JP5704775B2 - Fixing apparatus and image forming apparatus having the same - Google Patents

Description

  The present invention relates to a fixing device for fixing an unfixed toner image mounted in an image forming apparatus such as a copying machine or a printer, and more particularly to a mechanism for detecting rotation of a fixing roller.

  In an electrophotographic image forming apparatus, at least one roller (fixing roller) of a pair of rollers forming a nip is heated, and a sheet carrying an unfixed toner image is inserted into the nip of the pair of rollers on a recording medium. A heat roller fixing method for fixing toner is widely used.

  Also, as a heat roller fixing method, an endless fixing belt is bridged between the fixing roller and the heating roller, the fixing belt is heated by the heat source of the heating roller, and the nip between the fixing roller and the pressure roller is passed through the fixing belt. A belt heating method for fixing an unfixed toner image on a recording medium is also used.

  As a heating method for such a fixing roller and a heating roller (heat roller), a lamp method in which heating is performed by a lamp such as a halogen lamp incorporated in the roller is known. In response, an induction heating (IH: Induction Heating) system has been proposed in which an alternating magnetic field is linked to a magnetic conductor to generate eddy currents.

  In the IH method, since the induction heating unit including the exciting coil and the core is large, the induction heating unit is often disposed outside the fixing roller or the heating roller, and the roller is often heated from the outside. In this case, if heating is started in a state where the roller is not rotating, only a part of the roller surface is heated. In addition, a temperature detection sensor that detects the surface temperature of the roller is arranged, but if the placement position of the induction heating unit and the temperature detection sensor differs in the circumferential direction of the roller, abnormal temperature rise cannot be detected, and the roller is deformed by heat. May cause smoke, fire. Therefore, it is common to pass an electric current through an induction heating part in the state where the roller is rotating.

  For example, in Patent Documents 1 and 2, the rotation detecting means including an optical sensor (photo sensor) and an actuator is used to detect the presence or absence of rotation of the heating roller, and the current flowing through the induction heating unit is determined based on the detection result. An IH type fixing device controlled is disclosed.

JP 2002-82549 A JP-A-2005-70321

  In the methods of Patent Documents 1 and 2, the actuator rotates in conjunction with the rotation driving of the fixing roller and the heating roller, and the presence or absence of rotation of the heating roller is detected by opening or blocking the optical path of the detection unit of the optical sensor. ing. Specifically, the rotation of the fixing roller is recognized when the switching portion (edge) of the light reception signal level of the detection unit is detected a plurality of times (for example, twice or more in 300 msec) within a predetermined time.

  However, when there is a gear meshing failure in the driving mechanism of the fixing roller or the heating roller, so-called tooth skipping, in which one gear tooth slips over the other gear tooth, is likely to occur. As a result, the gear rotates slightly when the gear is engaged, and if a tooth jump occurs, the gear rotates slightly reversely due to the rotational load, so the actuator connected to the gear swings in small increments and the detection unit of the optical sensor May be opened or blocked. For this reason, there is a problem in that it is erroneously detected that the fixing roller and the heating roller are rotating although they are not rotating.

  SUMMARY OF THE INVENTION In view of the above problems, the present invention provides a fixing device having a rotation detection mechanism that can accurately detect rotation of a roller even if tooth skipping occurs due to poor gear meshing, and an image forming apparatus including the same. Objective.

  In order to achieve the above object, a first configuration of the present invention includes a heated rotating body heated by a heating unit, a drive input gear for inputting a driving force to the heated rotating body, and a rotation detection mechanism. It is a fixing device. The rotation detection mechanism includes an output side gear fixed to a heated rotating body, an actuator gear having a plurality of light shielding plates formed at equal intervals on the outer peripheral surface that is rotated by the driving force of the output side gear, and the light shielding of the actuator gear. An optical sensor that detects opening or blocking of an optical path by a plate, and a gear train including a plurality of idle gears having one end connected to the output gear and the other end connected to an actuator gear. It detects whether or not the rotating body is rotating. The optical sensor includes a first sensor and a second sensor that are arranged at intervals different from the interval between the light shielding plates. The second sensor is arranged on the upstream side of the first sensor with respect to the rotation direction of the actuator gear so that the distance from the first sensor is larger than the distance between the light shielding plates. The rotation detection mechanism includes a first pattern in which the optical path of the first sensor and the second sensor are both blocked, a second pattern in which only the optical path of the second sensor is opened, Of the third pattern in which the optical paths of the sensor and the second sensor are both opened, and the fourth pattern in which only the optical path of the first sensor is opened, the first pattern and the second pattern, the second pattern and the third pattern, When any combination of the third pattern and the fourth pattern, or the fourth pattern and the first pattern is repeatedly detected in a plurality of times in the order, it is determined that the heated rotating body is not normally rotated.

  According to a second aspect of the present invention, in the fixing device having the above-described structure, the heating unit is an induction heating unit that heats the rotating body to be heated from the outside by electromagnetic induction.

  A third configuration of the present invention is an image forming apparatus including the fixing device having the above configuration.

  According to the first configuration of the present invention, the second sensor is arranged on the upstream side of the first sensor with respect to the rotation direction of the actuator gear so that the distance from the first sensor is larger than the distance between the light shielding plates. In this case, the first sensor and the second sensor may be any combination of the first pattern and the second pattern, the second pattern and the third pattern, the third pattern and the fourth pattern, and the fourth pattern and the first pattern. Since the rotation of the heated rotating body is judged to be not normal when it is detected repeatedly several times in order, the actuator gear repeats forward and reverse rotation in small increments due to tooth skipping of the drive input gear, and the light path by the light shielding plate When opening or shutting off of the rotating body is detected, it is possible to reliably detect the rotation abnormality of the heated rotating body.

  Further, according to the second configuration of the present invention, in the fixing device of the first configuration, by using an induction heating unit that heats the heated rotating body from the outside by electromagnetic induction as the heating unit, the warm-up time can be reduced. The detection accuracy of the rotation of the heated rotating body can be improved while shortening and saving energy.

  In addition, according to the third configuration of the present invention, by mounting the fixing device having the first or second configuration, thermal deformation of the rotating body caused by heating while the rotating body to be heated is stopped, There is no fear of smoke or fire, and the image forming apparatus is excellent in safety.

1 is a schematic cross-sectional view showing an internal configuration of an image forming apparatus equipped with a fixing device of the present invention. Enlarged view of the vicinity of the fixing device 13 in FIG. 1 is a perspective view of a fixing device 13 according to an embodiment of the present invention. Side view of the fixing device 13 as viewed from the right side of FIG. A flowchart showing rotation detection and heating control procedures of the fixing roller 131 in the fixing device 13 of the present invention. Schematic side view showing how the rotation of the fixing roller 131 is detected by the rotation detection mechanism 60 The partial enlarged view which shows the state by which the optical path of the detection part 50a of the 1st sensor 41a and the detection part 50b of the 2nd sensor 41b is interrupted | blocked by the light shielding plates 42a and 42b, respectively. The partial enlarged view which shows the state by which the optical path of the detection part 50a of the 1st sensor 41a is open | released and the optical path of the detection part 50b of the 2nd sensor 41b is interrupted | blocked The elements on larger scale which show the state where the optical path of the detection part 50a of the 1st sensor 41a and the detection part 50b of the 2nd sensor 41b is open | released together. The partial enlarged view which shows the state by which the optical path of the detection part 50a of the 1st sensor 41a is interrupted | blocked, and the optical path of the detection part 50b of the 2nd sensor 41b is open | released Schematic side view showing the operation of the rotation detection mechanism 60 when tooth skipping occurs between the drive input gear 30 and the roller drive gear 31 of the fixing roller 131.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic cross-sectional view of an image forming apparatus equipped with a fixing device of the present invention. Here, a tandem type color image forming apparatus is shown. In the main body of the color printer 100, four image forming portions Pa, Pb, Pc, and Pd are sequentially arranged from the upstream side in the transport direction (left side in FIG. 1). These image forming portions Pa to Pd are provided corresponding to images of four different colors (cyan, magenta, yellow, and black), and cyan, magenta, and yellow are respectively performed by charging, exposure, development, and transfer processes. And a black image are sequentially formed.

  These image forming portions Pa to Pd are provided with photosensitive drums 1a, 1b, 1c and 1d which carry visible images (toner images) of the respective colors, and are further illustrated by a driving means (not shown). 1, an intermediate transfer belt 8 that rotates counterclockwise is provided adjacent to each of the image forming portions Pa to Pd. The toner images formed on the photosensitive drums 1a to 1d are sequentially primary-transferred and superimposed on the intermediate transfer belt 8 that moves while contacting the photosensitive drums 1a to 1d, and then the secondary transfer roller. 9 is secondarily transferred onto a sheet P as an example of a recording medium. Further, after being fixed on the sheet P in the fixing device 13, the sheet is discharged from the apparatus main body. An image forming process for each of the photosensitive drums 1a to 1d is executed while rotating the photosensitive drums 1a to 1d clockwise in FIG.

  The paper P on which the toner image is transferred is accommodated in a paper cassette 16 at the lower part of the apparatus, and is driven by a secondary transfer roller 9 and a driving roller for an intermediate transfer belt 8 described later via a paper feed roller 12a and a registration roller pair 12b. 11 to the nip portion. A sheet made of dielectric resin is used for the intermediate transfer belt 8, and a (seamless) belt having no seam is mainly used. Further, a blade-like belt cleaner 19 for removing toner remaining on the surface of the intermediate transfer belt 8 is disposed on the downstream side of the secondary transfer roller 9.

  Next, the image forming units Pa to Pd will be described. There are chargers 2a, 2b, 2c, and 2d for charging the photosensitive drums 1a to 1d and image information on the photosensitive drums 1a to 1d around and below the photosensitive drums 1a to 1d that are rotatably arranged. The exposure device 5 for exposing the toner, the developing devices 3a, 3b, 3c and 3d for forming toner images on the photosensitive drums 1a to 1d, and the developer (toner) remaining on the photosensitive drums 1a to 1d are removed. Cleaning parts 7a, 7b, 7c and 7d are provided.

  When image data is input from a host device such as a personal computer, first, the surfaces of the photosensitive drums 1a to 1d are uniformly charged by the chargers 2a to 2d, and then light is irradiated according to the image data by the exposure device 5. The electrostatic latent images corresponding to the image data are formed on the respective photosensitive drums 1a to 1d. Each of the developing devices 3a to 3d is filled with a predetermined amount of a two-component developer containing toner of each color of cyan, magenta, yellow, and black. In addition, when the ratio of the toner in the two-component developer filled in each developing device 3a to 3d falls below a specified value due to the formation of a toner image described later, each developing device 3a to 3d is transferred from the toner container 4a to 4d. Toner is replenished. The toner in the developer is supplied onto the photosensitive drums 1a to 1d by the developing devices 3a to 3d and electrostatically adheres to the electrostatic latent image formed by the exposure from the exposure device 5. A toner image is formed.

  Then, by applying a predetermined transfer voltage to the primary transfer rollers 6 a to 6 d, cyan, magenta, yellow, and black toner images on the photosensitive drums 1 a to 1 d are primarily transferred onto the intermediate transfer belt 8. These four color images are formed with a predetermined positional relationship predetermined for forming a predetermined full-color image. Thereafter, the toner remaining on the surfaces of the photosensitive drums 1a to 1d is removed by the cleaning units 7a to 7d in preparation for the subsequent formation of a new electrostatic latent image.

  The intermediate transfer belt 8 is stretched between an upstream tension roller 10 and a downstream drive roller 11, and the intermediate transfer belt 8 is counterclockwise as the drive roller 11 is rotated by a drive motor (not shown). When rotation starts around, the paper P is conveyed from the registration roller 12b to the nip portion (secondary transfer nip portion) between the driving roller 11 and the secondary transfer roller 9 provided adjacent thereto at a predetermined timing. The full color image on the intermediate transfer belt 8 is transferred onto the paper P. The paper P on which the toner image has been transferred passes through the paper transport path 18 and is transported to the fixing device 13.

  The paper P conveyed to the fixing device 13 is heated and pressurized by the fixing roller pair 13a, and the toner image is fixed on the surface of the paper P, thereby forming a predetermined full color image. The paper P on which the full-color image is formed is distributed in the transport direction by the branching section 14 that branches in a plurality of directions. When an image is formed only on one side of the paper P, it is discharged as it is onto the discharge tray 17 by the discharge roller 15.

  On the other hand, when images are formed on both sides of the paper P, the paper P that has passed through the fixing device 13 is once transported in the direction of the discharge roller 15, and the discharge roller 15 is reversed after the trailing edge of the paper P has passed the branch portion 14. By rotating and switching the conveyance direction of the branching portion 14, the paper P is distributed from the rear end of the paper P to the reverse conveyance path 20, and is re-conveyed to the secondary transfer nip portion with the image surface reversed. Then, after the next image formed on the intermediate transfer belt 8 is transferred to the surface of the paper P where the image is not formed by the secondary transfer roller 9 and conveyed to the fixing device 13 to fix the toner image, It is discharged to the discharge tray 17.

  FIG. 2 is an enlarged view of the vicinity of the fixing device 13 in FIG. Portions common to FIG. 1 are denoted by the same reference numerals and description thereof is omitted. As shown in FIG. 2, the fixing device 13 is an IH type using an electromagnetic induction heating type heat source, and is disposed adjacent to the fixing roller 131 and a fixing roller pair 13 a including a fixing roller 131 and a pressure roller 132. An induction heating unit 133 is provided, and a temperature sensor 134 formed of a thermistor or the like that detects the temperature of the surface of the fixing roller 131 is provided. The induction heating unit 133 and the temperature sensor 134 are fixed to the image forming apparatus 100 main body, and the fixing roller 131 and the pressure roller 132 are rotatably held by the image forming apparatus 100 main body.

  The fixing roller 131 includes a base material made of cylindrical stainless steel, and an elastic layer made of a silicone rubber sponge for improving elasticity and releasability to the nip portion N in pressure contact with the pressure roller 132. Between the layers, a heat insulating layer and an induction heating layer are provided in this order from the substrate side.

  The pressure roller 132 melts an unfixed toner image at the nip portion N, a base material made of cylindrical stainless steel, an elastic layer made of silicone rubber formed on the base material to impart elasticity to the nip portion N, and the like. In order to improve releasability at the time of fixing, a release layer comprising a fluororesin tube covering the surface of the elastic layer is provided.

  The pressure roller 132 is driven to rotate by a drive source (not shown) such as a motor, and further pressurizes the fixing roller 131 in the center direction. As a result, when the pressure roller 132 comes into pressure contact with the fixing roller 131 and the pressure roller 132 rotates, the fixing roller 131 is driven to rotate in the reverse direction with respect to the pressure roller 132.

  The temperature sensor 134 has an axial direction (width direction) on the surface of the fixing roller 131 and an axial direction that becomes a non-sheet passing area when a narrow width sheet such as B5 or A4 is passed. It arrange | positions so that it may oppose both ends, and the temperature of each area | region is detected. Based on the temperature detected by the temperature sensor 134, the power source of the induction heating unit 133 is controlled, and the surface of the fixing roller 131 is held at a predetermined temperature.

  The induction heating unit 133 includes an exciting coil 133a and a core 133b, and heats the fixing roller 131 by electromagnetic induction. An exciting coil 133a made of copper wire is wound around a hobbin (not shown), and is arranged to face a part of the outer peripheral surface of the fixing roller 131 so as to circulate around the central portion of the core 133b in the axial direction. Yes. The exciting coil 133a is connected to a high voltage power source (not shown), and generates a magnetic flux by a high frequency current supplied from the high voltage power source. A magnetic flux generated from the induction heating unit 133 is generated in a direction parallel to the paper surface of FIG. 2 and penetrates the induction heating layer of the fixing roller 131. An eddy current is generated around the magnetic flux of the induction heating layer, and when the eddy current flows, Joule heat is generated by the electrical resistance in the induction heating layer, and the induction heating layer generates heat.

  The power of the power source is controlled based on the temperature detected by the temperature sensor 134 so that the fixing roller 131 reaches a predetermined temperature by the induction heating unit 133. When the fixing roller 131 is heated and heated to a predetermined temperature, the paper P sandwiched by the nip portion N is heated and pressed by the pressure roller 132, whereby the powder on the paper P is heated. The toner in the state is melted and fixed.

  3 is a perspective view of the fixing device 13, and FIG. 4 is a side view of the fixing device 13 as viewed from the right in FIG. For convenience of explanation, FIGS. 3 and 4 mainly show the fixing roller 131, the pressure roller 132, the driving mechanism of each roller, and the rotation detection mechanism. The induction heating unit 133, the temperature sensor 134, and the like are shown in FIG. Description is omitted.

  As shown in FIG. 3, when the drive input gear 30 to which the drive force of a drive motor (not shown) is input rotates, the roller drive gear 31 that meshes with the drive input gear 30 rotates and the pressure roller 132 rotates. . Then, the fixing roller 131 to which the pressure roller 132 is pressed is rotated following the pressure roller 132.

  On the side where the drive input gear 30 and the roller drive gear 31 are not provided (the right side in FIG. 3), a large-diameter gear 35 fixed to one end of the rotation shaft of the fixing roller 131 and a first gear meshing with the large-diameter gear 35. An idle gear 37, a second idle gear 39 that meshes with the first idle gear 37, and an actuator gear 40 that meshes with the second idle gear 39 are arranged. A first sensor 41 a and a second sensor 41 b are disposed facing the actuator gear 40. The first idle gear 37, the second idle gear 39, the actuator gear 40, the first sensor 41a, and the second sensor 41b constitute a rotation detection mechanism 60 (see FIG. 5) of the fixing roller 131.

  On the outer peripheral surface of the actuator gear 40, a plurality of (eight in this case) light shielding plates 42 for switching ON and OFF of the first sensor 41a and the second sensor 41b are fixed at equal intervals.

  The pressure roller 132 is supported by an arm member 43 that rotates about a fulcrum 43 a. The arm member 43 is urged toward the fixing roller 131 by the urging force of the pressing spring 45. As a result, the pressure roller 132 is pressed against the fixing roller 131 with a predetermined pressure.

  The first sensor 41 a and the second sensor 41 b are PI (photo interrupter) sensors in which a detection unit including a light emitting unit and a light receiving unit is provided on the opposed inner surfaces of the U-shape in plan view, and the outer peripheral surface of the actuator gear 40. The light shielding plates 42 are arranged at intervals shorter than the intervals (pitch) of the light shielding plates 42 by a predetermined distance.

  When the light shielding plate 42 blocks the optical path of the detection unit of the first sensor 41a and the second sensor 41b, the light reception signal level of the detection unit is switched from HIGH to LOW. The rotation of the fixing roller 131 can be detected based on the detection timing of the first sensor 41a and the second sensor 41b. When rotation of the fixing roller 131 is detected, a detection signal is transmitted to a control unit (not shown), and a control signal is transmitted from the control unit to the induction heating unit 133 (see FIG. 2) to heat the fixing roller 131. Is started.

  FIG. 5 is a flowchart showing the rotation detection procedure of the fixing roller 131 in the fixing device 13 of the present invention. The operation of the rotation detection mechanism 60 used in the fixing device 13 of the present invention will be described in detail along the steps of FIG. First, when a printing command is input by the user (step S1), the pressure roller 132 is rotationally driven based on a drive signal from the control unit, and the fixing roller 131 pressed against the pressure roller 132 also starts to rotate. (Step S2). Then, it is detected by the rotation detection mechanism 60 whether or not the fixing roller 131 is rotating normally (step S3).

  FIG. 6 is a schematic side view showing a state in which the rotation of the fixing roller 131 is detected by the rotation detection mechanism 60. When the pressure roller 132 is rotationally driven by the driving force from the drive input gear 30 and the fixing roller 131 starts to rotate following the pressure roller 132, the large-diameter gear 35 fixed to the rotation shaft of the fixing roller 131 is also generated. It rotates in the same direction as the fixing roller 131 (counterclockwise in FIG. 6).

  Next, the first idle gear 37 that meshes with the large-diameter gear 35 rotates in the clockwise direction, and the second idle gear 39 that meshes with the first idle gear 37 rotates in the counterclockwise direction in FIG. The actuator gear 40 meshing with the gear rotates in the clockwise direction of FIG.

  Since the light shielding plate 42 sequentially passes through the detection units of the first sensor 41a and the second sensor 41b by the rotation of the actuator gear 40, detection signals are transmitted from the first sensor 41a and the second sensor 41b to the control unit and fixed. The rotation of the roller 131 is detected. At this time, the detection patterns by the first sensor 41a and the second sensor 41b are as shown in Table 1.

  In Table 1, flag “0” indicates a state in which the optical path of the detection unit of the sensor is opened, and flag “1” indicates a state in which the optical path of the detection unit of the sensor is shielded. For example, in the case of pattern A, as shown in FIG. 7, the optical path of the detection unit 50a of the first sensor 41a and the optical path of the detection unit 50b of the second sensor 41b are blocked by the light shielding plates 42a and 42b, respectively. Show.

  When the actuator gear 40 rotates by a predetermined amount from the state of FIG. 7, the detection unit 50a of the first sensor 41a enters between the light shielding plates 42a and 42b and the optical path is opened as shown in FIG. The optical path of the detection unit 50b is in a pattern B state blocked by the light shielding plate 42b.

  When the actuator gear 40 is rotated by a predetermined amount from the state of FIG. 8, the detection unit 50a of the first sensor 41a enters between the light shielding plates 42a and 42b, and the detection unit 50b of the second sensor 41b is rotated as shown in FIG. By entering between the light shielding plates 42b and 42c, the state of the pattern C in which the optical paths of the detection unit 50a and the detection unit 50b are both opened is obtained.

  When the actuator gear 40 rotates by a predetermined amount from the state of FIG. 9, as shown in FIG. 10, the optical path of the detection unit 50a of the first sensor 41a is blocked by the light blocking plate 42b, and the detection unit 50b of the second sensor 41b is blocked by light. The pattern D enters between the plates 42b and 42c and the optical path is open. When the actuator gear 40 rotates by a predetermined amount from the pattern D, the optical path of the detection unit 50a of the first sensor 41a and the optical path of the detection unit 50b of the second sensor 41b are shielded by the light shielding plates 42b and 42c, respectively. Return to Pattern A.

  That is, when the fixing roller 131 is rotating normally, the first sensor 41a and the second sensor 41b repeatedly detect the patterns A to D in the order of A → B → C → D shown in Table 1. Therefore, when two or more detection patterns among the patterns A to D are detected within the predetermined time (for example, 300 msec) in the above order, it is determined that the fixing roller 131 is rotating normally.

  Returning to FIG. 5, it is determined whether or not two or more of the patterns A to D described above are detected by the first sensor 41a and the second sensor 41b in a predetermined order in the control unit (step S4). If it is determined that the fixing roller 131 is rotated, electric power is supplied to the induction heating unit 133 to start heating the fixing roller 131 (step S5).

  Then, power is continuously supplied until the surface of the fixing roller 131 reaches a predetermined fixing temperature, and when the temperature sensor 134 determines that the fixing temperature has been reached (YES in step S6), at a predetermined timing. The toner image formation in the image forming portions Pa to Pd and the paper supply from the paper cassette 16 are started, and printing is executed (step S7).

  On the other hand, if it is determined in step S4 that the fixing roller 131 is not rotating normally (NO in step S4), heating of the fixing roller 131 is not started and the liquid crystal display unit (not shown) of the operation panel is started. A warning message is displayed (step S8), and the printing operation is stopped.

  FIG. 11 is a schematic side view showing the operation of the rotation detection mechanism 60 when tooth skipping occurs between the drive input gear 30 and the roller drive gear 31 (see FIG. 3 for both). In this case, the roller drive gear 31 repeats a slight rotation (forward rotation) when meshing with the drive input gear 30 and a slight reverse rotation due to the rotational load when the tooth skip occurs, so The fixing roller 131 that rotates following the pressure roller 132 repeats forward and reverse rotations in small increments.

  As a result, the large-diameter gear 35 fixed to the fixing roller 131 and the first gear member 37a of the first idle gear 37 meshing with the large-diameter gear 35 also repeat the clockwise and counterclockwise rotations in small increments. At this time, depending on the rotational position of the actuator gear 40, the light shielding plate 42 blocks or opens the optical path of the detection unit 50a of the first sensor 41a or the detection unit 50b of the second sensor 41b. Alternatively, the edge is detected by the second sensor 41b.

  At this time, for example, when the actuator gear 40 reciprocates between the state of FIG. 7 and the state of FIG. 8, only the pattern A and the pattern B are repeatedly detected. Similarly, when reciprocating between the state of FIG. 8 and the state of FIG. 9, only the pattern B and the pattern C are repeatedly detected. Further, when reciprocating between the state of FIG. 9 and the state of FIG. 10, only the pattern C and the pattern D are repeatedly detected, and when reciprocating between the state of FIG. 10 and the state of FIG. 7, only the pattern D and the pattern A are repeatedly detected. Is done. Therefore, the detection patterns of the first sensor 41a and the second sensor 41b are not repeated in the order of A → B → C → D shown in Table 1, and erroneously detected that the fixing roller 131 is rotating normally. There is no.

  Moreover, although the said embodiment demonstrated the case where the 1st sensor 41a and the 2nd sensor 41b were arrange | positioned by the space | interval shorter by the predetermined distance than the space | interval (pitch) of the light shielding plate 42, the 1st sensor 41a and the 2nd sensor were demonstrated. 41b can also be arranged at intervals longer than the interval (pitch) of the light shielding plates 42 by a predetermined distance. In this case, the detection patterns by the first sensor 41a and the second sensor 41b are as shown in Table 2.

  When the actuator gear 40 rotates by a predetermined amount after the pattern A in which the optical path of the detection unit 50a of the first sensor 41a and the optical path of the detection unit 50b of the second sensor 41b are both blocked by the light shielding plates 42a and 42b is detected. Since the optical path of the second sensor 41b arranged upstream in the rotation direction is opened first, the pattern D in which the first sensor 41a is “1” and the second sensor 41b is “0” is detected.

  When the actuator gear 40 rotates by a predetermined amount after the pattern D is detected, the optical path of the first sensor 41a disposed on the downstream side in the rotation direction is also opened, so that both the first sensor 41a and the second sensor 41b are “0”. When the pattern C is detected and the actuator gear 40 further rotates by a predetermined amount, the optical path of the second sensor 41b disposed upstream in the rotation direction is blocked first, so that the first sensor 41a is “0”. The pattern B in which the second sensor 41b is “1” is detected.

  That is, when the fixing roller 131 is rotating normally, the first sensor 41 a and the second sensor 41 b repeatedly detect the patterns A to D in the order of A → D → C → B shown in Table 2. Therefore, when two or more detection patterns among the patterns A to D are detected within the predetermined time (for example, 300 msec) in the above order, it is determined that the fixing roller 131 is rotating normally.

  As described above, according to the configuration of the present invention, it is determined that the fixing roller 131 is normally rotated when the first sensor 41a and the second sensor 41b detect predetermined detection patterns in a certain order. Accordingly, it is possible to reliably prevent erroneous detection of the rotation of the fixing roller 131 when tooth skipping of the drive input gear 30 occurs. Accordingly, the fixing device 13 and the image forming apparatus 100 are excellent in safety because there is no risk of thermal deformation, smoke generation, or ignition of the roller due to heating with the fixing roller 131 stopped.

  Here, the large-diameter gear 35 fixed to the fixing roller 131 and the actuator gear 40 are connected using the first idle gear 37 and the second idle gear, but three or more idle gears are used. May be connected.

  In addition, this invention is not limited to the said embodiment, A various change is possible in the range which does not deviate from the meaning of this invention. For example, in the above-described embodiment, the IH type fixing device 13 having the induction heating unit 133 has been described as an example, but the present invention can be applied to a fixing device in which the fixing roller is heated by another heating method. Of course.

  For example, an endless fixing belt is bridged between a fixing roller and a heating roller, the heating roller is heated from the outside to heat the fixing belt, and an unfixed toner image is formed at the nip between the fixing roller and the pressure roller via the fixing belt. In the case of a belt heating method for fixing the toner image to the recording medium, it can be used as a rotation detection mechanism for the heating roller.

  The present invention is not limited to the tandem type color printer 100 as shown in FIG. 1, but can be applied to various image forming apparatuses including a fixing device such as a monochrome copying machine, a digital multi-function peripheral, a facsimile machine, and a laser printer. is there.

  The present invention can be applied to a fixing device that includes a heating unit that heats a heated rotating body such as a fixing roller from the outside and needs to be heated while the heated rotating body is rotating. Use of the present invention can prevent erroneous detection of rotation of the heated rotating body and reliably prevent thermal deformation, smoke generation, and ignition due to overheating of the heated rotating body when tooth skipping occurs due to poor gear meshing. It becomes a highly secure fixing device.

Pa to Pd Image forming unit 13 Fixing device 13a Fixing roller pair 131 Fixing roller (heated rotating body)
132 Pressure roller 133 Induction heating unit (heating means)
30 Drive input gear 31 Roller drive gear 35 Large diameter gear (output side gear)
37 first idle gear 39 second idle gear 40 actuator gear 41a first sensor (optical sensor)
41b Second sensor (optical sensor)
42, 42a-42c Light-shielding plates 50a, 50b Detection unit 60 Rotation detection mechanism 100 Color printer

Claims (3)

A heated rotating body heated by a heating means;
A drive input gear for inputting a driving force to the heated rotating body;
An output side gear fixed to the heated rotating body, an actuator gear having a plurality of light shielding plates formed at equal intervals on an outer peripheral surface rotated by a driving force of the output side gear, and a light shielding plate of the actuator gear An optical sensor for detecting opening or closing of an optical path, and a gear train including a plurality of idle gears having one end connected to the output side gear and the other end connected to the actuator gear. A rotation detection mechanism that detects whether or not the rotating body is rotating;
In a fixing device having
The optical sensor is composed of a first sensor and a second sensor arranged at intervals different from the interval between the light shielding plates,
The second sensor is arranged on the upstream side of the first sensor with respect to the rotation direction of the actuator gear so that a distance from the first sensor is larger than a distance between the light shielding plates,
In the rotation detection mechanism, the first sensor and the second sensor have a first pattern in which both of the optical paths of the first sensor and the second sensor are blocked, and only an optical path of the second sensor is opened. Of the two patterns, the third pattern in which the optical paths of the first sensor and the second sensor are both open, and the fourth pattern in which only the optical path of the first sensor is open, the first pattern and the second pattern When a combination of any one of the pattern, the second pattern and the third pattern, the third pattern and the fourth pattern, and the fourth pattern and the first pattern is repeatedly detected in the order. It is determined that the heated rotating body is not normally rotated.   The fixing device according to claim 1, wherein the heating unit is an induction heating unit that heats a rotating body to be heated from the outside by electromagnetic induction.   An image forming apparatus comprising the fixing device according to claim 1.

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