed state. ), The second detection means 44, the distance between the axes of the fixing roller 22 and the pressure roller 25, that is, the mutual center distance in the state where both rollers are most crushed by the fixing nip N. The detection means 45. If an optical positioning means is used as these detecting means, the detection can be performed in a non-contact manner, and the outer diameter information can be obtained without damaging the fixing roller 22 or the pressure roller 25.

The detection results of the distance between the axes of the fixing roller 22 and the pressure roller 25 and the outer diameters of the fixing roller 22 and the pressure roller obtained by using these detection means are sent to the control unit provided in the image forming apparatus. It is used to control the rotation speed of the motor for fixing. That is, if the elastic layers of the fixing roller 22 and the pressure roller 25 are made of the same material, the motor can be measured by measuring the distance between the axes of both rollers and the outer diameter of each roller, which change as a result of thermal expansion. The radius from the center of the pressurizing roller 25 driven by rotation to the fixing nip can be calculated, and the rotation speed of the motor can be appropriately controlled. However, when the elastic layers of the fixing roller 22 and the pressure roller 25 are made of different materials and therefore the hardness is different, the actual measurement of the inter-axis distance and the outer diameter is not sufficient for controlling the rotation speed of the motor. do not have.

FIG. 2 shows how the pressure roller radius Rr at the fixing nip differs depending on the combination of the hardness states of the fixing roller and the pressure roller. FIG. 2a shows a case where the fixing roller is hard and the pressure roller is soft. When the inter-axis dimension is X ₁ , the soft pressure roller has a large amount of crushing, and as a result, the radius Rr ₁ has a small value. FIG. 2b shows a case where the fixing roller is soft and the pressure roller is hard. The inter-axis dimension is X ₁ which is the same as in FIG. 2a, but the hard pressure roller has a small amount of crushing, and as a result, the radius Rr ₂ has a large value. In this way, when the fixing nip is formed from a pair of rotating bodies having an elastic layer on each surface, each is crushed according to the relative hardness. Therefore, in order to know the pressure roller radius Rr, each hardness is obtained. You also need to know the information. It is possible to calculate Rr by knowing the outer diameter, hardness, and inter-axis dimensions.

Since the outer diameter and hardness change according to the temperature (effect of thermal expansion), a temperature detecting means is required. However, in the present embodiment, as described above, the temperature of the fixing roller 22 and the pressure roller 25 is adjusted. The first and second temperature detecting elements 41 and 42 that detect the temperature can grasp each temperature state. Examples of the temperature detecting element include a contact type thermistor in order to detect the surface temperature of the fixing roller 22 and the pressure roller 25. Further, in order to prevent sliding scratches due to contact, a temperature detecting means such as a non-contact thermistor or a thermopile may be used.

表１から、加熱すると、外径及び硬度が変化していく様子が分かる。 As an example, Table 1 shows the changes in the outer diameter and hardness of the fixing roller and the pressurizing roller according to the temperature.

From Table 1, it can be seen that the outer diameter and hardness change when heated.

Table 2 shows the change in the radius of the pressure roller when the hardness of the fixing roller and the pressure roller are combined.

Table 2 shows the evaluation data when the inter-axis dimension X ₁ has a certain constant value and a constant temperature. It can be seen that Rr has a different value even if the inter-axis dimension X ₁ is constant, because the crushing method of both is different depending on the combination of the hardness of the fixing roller and the pressure roller forming the nip. If Rr becomes small, the target fixing line speed can be achieved by reducing the motor rotation. On the contrary, when Rr is large, the target fixing line speed can be obtained by increasing the motor rotation. When the fixing roller and the pressure roller are heated and the elastic layer expands thermally, the inter-axis dimension X ₁ changes (becomes larger), and the hardness of both changes accordingly. For example, it is possible to calculate the radius Rr of the pressure roller in various states.

Therefore, if the motor that rotationally drives the pressurizing roller 25, that is, the rotation speed of the motor for fixing is controlled in consideration of the information tabulated in advance, a more appropriate fixing line speed can be realized. Can be done.

The fixing device according to the present embodiment is a belt fixing method, and a fixing roller 22 having a relatively large heat capacity, which heats a fixing belt 21 having a small heat capacity from a heating roller 23 and forms a fixing nip N by the amount of heat, further. After the pressure roller 25 is also warmed, heat is applied to the toner by the fixing nip N, so that it takes time to warm up. In order to avoid this, a heating element (for example, an infrared heater) may be arranged inside the hollow core metal of the pressure roller 25 to heat the pressure roller 25 from the center of the pressure roller 25. In this case, the pressurizing roller 25 continues to be warmed in the "standby state" waiting for the paper passing job signal. At this time, the pressure roller 25 has the highest temperature in the central portion where the heating element is located and the lowest temperature in the surface layer. Then, when a paper passing job signal is input, a “warm-up state” is set, and the surface temperature of the pressurizing roller 25 also rises due to heat received from the fixing belt side. Since the temperature of the elastic layer of the pressure roller 25 may differ in the thickness direction depending on the situation, the temperature of the pressure roller 25 can be detected at a plurality of locations (for example, near the surface and the core metal) to detect the pressure roller 25. It is possible to know the expanded state of the elastic layer in more detail. The same can be said for the fixing roller 22 that does not have a heating element inside (for example, even if the fixing roller temperature is the same immediately after warming up and after continuous paper passing, the internal temperature distribution of the elastic layer, and therefore the elastic layer. The state of thermal expansion is different). By adding such a difference in the expansion state of the elastic layer in the thickness direction to the factor of controlling the rotation speed of the motor for fixing, it is possible to further optimize the fixing line speed. Further, the same applies to the thermal roller type fixing device.

Finally, the image forming apparatus 1 provided with the fixing apparatus 20 described above will be described. The image forming apparatus 1 is a color laser printer, and four image forming portions 4Y, 4C, 4M, and 4K are juxtaposed along the spreading direction of the intermediate transfer belt 30 in the center of the printer body. There is. Each image forming unit 4Y, 4C, 4M, 4K accommodates developers of different colors of yellow (Y), cyan (C), magenta (M), and black (K) corresponding to the color separation components of the color image. Other than that, it has the same configuration.

Specifically, each image forming unit 4Y, 4C, 4M, 4K constituting the image station includes a drum-shaped photoconductor 5 as a latent image carrier and a charging device 6 for charging the surface of the photoconductor 5. I have. Further, it includes a developing device 7 that supplies toner to the surface of the photoconductor 5, a cleaning device 8 that cleans the surface of the photoconductor 5, and the like. In FIG. 3, reference numbers are assigned only to the photoconductor 5, the charging device 6, the developing device 7, and the cleaning device 8 included in the black image forming unit 4K, and are omitted in the other image forming units 4Y, 4C, and 4M. is doing.

Below the image forming portions 4Y, 4C, 4M, and 4K, an exposure apparatus 9 for exposing the surface of the photoconductor 5 is arranged. The exposure apparatus 9 has a light source, a polygon mirror, an f−θ lens, a reflection mirror, and the like, and irradiates the surface of each photoconductor 5 with laser light based on image data.

A transfer device 3 is arranged above the image forming portions 4Y, 4C, 4M, and 4K. The transfer device 3 includes an intermediate transfer belt 30 as a transfer body, four primary transfer rollers 31 as primary transfer means, and a secondary transfer roller 36 as secondary transfer means. Further, the transfer device 3 includes a secondary transfer backup roller 32, a cleaning backup roller 33, a tension roller 34, and a belt cleaning device 35.

The intermediate transfer belt 30 is an endless belt and is stretched by a secondary transfer backup roller 32, a cleaning backup roller 33, and a tension roller 34. Here, the secondary transfer backup roller 32 is rotationally driven so that the intermediate transfer belt 30 orbits (rotates) in the direction indicated by the arrow in the figure.

Each of the four primary transfer rollers 31 sandwiches an intermediate transfer belt 30 with each photoconductor 5 to form a primary transfer nip. Further, a power supply of the printer main body is connected to each primary transfer roller 31, and a predetermined direct current voltage (DC) and / or AC voltage (AC) is applied to each primary transfer roller 31. ..

The secondary transfer roller 36 sandwiches the intermediate transfer belt 30 with the secondary transfer backup roller 32 to form a secondary transfer nip. Further, similarly to the primary transfer roller 31, the power supply of the printer main body is connected to the secondary transfer roller 36, and a predetermined direct current voltage (DC) and / or AC voltage (AC) is applied to the secondary transfer roller 36. It is supposed to be done.

The belt cleaning device 35 has a cleaning brush and a cleaning blade arranged so as to be in contact with the intermediate transfer belt 30.
A bottle accommodating portion 2 is provided on the upper portion of the printer main body, and four toner bottles 2Y, 2C, 2M, and 2K accommodating replenishing toner are detachably attached to the bottle accommodating portion 2. As is well known, a replenishment path is provided between each toner bottle 2Y, 2C, 2M, 2K and each developing device 7, and each development is performed from each toner bottle 2Y, 2C, 2M, 2K via this replenishment path. Toner is replenished to the device 7.

On the other hand, at the lower part of the printer main body, a paper feed tray 10 containing the paper P as a recording material, a paper feed roller 11 for carrying out the paper P from the paper feed tray 10, and the like are provided. Further, as is well known, a manual paper feed mechanism may be provided.

A transport path R for passing the paper P from the paper feed tray 10 through the secondary transfer nip and discharging the paper P to the outside of the apparatus is provided in the printer main body. In the transport path R, a pair of resist rollers 12 as transport means for transporting the paper P to the secondary transfer nip are arranged on the upstream side in the paper transport direction from the position of the secondary transfer roller 36.

Further, the fixing device 20 described above is arranged on the downstream side in the paper transport direction from the position of the secondary transfer roller 36. Further, a pair of paper ejection rollers 13 for ejecting the paper P to the outside of the apparatus are provided on the downstream side of the transport path R in the paper transport direction with respect to the fixing device 20. Further, a paper ejection tray 14 for stocking the paper P ejected outside the apparatus is provided on the upper surface of the printer main body.
Since the basic operation of the printer as described above is well known, the description thereof will be omitted.

20 Fixing device 21 Fixing belt 22 Fixing roller 23 Heating roller 25 Pressurizing roller 43 First detection means 44 Second detection means 45 Third detection means

JP-A-2015-227978

Claims (7)

A fixing device in which a fixing nip is formed by a pair of rotating bodies having at least an elastic layer on the surface thereof, and one of the pair of rotating bodies is driven by a motor, and the one rotating body is not crushed. A first detecting means for detecting the outer diameter of the other rotating body, a second detecting means for detecting the outer diameter of the other rotating body without crushing, and a second detecting means for detecting the distance between the axes of the pair of rotating bodies. A fixing device comprising 3 detection means and means for controlling the rotation speed of the motor according to the detection result of these detection means. A temperature detecting means for detecting the temperature of each of the pair of rotating bodies is provided, and the temperature of each rotating body detected by the temperature detecting means and the hardness of each rotating body are taken into consideration to obtain the one rotating body. The fixing device according to claim 1, wherein a radius from the center to the fixing nip is calculated, and the rotation speed of the motor is controlled accordingly. The fixing device according to claim 2, wherein the temperature detecting means for detecting the temperature of each of the pair of rotating bodies detects the temperature at a plurality of points in the thickness direction of the elastic layer. The fixing device according to claim 1, wherein the first, second, and third detection means are optical positioning means. The other rotating body supports and stretches a belt, and when the one rotating body is rotationally driven by the motor, the other rotating body rotates with the other rotating body via the belt. The fixing device according to any one of 1 to 4. An image forming apparatus comprising the fixing apparatus according to any one of claims 1 to 5. A method of forming a fixing nip by a pair of rotating bodies having at least an elastic layer on the surface thereof, and controlling the fixing linear speed of a fixing device in which one of the pair of rotating bodies is driven by a motor. To detect the outer diameter of the rotating body without crushing, to detect the outer diameter of the other rotating body without crushing, to detect the distance between the axes of these pair of rotating bodies, these A method characterized by controlling the fixing line speed by changing the rotation speed of the motor according to the detection results of outer diameter detection and inter-axis distance detection.

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