JP4834247B2 - Fixing device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a fixing device for fixing to the transfer material by heating and melting the unfixed toner image.
[0002]
[Prior art]
The configuration of a conventional fixing device is shown in FIG . As shown in FIG. 3 , 1 is a fixing roller, the core metal is pipe-shaped aluminum, and the surface layer is provided with a release layer by PTFE or PFA coating or resin tube coating. A pressure roller 2 is provided with a rubber layer 13 as an elastic layer and a release layer 14 of a PFA tube on an iron cored bar 12. The pressure roller 2 is in pressure contact with the fixing roller 1. A halogen heater 3 warms the fixing roller 1 from the inside. Reference numeral 42 denotes a temperature detection contact thermistor which changes the temperature of the fixing roller 1 into an electric signal and sends it to the main body control unit 55 (see FIG. 4 ). The main body control unit 55 controls lighting of the halogen heater 3 based on the output value so as to keep the fixing roller 1 at a predetermined temperature.
[0003]
Reference numeral 8 denotes an inlet guide that guides the paper to the fixing nip, and 4 denotes a separation claw for separating the paper from the fixing roller 1. Reference numeral 5 denotes a separation guide for separating the paper from the pressure roller 2, but since the pressure roller 2 usually has an elastic layer of about 2 mm or more, the contact roller damages the pressure roller 2. Therefore, it is often a non-contact type separation guide. The distance between the tip of the separation guide 5 and the pressure roller 2 is generally about 0.5 mm or less.
[0004]
Reference numeral 6 denotes a paper discharge sensor flag . When paper comes out from the fixing nip, it is pushed by the paper and moves as indicated by an arrow in FIG . This movement is read by the photo sensor 7 to recognize the passage of the paper. In FIG. 3 , 9 and 10 indicate fixing exterior covers, and 11 indicates the entire fixing device.
[0005]
FIG. 4 shows the configuration of the image forming apparatus provided with the fixing device 11. As shown in FIG. 4 , 54 is a process cartridge comprising a drum charger, a developer, and a cleaner, 53 is an exposure device, 15 is a transfer roller, 16 and 20 are paper transport guides, 17 is a paper cassette, and 18 is a paper feed roller. , 19 is a conveyance roller, 21 is a paper discharge tray, and 23 is a branching guide for switchback of double-sided printed paper. 24 is a movable flapper for sending the fixed paper to the double-sided switchback, to the paper discharge tray, or for branching. The paper fed by the paper feed roller 18 is transferred to the toner image formed by the exposure device 53 and the cartridge 54 by the action of the transfer roller 15, sent to the fixing device 11 through the guide 16, and on the paper. The toner image is fixed by heating and pressing at the nip between the fixing roller and the pressure roller. The temperature of the fixing roller is 200 ° C., and the pressure of the pressure roller is about 20 kg.
[0006]
In the case of single-sided printing, the paper on which the toner image is fixed is sent as it is to the paper discharge tray 21 via the flapper 24.
[0007]
The paper used for double-sided recording is sent to the switchback branch guide 23 by the flapper 24. When the trailing edge of the paper passes the branch guide 23, the paper is fed in the opposite direction, so that the leading and trailing edges of the paper are switched and the recording surface is reversed. The paper is again subjected to the image forming process, fixed, and then discharged to the paper discharge tray 21.
[0008]
Since double-sided recording is performed in the above-described steps, the surface on the rear end side of the first surface is the back surface on the front end side when recording on the second surface.
[0009]
[Problems to be solved by the invention]
However, the conventional example has a problem in that paper is wound around the pressure roller during double-sided recording and cannot be removed.
[0010]
More specifically, as shown in FIG. 5, when a large area is recorded on the rear end surface in the first recording, the image becomes the back surface on the second front end in double-side recording. At this time, the toner on the first surface fixed on the paper is melted again in the fixing nip, becomes sticky, and sticks to the pressure roller 2. Further, when the recording on the second side has a smaller area than the first side, the paper is not attached to the fixing roller 1 but only to the pressure roller 2. This phenomenon is likely to occur when recording on the first side is performed near the edge of the paper.
[0011]
For example, the diameter of the fixing roller 1 is 50 mm, if the diameter of the pressure roller 2 is 40 mm, within 10mm in paper 64 g / cm ^2, when performing solid black recording within 8mm in paper 75 g / cm ^2, FIG. As shown in FIG. 5, the leading edge of the paper slips into the lower side of the non-contact separation guide 5, and separation becomes impossible. In FIG. 5 , 25 is paper, and 26 is toner recorded on the first side. If the fixing device 11 is further operated in this state, the paper 25 is completely wound around the pressure roller 2 and cannot be removed.
[0012]
This separation failure of the paper from the pressure roller 2 is likely to occur when the diameter of the pressure roller that reduces the effect of curvature separation due to paper stiffness is large, or when a filler such as carbon is applied to the surface layer of the pressure roller. This is likely to occur when the release property of the surface of the pressure roller is reduced.
[0013]
Accordingly, an object of the present invention is to prevent fixing defects caused by winding of paper that is difficult to remove onto the pressure roller and winding of paper on the pressure roller.
[0014]
[Means for Solving the Problems]
Configuration of the present invention for achieving the above object, a heat source, a fixing roller that is heated by said heat source, a fixing nip portion formed together with the fixing roller, a pressure roller which is not directly heated by the heat source, before Symbol fixing A drive control means for controlling the rotation of the roller and the pressure roller; and a temperature control means for controlling a heat source so that the fixing roller is kept at a predetermined temperature. In a fixing device for fixing an unfixed toner image to a transfer material while nipping and conveying the transfer material carrying the toner , the power supply means for supplying power to the pressure roller is opposed to the surface of the pressure roller in a non-contact state. An electrode and current detection means that is electrically connected to the electrode and detects a current flowing through the electrode, and the output of the current detection means is when the transfer material is normally conveyed If a different output, the drive control means is characterized by stopping the rotation of the fixing roller and the pressure roller.
[0015]
With the above-described configuration, it is possible to prevent fixing defects caused by winding of the transfer material that is difficult to remove onto the pressure roller and winding of the transfer material around the pressure roller.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the drawings. However, the dimensions, materials, shapes, and relative arrangements of the components described in the following embodiments should be appropriately changed according to the configuration of the apparatus to which the present invention is applied and various conditions. As long as there is no specific description, it is not the meaning which limits the scope of the present invention only to them.
[0017]
[First Embodiment]
The image forming apparatus including the fixing device according to the first embodiment will be described in detail with reference to the drawings. The overall schematic structure image forming apparatus are the same as those described with reference to FIG. 4, a detailed description thereof will be omitted. FIG. 1 is a cross-sectional view of a fixing device according to a first embodiment of the present invention . Among the reference numerals in FIG. 1, the same reference numerals as those in FIG. 4 denote the same members.
[0018]
In FIG. 1, 33 is a pressure roller, and the surface release layer 28 is a PFA tube to which carbon is added to make the surface resistivity 10 ⁴ Ω or less. In this embodiment, the diameter of the pressure roller 33 is 40 mm, and the outer diameter of the fixing roller 1 is 50 mm. The fixing roller 1 is formed by providing an insulating release layer 35 having a thickness of 50 μm on an aluminum cored bar 34 having a thickness of 3 mm. Since the core metal 34 of the fixing roller 1 is electrically grounded, the surface potential is 0V. The release layer 35 on the surface layer of the fixing roller 1 is obtained by heat-melting and bonding an insulating PFA tube having a thickness of 50 μm.
[0019]
Reference numeral 27 denotes a power supply brush that is in contact with the pressure roller 33 in a non-sheet passing region. The power supply brush 27 is connected to a high voltage power source 29. The output voltage of the high voltage power supply 29 is 1000 V, and this potential appears on the surface of the pressure roller 33.
[0020]
For this reason, the potential difference between the fixing roller 1 and the pressure roller 33 is 1000 V, and this potential difference can prevent the fixing offset in which the toner on the paper is transferred to the fixing roller 1.
[0021]
The fixing offset is a phenomenon in which the toner is transferred to the fixing roller before the fixing nip. The toner transferred to the fixing roller partially remains on the fixing roller even after passing through the nip due to the unevenness of the paper, and is transferred to the paper and becomes a smudged image at the next round.
[0022]
In FIG. 1, reference numeral 30 denotes a current detection static elimination needle as an electrode member, 32 denotes a current detection unit as current detection means, and 31 denotes a high voltage power source. The static elimination needle 30 is a 0.2 mm thick stainless steel sheet having a sharp tip, and is attached to the pressure roller 33 at a distance of 2 mm. The static elimination needle 30 is applied with a voltage of −1000 V from the high voltage power supply 31. A current detector 32 is provided between the static elimination needle 30 and the power source 31 and detects a current flowing from the pressure roller 33 to the static elimination needle 30 due to discharge.
[0023]
The current detection unit 32 is connected to a main body control unit 55 as a control unit, and controls the rotational drive of the fixing device 11 based on the output value.
[0024]
The longitudinal positional relationship of the fixing device will be described with reference to FIG. As shown in FIG. 2, the power supply brush 27 that supplies a voltage to the pressure roller 33 contacts the pressure roller 33 outside the sheet passing area. The reason is to prevent the toner from adhering to the power supply brush 27 to cause poor conduction, or the toner adhering to the power supply brush 27 from adhering again to the pressure roller 33 and becoming soiled on the paper. The pressure separation guide 5 is provided in the paper passing area. The static elimination needle 30 is provided in the center of the paper passing portion on the downstream side of the pressure separation guide 5. The reason is that the image forming apparatus of the present embodiment supports several types of paper sizes, the paper passing reference is the center, and the detection of paper wrapping corresponds to all paper sizes.
[0025]
Next, the operation will be described with reference to FIGS. A potential of +1000 V is generated on the surface of the pressure roller 33. A static elimination needle 30 to which a voltage of −1000 V is applied with a gap of 2 mm is disposed opposite to the pressure roller. For this reason, a current of about 5 μA normally flows through the static elimination needle 30. This current value varies depending on the shape of the tip of the static elimination needle 30, the distance between the static elimination needle 30 and the pressure roller 33, the surface resistance of the pressure roller 33, and the applied bias. If these conditions are constant, the current value is almost constant. is there. This current value is detected by the current detector 32. If the current value is 5 μA, it is not regarded as abnormal.
[0026]
On the other hand, when paper is stuck on the pressure roller 33 and cannot be separated by the separation guide 5, the following operation is performed. The paper that has passed through the pressure separation guide 5 reaches the facing portion between the pressure roller 33 and the charge removal needle 30 while being stuck to the pressure roller 33. Then, since a resistor (paper) enters between the static elimination needle 30 and the pressure roller 33, the current flowing through the static elimination needle 30 is extremely reduced. Since the paper (resistor) that has passed through the fixing nip is heated, moisture evaporates and resistance increases. For this reason, the current difference between when there is paper and when there is no paper is large, and it is easy to detect.
[0027]
For example, when 64 g / cm ² plain paper as a transfer material is wound, the current value is 0.5 μA or less.
[0028]
In such a case, the rotation driving of the pressure roller 33 is stopped, and an instruction is given to prompt the user to remove the jammed paper in the operation unit or the like of the image forming apparatus.
[0029]
Note that the current value for determining that the paper is wound around the pressure roller 33 is not fixed to 0.5 μA, but may be determined according to the configuration conditions of the apparatus, the type of paper to be used, and the like.
[0030]
With the configuration described above, when paper is wound around the pressure roller, the fixing device can be stopped immediately, and occurrence of paper jam that is difficult to process can be prevented.
[0031]
Further, since the charge eliminating needle 30 is not in contact with the pressure roller 33, any type of paper can be used in a fixing device that passes paper of different sizes.
[0032]
Note that the rotation drive of the fixing device may not only be stopped, but the paper may be rotated backward to eject the paper from the fixing device to the upstream side. As a result, there is an effect that the jam processing can be more easily performed.
[0033]
[Other Embodiments]
In the above-described embodiment, the printer is exemplified as the image forming apparatus. However, the present invention is not limited to this, and may be another image forming apparatus such as a copying machine or a facsimile machine. The same effect can be obtained by applying the present invention to the apparatus.
[0034]
Furthermore, the same effect can be expected when the present invention is applied not only to an image forming apparatus capable of forming a monochrome image but also to an image forming apparatus capable of forming a color image.
[0035]
【The invention's effect】
As described above, according to the present invention, it is possible to prevent the transfer material from being easily wound around the pressure roller, and to prevent the fixing failure caused by the transfer material being wound around the pressure roller.
[0036]
Further, since the detection means is not in contact with the pressure roller, it is possible to always monitor the winding of the transfer material around the pressure roller. If the transfer material is wound around the pressure roller, it is immediately detected. and stop the fixing device, it is possible to prevent the process difficult jams.
[Brief description of the drawings]
Figure 1 is a cross-sectional view of a cross-sectional view FIG. 2 is a perspective view of a fixing device of the first embodiment FIG. 3 is a cross-sectional view FIG. 4 the image forming apparatus of a conventional fixing device of the fixing device of the first embodiment [ FIG. 5 is an explanatory diagram of a conventional image forming apparatus in which a pressure roller is wrapped around paper.
DESCRIPTION OF SYMBOLS 1 ... Fixing roller 2 ... Pressure roller 3 ... Halogen heater 4 ... Separation claw 5 ... Separation guide 6 ... Discharge sensor flag 7 ... Photo sensor 8 ... Entrance guide 9, 10 ... Fixing exterior cover 11 ... Fixer 12 ... Core metal DESCRIPTION OF SYMBOLS 13 ... Rubber layer 14 ... Release layer 15 ... Transfer roller 16, 20 ... Paper conveyance guide 17 ... Paper cassette 18 ... Paper feed roller 19 ... Conveyance roller 21 ... Paper discharge tray 22 ... Image forming apparatus 23 ... Branch guide 24 ... Flapper 25 ... paper 26 ... toner 27 ... power supply brush 28 ... release layer 29 ... high-voltage power supply 30 ... static elimination needle 31 ... high-voltage power supply 32 ... current detector 33 ... pressure roller 34 ... core metal 35 ... release layer 42 ... contact type Thermistor 53... Exposure device 54... Process cartridge 55.

Claims (1)

Heat source and a fixing roller heated by said heat source, said fixing nip portion is formed with the fixing roller, a pressure roller which is not directly heated by a heat source, a drive control for controlling the rotation of the pre-Symbol fixing roller and the pressure roller And a temperature control means for controlling a heat source so that the fixing roller is kept at a predetermined temperature, and the unfixed toner while nipping and conveying the transfer material carrying the unfixed toner image at the fixing nip portion. In a fixing device for fixing an image to a transfer material,
A power supply means for supplying power to the pressure roller, an electrode facing the surface of the pressure roller in a non-contact state, and a current detection for detecting a current flowing through the electrode that is electrically connected to the electrode And the drive control means stops the rotation of the fixing roller and the pressure roller when the output of the current detection means is different from that when the transfer material is normally conveyed. A fixing device.

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