JP4337734B2 - Fixing apparatus and image forming apparatus - Google Patents

Description

  The present invention relates to a fixing device that heats and fixes a toner image on a recording sheet, and an image forming apparatus including the fixing device. More specifically, the present invention relates to a fixing device including a temperature sensor that detects the surface temperature of a roller to be tested in a non-contact manner and an image forming apparatus including the fixing device.

  An electrophotographic image forming apparatus includes a fixing device that fixes a toner image onto a recording sheet. As a fixing device, a roller system that includes a roller pair including a fixing roller and a pressure roller, and that fixes a toner image by passing a recording sheet through a nip portion of the roller pair is widely used. In this roller type fixing device, a heat source (halogen heater or the like) is provided in at least one of the roller pair, and the toner image is fixed on the recording paper by the heat and the pressure of the roller.

  In such a fixing process, temperature control of the roller is performed in order to perform stable fixing. Therefore, the fixing device is provided with several temperature sensors for measuring the surface temperature of the roller. As the temperature sensor, it is desirable to perform temperature detection without contact from the viewpoint of durability of the roller and the temperature sensor. As the non-contact temperature sensor, for example, a thermistor can be applied, and several fixing devices having a non-contact thermistor have been proposed (for example, Patent Document 1).

  Further, the above-described roller pair is provided such that at least one of the rollers can rotate around a predetermined fulcrum, and the rollers can be pressed and separated from each other. For example, in Patent Document 1, the pressure roller is provided so as to be rotatable about a predetermined support shaft. When the toner image is fixed, the pressure roller is in pressure contact with the fixing roller (pressure contact mode), and the pressure contact is released in the standby state (separation mode). In addition, there is a type in which the low pressure contact mode can be set for passing an envelope or cardboard.

Further, in order to detect the temperature of the roller with a non-contact temperature sensor with high accuracy, it is necessary to keep the distance between the temperature sensor and the roller to be detected constant. Therefore, in the fixing device disclosed in Patent Document 1, the temperature sensor is arranged at a position where the distance between the temperature sensor and the roller to be tested is the same in the pressure contact mode and the separation mode. Thereby, even if the test roller rotates, the distance between the temperature sensor and the test roller can be kept constant.
JP-A-6-274066

  However, the conventional fixing device has the following problems. That is, in order to detect the temperature of the roller with a non-contact temperature sensor (such as a non-contact thermistor) with high accuracy, in addition to keeping the distance between the temperature sensor and the test roller constant, the temperature sensor is tested. It is necessary to arrange it directly above the roller.

  FIG. 5 shows the relationship between the installation angle of the non-contact thermistor and the temperature detection accuracy. “Temperature detection accuracy” in this specification means the difference between the temperature measured by the radiation thermometer and the temperature calculated by the signal from the non-contact thermistor. The smaller the value, the higher the accuracy. . As shown in FIG. 5, it can be seen that the value of temperature detection accuracy increases as the angle from directly above the test roller, that is, the deviation from the vertical line including the test site increases. That is, it can be seen that there is a large difference between the temperature measured by the radiation thermometer and the temperature calculated by the signal from the non-contact thermistor. This is considered to be because heat rises mainly in the vertical direction.

  In the fixing device disclosed in Patent Document 1, the position of the temperature sensor is fixed. Therefore, even if it is possible to keep the distance between the roller and the temperature sensor constant, the temperature sensor cannot always be arranged directly above the roller to be tested. That is, at least one of the pair of rollers constituting the nip portion rotates around a predetermined fulcrum in order to correspond to the separation mode or the low pressure contact mode. For this reason, the temperature sensor cannot be kept immediately above the roller to be examined. Therefore, the detection accuracy varies.

  The present invention has been made to solve the problems of the conventional fixing device described above. That is, an object of the present invention is to provide a fixing device capable of performing temperature detection with a non-contact temperature sensor with high accuracy and an image forming apparatus including the same.

In order to solve this problem, a fixing device includes a fixing member having a heat source, and a roller that is rotatable about a predetermined fulcrum and that can be pressed against and separated from the fixing member. A fixing device that forms a nip portion by pressure contact between a fixing member and a roller, and fixes the image on the recording paper to the recording paper by passing the recording paper through the nip portion. A temperature acquisition means that acquires the surface temperature in a non-contact manner, engages with the rotation shaft of the roller via a bearing, and rotates about the rotation shaft of the roller according to the pressure contact and separation operation of the roller. And a holding member for holding. The image forming apparatus according to the present invention includes the fixing device according to the present invention.

  That is, the fixing device of the present invention includes a fixing member and a roller. As the fixing member, for example, a roller member incorporating a heater is applicable. The fixing member is not limited to a roller member, and may be an endless belt member. The roller is for constituting a fixing member and a nip portion. In the fixing device, the image on the recording paper is fixed on the recording paper by passing the recording paper through the nip portion. Examples of the recording paper include plain paper, cardboard, OHP sheet, envelope, and the like.

  Further, the roller is rotatable about a predetermined fulcrum and is provided so as to be capable of being pressed and separated from the fixing member. That is, the roller has a function as a pressure roller, and for example, presses against the fixing member in the pressure contact mode and operates so as to be separated from the fixing member in the separation mode.

  Furthermore, the fixing device of the present invention can acquire the roller surface temperature by the temperature acquisition means. This temperature acquisition means is a device that acquires the surface temperature of the roller in a non-contact manner (for example, a non-contact thermistor), and is disposed immediately above the roller. More specifically, the roller is disposed immediately above a portion to be examined (hereinafter referred to as “test portion”) of the roller, that is, above the vertical direction.

  In the fixing device of the present invention, the temperature acquisition means is held by the holding member. The holding member is engaged with the roller and moves in conjunction with the rotation of the roller. Further, the holding member is provided so as to be rotatable about the rotation axis of the roller. For example, the holding member is provided so as to be engaged with the rotation shaft of the roller via the bearing and to be rotatable about the rotation shaft. As a result, even when the roller rotates, the temperature acquisition member can continue to be positioned immediately above the roller by the rotation of the holding member itself. Further, since the roller rotates about the rotation axis of the roller, the distance between the temperature acquisition means and the roller is constant.

Further, the holding member may hold the temperature acquisition means directly above the roller and be urged downward in the vertical direction by the urging member or downward in the vertical direction by its own weight. In other words, the holding member is urged downward in the vertical direction, so that the position of the temperature acquisition means can be stably maintained immediately above the site to be tested even when the roller is rotated or externally shocked. . As the urging member, for example, a leaf spring attached to the frame of the fixing device is applicable. Further, when the center of gravity of the holding member is positioned below the center of the roller in the vertical direction, the same effect as that of the urging member can be obtained by the weight of the holding member.

  According to the present invention, the distance between the temperature acquisition means for temperature detection and the roller to be tested can be kept constant, and the temperature acquisition means can continue to be disposed immediately above the rollers. Therefore, a fixing device capable of performing temperature detection with a non-contact temperature sensor with high accuracy and an image forming apparatus including the same are provided.

  DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments embodying the present invention will be described below in detail with reference to the accompanying drawings. In this embodiment, the present invention is applied to a fixing device provided in an electrophotographic laser printer.

  The image forming apparatus 100 of this embodiment is an electrophotographic laser printer, and as shown in FIG. 1, a laser oscillator 2, a polygon mirror 3, and a reflecting mirror 4 are arranged as an optical system, A photosensitive drum 1, a charging charger 5, a developing device 6, a transfer charger 7, and a cleaning blade 8 are disposed. In addition, a paper feed roller 93, a paper discharge roller 94, a paper feed sensor 91, a paper discharge sensor 92, and a fixing device 10 are disposed as a paper transport unit. Note that FIG. 1 is for explaining the component configuration and operation procedure of the laser printer 100 and does not specify the arrangement of each device in the laser printer 100.

  Next, the operation of the laser printer 100 configured as described above will be briefly described. The photosensitive drum 1 rotates in the direction of the arrow in FIG. 1 and the surface is uniformly charged by the charging charger 5. Further, the laser light is modulated and emitted from the laser oscillator 2 based on the image signal. This laser beam is scanned in the main scanning direction by the polygon mirror 3, is reflected by the reflecting mirror 4, and enters the photosensitive drum 1. Thereby, an electrostatic latent image is formed on the photosensitive drum 1. This electrostatic latent image is developed by the developing device 6 to become a toner image. The toner image is transferred onto the recording paper S fed by the paper feed roller 93 by the transfer charger 7 disposed facing the photosensitive drum 1. Thereafter, the recording paper S to which the toner image has been transferred is heated by the fixing device 10, and the toner image is melted and fixed on the recording paper S by the heat. The recording paper S corresponds to plain paper, cardboard, OHP sheet, envelope, and the like. After the image is fixed, the recording paper S is discharged out of the apparatus by a paper discharge roller 94. With the above operation, printing for one sheet is performed.

  Next, the configuration of the fixing device 10 provided in the laser printer 100 of this embodiment will be described with reference to FIGS. 2 shows a schematic configuration in the pressure contact mode, and FIG. 3 shows a schematic configuration in the separation mode. FIG. 4 shows a side view seen from the direction of arrow A in FIG. The fixing device 10 is disposed in the laser printer 100 so that the bottom surface in FIGS. 2 to 4 is the lower side in the vertical direction.

  The fixing device 10 includes a fixing roller 11, a pressure roller 12, and a frame portion 13 that accommodates both rollers. The fixing roller 11 and the pressure roller 12 are in pressure contact to form a nip portion. Then, the recording sheet S on which the toner image is transferred is conveyed to the nip portion, and is fixed by passing through the nip portion.

  Further, the fixing roller 11 includes a first heater 11A having a high light distribution at both ends in the axial direction of the fixing roller 11 and a second heater 11B having a high light distribution at the center. The pressure roller 12 includes a heater 12A that uniformly heats the entire pressure roller 12. Further, the pressure roller 12 is provided so as to be rotatable around a fulcrum 191 installed in the frame portion 13. That is, in the fixing device 10, the pressure roller 12 rotates in the direction of arrow B in FIG. 2 according to the mode, so that the pressure contact with the fixing roller 11 (FIG. 2: pressure contact mode) and separation (FIG. 3: separation). Mode) is possible.

  Specifically, the fixing device 10 includes a pressure contact / separation mechanism using a cam 18 as shown in FIGS. That is, the pressure roller 12 is engaged with a pressure lever 19 that can be rotated around a fulcrum 191. Then, when the cam 18 presses the pressing portion 192 of the pressure lever 19, the pressure lever 19 rotates. Then, the pressure roller 12 rotates in conjunction with the rotation of the pressure lever 19, and the fixing roller 11 and the pressure roller 12 are separated. As a result, the fixing device 10 enters the separation mode.

  Further, the fixing device 10 includes a temperature sensor 14 that acquires the temperature of the surface portion of the pressure roller 12 and a holding member 15 that holds the temperature sensor 14. The temperature sensor 14 can detect the temperature in a non-contact manner with respect to the pressure roller 12 as a subject, and corresponds to, for example, a non-contact thermistor. The holding member 15 is engaged with the pressure roller 12 via a bearing 125, and is provided so as to be rotatable in the direction of arrow C in FIG. The interval between the temperature sensor 14 and the pressure roller 12 is constant because it can rotate around the rotation axis of the pressure roller 12. Further, the temperature sensor 14 is arranged so as to be directly above the test site of the pressure roller 12.

  In the fixing device 10, a leaf spring 16 having a rotatable roller 17 is attached to the frame portion 13. Further, the holding member 15 is urged downward in the vertical direction by the leaf spring 16. By constantly energizing the holding member 15 in this way, the temperature sensor 14 can be continuously arranged in the direction of energizing the pressure roller 12, that is, on the vertical line of the pressure roller 12. Specifically, when the pressure roller 12 rotates (arrow B in FIG. 2), the holding member rotates in the direction opposite to the rotation direction (arrow C in FIG. 2). The sensor 14 continues to be positioned immediately above the test site of the pressure roller 12.

  Note that the holding member 15 does not necessarily have to be biased by the leaf spring 16. That is, even if the leaf spring 16 is not provided, the temperature sensor 14 can be always disposed immediately above the pressure roller 12 by utilizing the weight of the holding member 15. For example, by adopting a configuration in which the center of gravity of the holding member 15 is positioned on the lower side in the vertical direction from the center of the pressure roller 12, the same effect as that of the urging member that urges downward in the vertical direction can be obtained. In this case, the configuration is simple and the number of parts is small as compared with the embodiment using the leaf spring 16.

  In the fixing device 10, the average value of the detected values obtained by the temperature sensor 14 within a predetermined time is used as an output value, and the surface temperature of the pressure roller 12 is calculated based on the output value. Then, the temperature control of the pressure roller 12 is performed using the calculated surface temperature.

  As described above in detail, in the fixing device 10 of this embodiment, the fixing roller 11 and the pressure roller 12 constitute a nip portion, and the pressure roller 12 is provided so as to be capable of being pressed against and separated from the fixing roller 11. It is said. Furthermore, the temperature sensor 14 that detects the surface temperature of the pressure roller 12 in a non-contact manner and the holding member 15 that holds the temperature sensor 14 are provided. The holding member 15 is provided so as to be rotatable about the rotation shaft of the pressure roller 12 and is urged downward by a leaf spring 16 in the vertical direction. By adopting such a structure, the distance between the temperature sensor 14 and the pressure roller 12 can be kept constant, and the temperature sensor 14 can always be disposed immediately above the pressure roller 12.

  And by always arrange | positioning the temperature sensor 14 directly on the pressure roller 12, as shown in FIG. 5, highly accurate temperature detection is attained. In the present embodiment, the term “directly above” does not mean that the pressure roller 12 is strictly located in the vertical direction of the test site, and the shift of the test site from the vertical line is within ± 5 degrees. If so, it can be said to be highly accurate. Therefore, a fixing device capable of performing temperature detection with a non-contact temperature sensor with high accuracy and an image forming apparatus including the same are realized.

  Note that this embodiment is merely an example, and does not limit the present invention. Therefore, the present invention can naturally be improved and modified in various ways without departing from the gist thereof. For example, in the fixing device of the present embodiment, the fixing member constituting the pressure roller and the nip portion is a fixing roller, but the invention is not limited to this. That is, as the fixing member, for example, an endless belt incorporating a heater may be used.

  In the embodiment, the present invention is applied to a laser printer, but the present invention is not limited to this. That is, even a copier, scanner, FAX, etc. can be applied as long as it has a fixing device. Further, it may be a color image forming apparatus or a monochrome image dedicated machine.

1 is a diagram illustrating a schematic configuration of a laser printer according to an embodiment. It is a figure which shows schematic structure (at the time of a press-contact mode) of the fixing device concerning embodiment. FIG. 3 is a diagram illustrating a schematic configuration of the fixing device according to the embodiment (in a separation mode). FIG. 3 is a diagram showing a schematic configuration of the fixing device shown in FIG. 2 as viewed from the direction of arrow A. It is a graph which shows the relationship between the installation angle of a thermistor, and detection accuracy.

Explanation of symbols

9 Control unit 10 Fixing device (fixing device)
11 Fixing roller (fixing member)
12 Pressure roller
13 Frame part 14 Temperature sensor (temperature acquisition means)
15 Holding member (holding member)
16 Leaf spring (biasing member)
18 Cam 19 Pressure lever 100 Laser printer (image forming apparatus)

Claims (6)

A fixing member having a heat source; and a roller that is rotatable about a predetermined fulcrum and that can be pressed against and separated from the fixing member. A nip portion is formed by pressing the fixing member and the roller. In the fixing device for fixing the image on the recording paper to the recording paper by passing the recording paper through the nip portion,
A temperature acquisition means that is located immediately above the roller and acquires the surface temperature of the roller in a non-contact manner;
A holding member that engages with the rotating shaft of the roller via a bearing, rotates around the rotating shaft of the roller in accordance with the pressing and separating operation of the roller, and holds the temperature acquisition means. A fixing device characterized. The fixing device according to claim 1,
A fixing device comprising a biasing member that biases the holding member downward in the vertical direction . The fixing device according to claim 1,
The fixing device is characterized in that the center of gravity of the holding member is positioned below the center of the roller in the vertical direction. A fixing member having a heat source; and a roller that is rotatable about a predetermined fulcrum and that can be pressed against and separated from the fixing member, and the fixing member and the roller constitute a nip portion. And an image forming apparatus including a fixing device that fixes the image on the recording paper by passing the recording paper through the nip portion.
A temperature acquisition means that is located immediately above the roller and acquires the surface temperature of the roller in a non-contact manner;
A holding member that engages with the rotating shaft of the roller via a bearing, rotates around the rotating shaft of the roller in accordance with the pressing and separating operation of the roller, and holds the temperature acquisition means. An image forming apparatus. The image forming apparatus according to claim 4,
An image forming apparatus comprising an urging member that urges the holding member downward in the vertical direction . The image forming apparatus according to claim 4,
The center of gravity of the holding member is located below the center of the roller in the vertical direction.

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