JP2004258151A - Fixing device and image forming apparatus with mounted fixing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fixing device capable of preventing a paper sheet from being soiled by a temperature sensor, extending the life of the sensor and realizing an accurate temperature detection. <P>SOLUTION: The fixing device 50 is provided with a fixing roller 51 to fix unfixed toner T on the paper P and a pressure roller 52 to form a nip through which the paper passes with the fixing roller 51 by coming into pressure contact with the fixing roller 51. The temperature sensor 54 brought into contact with the surface of the fixing roller 51 is arranged at the outside of a paper passing area L5. Also, a place where the temperature sensor 54 is arranged is positioned within the effective width L2 of the fixing roller 51, the effective heat generation width L3 of a halogen lamp 53 which is a heat source and the width L4 of the pressure roller 52. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a fixing device that inserts a sheet carrying an unfixed toner image into a nip between a fixing roller and a pressure roller, heats and melts the unfixed toner on the sheet, and fixes the unfixed toner on the sheet. Further, the present invention relates to an image forming apparatus equipped with the fixing device.
[0002]
[Prior art]
In an image forming apparatus such as a PPC (Plain Paper Copier), a facsimile, or a printer, at least one of a pair of rollers is heated by a built-in heat source, and an unfixed toner image is carried in a nip between the pair of rollers. A heat roller fixing method for fixing toner through paper is widely used. One example can be found in Patent Document 1.
[0003]
In the fixing device described in Patent Document 1, a halogen roller is arranged inside a pipe-shaped cored bar to form a fixing roller. A pressure roller having a core covered with an elastic layer is pressed against the fixing roller with a predetermined load. A thermistor is brought into contact with the surface of the fixing roller, and the amount of heat generated by the halogen lamp is controlled based on the surface temperature of the fixing roller detected by the thermistor.
[0004]
[Patent Document 1]
JP-A-8-220926
[Problems to be solved by the invention]
The fixing device described in Patent Document 1 has the following problem.
[0006]
The halogen lamp used as a heat source in the fixing device has a lamp coil disposed inside a straight glass tube, but no lamp coil is disposed at both ends of the tube. That is, both ends of the halogen lamp do not contribute to light emission. The portion excluding these end portions is the effective light emission width, that is, the effective heat generation width that can supply the fixing roller with the amount of heat required for fixing.
[0007]
In order to accurately detect the surface temperature of the fixing roller, the thermistor must be located within the effective heating width of the halogen lamp. By the way, in the case of the fixing device of Patent Document 1, the pressure roller does not cover the place where the thermistor is arranged. Since heat is not carried away by the pressure roller, heat is likely to accumulate at this location, which tends to cause excessive temperature rise. If the heat generation control of the halogen lamp is performed based on the detected temperature at this point, there may be a shortage of heat in the portion covered by the pressure roller, that is, the essential paper passing area.
[0008]
The present invention has been made in view of the above points, and an object of the present invention is to prevent a sheet from being contaminated by a temperature sensor in a fixing device having a fixing roller and a pressure roller, and to reduce the life of the temperature sensor. And to enable the temperature sensor to perform accurate temperature detection. Another object is to provide a high-performance image forming apparatus equipped with such a fixing device.
[0009]
[Means for Solving the Problems]
In order to achieve the above object, the fixing device according to the present invention is configured as follows. That is, in a fixing device in which a pressure roller is pressed against a fixing roller having a built-in heat source, a temperature sensor that contacts the surface of the fixing roller is outside the paper passing area, and the effective width of the fixing roller and the heat source. It is arranged at a position inside the effective heat generation width and the width of the pressure roller.
[0010]
100% of the unfixed toner on the paper is not fixed on the paper, but a small amount of the toner is partially transferred to the fixing roller. When the temperature sensor is in contact with the fixing roller in the paper passing area, the toner on the surface of the fixing roller gradually accumulates on the temperature sensor. When the accumulation amount increases, a problem of "image stain" occurs in which the toner mass separates from the temperature sensor and adheres to the sheet. In the case of the configuration of the present invention, since the temperature sensor is disposed outside the paper passing area, the toner does not adhere to the temperature sensor, and even if it adheres, the toner separated therefrom passes through the paper passing area. Since the paper is not stained, the problem of "image stain" does not occur.
[0011]
The surface of the fixing roller is smoothed by forming a film by coating or the like. However, the entire surface is not uniformly finished, and there are portions where the finish is inadequate at both ends. The width of the part excluding the unfinished part is called the "effective width". Since the temperature sensor is arranged inside the effective width, the temperature sensor contacts a smooth surface and has less wear. . That is, the service life of the temperature sensor can be extended.
[0012]
Further, since the location of the temperature sensor is inside the effective heat generation width of the heat source, the surface temperature of the location where the fixing operation is performed can be accurately measured.
[0013]
In addition, since the location of the temperature sensor is inside the width of the pressure roller, it is included in the effective heat generating portion of the heat source, but the heat of this portion is carried away by the pressure roller, causing an excessive rise in temperature. No Therefore, the temperature measured by the temperature sensor does not become higher than the actual temperature in the fixing work section, and the calorific value of the heat source and thus the surface temperature of the fixing roller can be appropriately controlled based on the measured value.
[0014]
Further, in the present invention, since the fixing device is mounted on the image forming apparatus, it is possible to obtain a print or a copy having high image quality without image contamination.
[0015]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an embodiment of the present invention will be described with reference to FIGS.
[0016]
FIG. 1 is a schematic sectional view showing a schematic structure of a tandem type color printer 1 which is an example of an image forming apparatus. FIG. 2 is a schematic sectional view showing a schematic structure of the image forming unit.
[0017]
In the printer 1, either full-color image output or monochrome image output is selected according to the color information of the document image data from the external computer. The image output speed is set to 20 sheets / minute in A4 size in both full color and monochrome. In this specification, specific numerical values such as dimensions, ratios, speeds, voltages, and temperatures appear in addition to the image output speed. However, these numerical values are examples of one preferred example and limit the scope of the invention. It does not do.
[0018]
A paper transport belt 8 is disposed inside the housing 2 of the printer 1. The paper transport belt 8 is wound around pulleys 10 and 11, and transports the paper horizontally from right to left in FIG. On the paper receiving side of the paper transport belt 8, a paper feed device 12 and a paper transport path 13 are arranged. A fixing device 50, a sheet conveyance path 15, and a discharge unit 16 are disposed on the sheet discharge side of the sheet conveyance belt 8. The discharge section 16 is provided on the upper surface of the housing 2.
[0019]
A total of four image forming units are arranged in series on the paper transport belt 8 from the upstream side to the downstream side in the paper transport direction. The four image forming units are, in order from the upstream side, a black image forming unit 30B, a yellow image forming unit 30Y, a cyan image forming unit 30C, and a magenta image forming unit 30M.
[0020]
FIG. 2 shows the structure of the image forming units 30B, 30Y, 30C, and 30M. Since the image forming units have the same structure, the identification symbols “B”, “Y”, “C”, and “M” are omitted, and only the reference numeral “30” is provided.
[0021]
The core of the image forming unit 30 is a photosensitive drum 4 using amorphous silicon as a photosensitive member, around which a main charger 5, an LED print head unit 6, a developing device 3, and a cleaning device 20 are arranged. I have. Also, as shown in FIG. 1, the transfer roller 9 faces the photosensitive drum 4 with the paper transport belt 8 interposed therebetween. The transfer roller 9 also has a role of supporting the sheet conveying belt 8 and bringing it into contact with the photosensitive drum 4. A voltage of -1.5 kV is applied to the transfer roller 9.
[0022]
The developing device 3 contains a developer in which toners of each color of black, yellow, cyan, and magenta and a ferrite carrier are mixed at a weight ratio of 5:95. The toner has a median diameter (by volume) of 9 μm as measured by a Coulter counter, and the ferrite carrier has an average particle diameter of 70 μm. The developing device 3 is provided with a developing sleeve 3a containing a fixed magnet (not shown).
[0023]
The photoreceptor drum 4 and the developing sleeve 3a face each other with a gap of 0.5 mm therebetween, and rotate so that the opposing surfaces move in the same direction. The peripheral speed of the photosensitive drum 4 is 100 mm / sec, and the peripheral speed of the developing sleeve 3a is 200 mm / sec. A magnetic brush is formed on the surface of the developing sleeve 3a by a developer. Further, the toner is positively charged by friction with the carrier. An uncut plate (not shown) is provided for the developing sleeve 3a. The gap between the cutting board and the developing sleeve 3a is 0.5 mm. A developing bias voltage of +300 V is applied to the developing sleeve 3a.
[0024]
The developer in the developing device 3 is consumed by the development. In order to supplement the consumed developer, toner supply containers 7B, 7Y, 7C, and 7M are provided corresponding to the image forming units 30B, 30Y, 30C, and 30M, and the developer is supplied by a conveying unit (not shown). As a result, the developing device 3 always holds an appropriate amount of the developer therein.
[0025]
The cleaning device 20 includes a rubber cleaning roller 21 that contacts the photosensitive drum 4, a cleaning blade 22 that scrapes toner not transferred onto the paper from the photosensitive drum 4, and a discharge spiral 23 that discharges the toner to a collection container (not shown). Having. The cover of the cleaning device 20 is not shown in FIG.
[0026]
The printer 1 performs an image output operation as follows.
[0027]
The surface of the photosensitive drum 4 is uniformly charged to +400 V by the main charger 5. When document image data is input from an external computer or the like, the LED print head 6 irradiates the surface of the photosensitive drum 4 with LED light corresponding to the document image data. On the surface of the photosensitive drum 4, the voltage of the exposed portion irradiated with the LED light is attenuated to +25 V, and an electrostatic latent image is formed together with the +400 V portion of the non-exposed portion. With the developing bias voltage of +300 V applied to the developing sleeve 3a, the positively charged toner in the developer adheres to the exposed portion, and the electrostatic latent image is visualized by the toner.
[0028]
The paper transport belt 8 carries the paper supplied from the paper feeding device 12 and travels in the same direction as the moving direction of the surface of the photosensitive drum 4 at the same peripheral speed of the photosensitive drum 4 at 100 mm / sec. The exposure timing of the photosensitive drum 4 by the LED print head 6 is set so that the transfer of the toner is started from a predetermined position on the sheet.
[0029]
When the paper on the paper transport belt 8 passes under the photosensitive drum 4, the toner attached to the photosensitive drum 4 is attracted to the paper by the voltage of -1.5 KV applied to the transfer roller 9. As a result, the toner is transferred to the paper.
[0030]
The toner not transferred to the paper is scraped off by the cleaning blade 22 and discharged to a collection container (not shown) by the discharge spiral 23. The cleaning roller 21 adjusts the surface of the photosensitive drum 4 after the toner transfer.
[0031]
The toner of each color of black, yellow, cyan, and magenta is sequentially transferred by the image forming units 30B, 30Y, 30C, and 30M, and the paper on which the color image is formed by the toner, which is not fixed, exits the paper transport belt 8 and is fixed. It is drawn into the device 50. Then, after the toner is fixed by the heat roller inside the fixing device 50, the toner is discharged to the discharge unit 16 via the paper conveyance path 15.
[0032]
Next, the structure of the fixing device 50 will be described with reference to FIGS. FIG. 3 is a schematic cross-sectional view illustrating a roller configuration of the fixing device 50, and FIG. 4 is a schematic front view illustrating a dimensional ratio of each part.
[0033]
The fixing device 50 includes a fixing roller 51 and a pressure roller 52. The fixing roller 51 and the pressure roller 52 are pressed against each other with a predetermined pressure to form a fixing nip having a predetermined width. The paper P carrying the unfixed toner T passes through the fixing nip.
[0034]
The fixing roller 51 is driven to rotate by a driving device (not shown). The pressure roller 52 rotates according to the fixing roller 51. The number of rotations of the fixing roller 51 is controlled such that the peripheral speed of the fixing roller 51 and the pressing roller 52 becomes 100 mm / sec, which is the same as the traveling speed of the sheet conveying belt 8.
[0035]
The fixing roller 51 forms a coating by covering an RFA (tetrafluoroethylene-per-fluoroalkylvinyl ether copolymer) or PTFE (polytetrafluoroethylene) tube on the surface of the metal core 53 of the metal pipe, or by coating. In addition, the smoothness and the releasability of the toner are improved. However, both ends are outside the area to be controlled in the film forming process, and the “effective width” is constituted by a portion excluding the both ends. The “effective width” varies depending on the individual fixing rollers 51. In FIG. 4, L1 is the width of the fixing roller 51, and L2 is its effective width.
[0036]
Inside the fixing roller 51, a halogen lamp 53 as a heat source is arranged. In FIG. 4, L3 is the effective emission width of the halogen lamp 53, that is, the effective heat generation width.
[0037]
The pressure roller 52 is formed by providing an elastic layer such as a silicone sponge on the outside of a cored bar and covering the surface thereof with an RFA or PTFE tube. In FIG. 4, L4 is the width of the pressure roller 52.
[0038]
Various types of paper P having different widths pass through a fixed paper passing area (a part of the width of the roller, through which the paper passes while contacting). In FIG. 4, L5 is the paper passing area of that width.
[0039]
A temperature sensor 54 contacts the surface of the fixing roller 51. The temperature sensor 54 is constituted by a thermistor.
[0040]
The dimensional ratio of each part is as follows. That is, the sheet passing area L5 is the smallest among L1 to L5. The temperature sensor 54 is arranged outside the paper passing area L5. The effective width L2 of the fixing roller 51, the effective heat generation width L3 of the halogen lamp 53, and the width L4 of the pressure roller 52 are all wider than the sheet passing area L5, and the location of the temperature sensor 54 is located inside the width. . The width L1 of the fixing roller 51 is wider than L2 to L5, and L2 to L5 are all included in L1.
[0041]
Since the temperature sensor 54 is disposed outside the paper passing area L5, toner does not adhere to the temperature sensor 54 via the fixing roller 51. Even if it adheres, the toner separated therefrom does not stain the sheet P passing through the sheet passing area L5, so that the problem of "image stain" does not occur.
[0042]
The temperature sensor 54 contacts the area of the effective width L2 of the fixing roller 51. Since this part is well-finished and has a smooth surface, the wear of the temperature sensor 54 is small.
[0043]
Since the location of the temperature sensor 54 is inside the effective heating width L3 of the halogen lamp 53, the surface temperature of the fixing roller 51 where the fixing operation is performed can be accurately measured. The measurement result is hardly influenced by the width of the sheet P.
[0044]
The location of the temperature sensor 54 is inside the width L4 of the pressure roller 52. Although this portion is an area in the effective heat generating portion of the halogen lamp 53, the heat of this portion is carried away by the pressure roller and does not cause an excessive temperature rise. Therefore, the temperature measured by the temperature sensor 54 does not become higher than the actual temperature in the fixing work section, and the calorific value of the halogen lamp 53 and, consequently, the surface temperature of the fixing roller 51 can be appropriately controlled based on this measured value. .
[0045]
Although the embodiments of the present invention have been described above, other various modifications can be made without departing from the gist of the present invention.
[0046]
【The invention's effect】
ADVANTAGE OF THE INVENTION According to this invention, image contamination by a temperature sensor is less likely to occur, the life of the temperature sensor is long, and the temperature sensor accurately measures the surface temperature of the place where the fixing operation is performed. A fixing device that does not cause a rise in temperature can be obtained. Further, it is possible to obtain an image forming apparatus in which image quality is improved by mounting such a fixing device.
[Brief description of the drawings]
FIG. 1 is a schematic cross-sectional view showing a schematic structure of a printer according to an embodiment of the present invention. FIG. 2 is a schematic cross-sectional view showing a schematic structure of an image forming section. FIG. 3 is a model showing a roller configuration of a fixing device. FIG. 4 is a schematic front view illustrating a dimensional ratio of each part of the fixing device.
REFERENCE SIGNS LIST 1 Printer 2 Housing 12 Paper feeder 13, 15 Paper transport path 16 Discharge unit 30B, 30Y, 30C, 30M Image forming unit 3 Developing units 7B, 7Y, 7C, 7M Toner supply container 50 Fixing unit 51 Fixing roller 52 Pressure roller 53 Halogen lamp 54 Temperature sensor L1 Width of fixing roller L2 Effective width of fixing roller L3 Effective heat generation width of halogen lamp L4 Width of pressure roller L5 Paper passing area

Claims (2)

In a fixing device in which a pressure roller is pressed against a fixing roller having a built-in heat source,
A temperature sensor that contacts the surface of the fixing roller is disposed at a position outside the paper passing area and inside the effective width of the fixing roller, the effective heat generation width of the heat source, and the width of the pressure roller. A fixing device. An image forming apparatus comprising the fixing device according to claim 1.

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