JP2012154993A - Fixing device and image forming apparatus including the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fixing device including a rotation detection mechanism capable of accurately detecting the rotation of a roller, even when gear teeth slide over each other due to the engagement failure of gears and to provide an image forming apparatus including the fixing device.SOLUTION: A rotation detection mechanism 60 comprises a large-diameter gear 35 fixed to a fixing roller 131, a first idle gear 37 engaged with the large-diameter gear 35, a second idle gear 39 engaged with the first idle gear 37, an actuator gear 40 engaged with the second idle gear 39, and a rotation detection sensor 41 arranged to face the actuator gear 40. The first idle gear 37 comprises a first gear member 37a engaged with the large-diameter gear 35 and a second gear member 37b engaged with the second idle gear 39 and the first gear member 37a and the second gear member 37b have a rotation backlash larger than a rotation angle corresponding to one tooth of a drive input gear 30. The second idle gear 39 is pressed in a rotation axis direction by a coil spring 42.

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.

  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.

  To achieve the above object, the present invention provides a heated rotating body heated by a heating means, a drive input gear for inputting a driving force to the heated rotating body, and an output side fixed to the heated rotating body. A gear, an actuator gear having a light shielding plate formed on the outer peripheral surface thereof rotated by the driving force of the output gear, an optical sensor for detecting opening or blocking of an optical path by the light shielding plate of the actuator gear, and one end of the output A gear train composed of a plurality of idle gears connected to the side gear and connected to the actuator gear at the other end, and a rotation detection mechanism for detecting whether the heated rotating body is rotating, The at least one of a plurality of idle gears constituting the gear train includes a first gear member to which a gear on the upstream side in the drive transmission direction is coupled, and the first gear. A second gear member that is formed adjacent to the axial direction of the member and rotates integrally with the first gear member while meshing with a gear on the downstream side in the drive transmission direction; The idle gear connected to the downstream side in the drive transmission direction of the second gear member, or a rotation play larger than the rotation angle corresponding to one tooth of the drive input gear is provided between the two gear members. At least one of the actuator gears is provided with a reverse rotation preventing means.

  According to the present invention, in the fixing device having the above configuration, the optical sensor detects the rotation of the heated rotating body when detecting the opening or blocking of the optical path by the light shielding plate a plurality of times within a predetermined time. It is said.

  According to the present invention, in the fixing device having the above-described configuration, a reverse rotation prevention unit is provided on any idle gear or the actuator gear connected to the downstream side in the drive transmission direction of the second gear member. Yes.

  According to the present invention, in the fixing device configured as described above, the heating unit is an induction heating unit that heats the rotating body to be heated from the outside by electromagnetic induction.

  The present invention is also an image forming apparatus including the fixing device having the above-described configuration.

  According to the first configuration of the present invention, at least one of the idle gears disposed between the output side gear fixed to the heated rotating body and the actuator gear is connected to the first gear member and the second gear member. An actuator is provided when tooth skipping of the drive input gear occurs by dividing and providing a rotation play larger than the rotation angle corresponding to one tooth of the drive input gear between the first gear member and the second gear member. The gear does not rotate or rotates at an angle smaller than the rotation angle corresponding to one tooth of the drive input gear at the maximum. Further, by providing a reverse rotation preventing means on at least one of the idle gear or the actuator gear connected to the downstream side in the drive transmission direction of the second gear member, even if the first gear member rotates forward and backward, the actuator gear Following the first gear member does not reversely rotate. Therefore, in the optical sensor, opening or blocking of the optical path by the light shielding plate is not detected, or is detected only once, and erroneous detection of rotation of the heated rotating body can be reliably prevented.

  According to the second configuration of the present invention, in the fixing device having the first configuration, the optical sensor detects the rotating body to be heated when the optical path is detected by the light shielding plate multiple times within a predetermined time. Therefore, even if the actuator gear slightly rotates and the opening or blocking of the optical path by the light shielding plate is detected once, it is erroneously detected that the heated rotating body has rotated. Absent. Therefore, erroneous detection of the rotation of the heated rotating body can be prevented more reliably.

  According to the third configuration of the present invention, in the fixing device having the first or second configuration, an induction heating unit that heats the rotating body to be heated from the outside by electromagnetic induction is used as a heating unit. The detection accuracy of the rotation of the heated rotating body can be improved while shortening the up time and saving energy.

  Further, according to the fourth configuration of the present invention, by mounting the fixing device having any one of the first to third configurations, the heated rotation by heating the heated rotating body in a stopped state. The image forming apparatus is excellent in safety without fear of thermal deformation, smoke generation, or ignition of the body.

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. Exploded perspective view of the first idle gear constituting the rotation detection mechanism Schematic side view showing how the rotation of the fixing roller 131 is detected by the rotation detection mechanism 60 Schematic side view showing operation of rotation detection mechanism when tooth skipping occurs

  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 section 14, the paper P is distributed from the rear end of the paper P to the double-side 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. 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. Further, a rotation detection sensor 41 is disposed so as to face the actuator gear 40. The first idle gear 37, the second idle gear 39, the actuator gear 40, and the rotation detection sensor 41 constitute a rotation detection mechanism 60 (see FIG. 6) of the fixing roller 131.

  A plurality of light shielding plates 40 a for switching the rotation detection sensor 41 between ON and OFF are fixed on the outer peripheral surface of the actuator gear 40 at equal intervals. A coil spring 42 is attached to the rotation shaft of the second idle gear 39, and the second idle gear 39 is pressed in the direction of the rotation shaft by the urging force of the coil spring 42.

  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.

  FIG. 5 is an exploded perspective view of the first idle gear 37. The first idle gear 37 is divided into two in the axial direction: an inner first gear member 37a that meshes with the large-diameter gear 35 and an outer second gear member 37b that meshes with the second idle gear 39. A bearing hole 47 into which the rotation shaft is slidably inserted and a pair of ribs 50a formed in an arc shape around the bearing hole 47 are formed in the first gear member 37a. The second gear member 37b is also formed with a bearing hole 47 and a pair of ribs 50b having the same shape as the first gear member 37a.

  And the 1st gear member 37a and the 2nd gear member 37b are piled up so that the rib 50a and the rib 50b may mutually mesh, and it is mounted | worn with the rotating shaft. Further, when the rib 50a and the rib 50b are engaged with each other, a predetermined gap is formed between the rib 50a and the rib 50b. Thereby, the 1st gear member 37a and the 2nd gear member 37b have the rotation play of a predetermined angle (here 30 degrees).

  The rotation detection sensor 41 is a PI (photo interrupter) sensor in which a detection unit including a light emitting unit and a light receiving unit is provided on the opposed inner surfaces of a U-shape in plan view. When the light shielding plate 40a blocks the optical path of the detection unit, the light reception signal level of the detection unit is switched from HIGH to LOW, and the rotation of the fixing roller 131 can be detected. 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.

  Next, the operation of the rotation detection mechanism used in the fixing device of the present invention will be described in detail. 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 gear member 37a of the first idle gear 37 that meshes with the large-diameter gear 35 rotates in the clockwise direction in FIG. Then, the rib 50a of the first gear member 37a presses the rib 50b of the second gear member 37b in the rotation direction (clockwise), so that the second gear member 37b also rotates in the clockwise direction. Here, since the biasing force of the coil spring 42 is set to such an extent that the rotation of the second idle gear 39 by the second gear member 37b is not hindered, the second idle gear 39 meshing with the second gear member 37b is shown in FIG. The actuator gear 40 that rotates clockwise and meshes with the second idle gear 39 rotates clockwise in FIG.

  Then, since the light shielding plate 40a passes through the detection unit of the rotation detection sensor 41 due to the rotation of the actuator gear 40, a detection signal is transmitted from the rotation detection sensor 41 to the control unit, and the rotation of the fixing roller 131 is detected.

  Note that the rotation detection sensor 41 detects the rotation of the fixing roller 131 when it detects a switching portion (edge) of the received light signal level from HIGH to LOW a plurality of times (here, twice or more in 300 msec) within a predetermined time. To do. Further, when an edge is detected at an interval of 2.5 msec or more, it is recognized that there is a detection. As a result, it is possible to detect good rotation both when the rotation speed of the fixing roller pair 13a is full speed (during normal printing) and half speed (when printing on a photographic document or cardboard).

  FIG. 7 is a schematic side view showing the operation of the rotation detection mechanism when tooth skipping occurs between the drive input gear 30 and the roller drive gear 31. 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.

  Here, if the rotation backlash angle between the first gear member 37a and the second gear member 37b is set to be larger than the rotation angle of the first gear member 37a when the tooth jump occurs, the first gear jump occurs when the tooth jump occurs. The drive transmission from the gear member 37a to the second gear member 37b can be absorbed by the rotation backlash. As a result, the second idle gear 39 that meshes with the second gear member 37b and the actuator gear 40 that meshes with the second idle gear 39 do not rotate, or even if they rotate, the rotation angle is restricted.

  For example, if the number of teeth of the drive input gear 30 is 25 and the rotation ratio of the drive input gear 30 and the first idle gear 37 is 1: 0.85, the drive input gear 30 will have tooth skipping by one tooth. In this case, the rotation angle of the drive input gear 30 is 360/25 = 14.4 °, and the rotation angle of the first idle gear 37 at that time is 14.4 × 0.85 = 12.24 °. Therefore, if the rotation backlash angle between the first gear member 37a and the second gear member 37b is set to be larger than 12.24 °, the drive transmission from the first gear member 37a to the second gear member 37b is absorbed. Thus, the rotation of the actuator gear 40 can be prevented or the rotation angle can be regulated.

  Further, since the second idle gear 39 is pressed in the axial direction by the coil spring 42, the effect of preventing the erroneous detection of the rotation detection sensor 41 due to the backlash between the first gear member 37a and the second gear member 37b is the first effect. It is expressed regardless of the relative position of the rib 50a of the gear member 37a and the rib 50a of the second gear member 37b.

  For example, when tooth skip occurs in a state where the rib 50 a is in contact with the upstream side of the rotation direction of the rib 50 b as shown in FIG. 7, the rib 50 b is pressed against the rib 50 a and the second gear member 37 b is It rotates by an angle corresponding to the tooth (here, 12.24 °). At this time, depending on the rotation position of the actuator gear 40, the light shielding plate 40 a blocks or opens the detection unit of the rotation detection sensor 41, so that the edge is detected by the rotation detection sensor 41.

  However, since the second idle gear 39 meshing with the second gear member 37 b is pressed in the axial direction by the coil spring 42 and free rotation is restricted, the second gear member 37 b corresponds to one tooth of the drive input gear 30. 12. Stop at a position rotated by 24 °. That is, even if the first gear member 37a rotates forward and backward (oscillates) due to tooth skipping, the drive transmission is absorbed by the rotation play so that the second idle gear 39 does not swing following the first gear member 37a. It has become. Therefore, since the actuator gear 40 also stops without swinging, the edge is always detected only once by the rotation detection sensor 41, and it is not erroneously detected that the fixing roller 131 has rotated.

  As described above, according to the configuration of the present invention, the first idle gear 37 from the fixing roller 132 to the actuator gear 40 is divided into two in the axial direction so as to have a rotational play, so that the teeth of the drive input gear 30 can be obtained. It is possible to reliably prevent erroneous detection of the rotation of the fixing roller 131 when the jump 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 that case, one of the idle gears is divided into a first gear member and a second gear member, and a coil spring 42 is disposed on any of the idle gears connected to the downstream side of the drive transmission direction of the divided idle gear. Thus, the reverse rotation of the actuator gear 40 may be prevented. Alternatively, a coil spring 42 can be disposed on the actuator gear 40 itself to prevent reverse rotation.

  Further, instead of arranging the coil spring 42, the second idle gear 39 or the actuator gear 40 may be a one-way gear capable of transmitting the drive only in one direction.

  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 as shown in FIG. 1, and can be applied to various image forming apparatuses including a fixing device such as a monochrome copying machine, a digital multifunction machine, a facsimile machine, and a laser printer. .

  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 37a first gear member 37b second gear member 39 second idle gear 40 actuator gear 40a light shielding plate 41 rotation detection sensor (optical sensor)
42 Coil spring (reverse rotation prevention means)
60 Rotation detection mechanism 100 Color printer

Claims (4)

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 light shielding plate formed on an outer peripheral surface that is rotated by a driving force of the output side gear, and an optical path opened or blocked by the light shielding plate of the actuator gear. An optical sensor for detecting, and a gear train composed of a plurality of idle gears having one end connected to the output gear and the other end connected to the actuator gear, and the heated rotating body rotates. A rotation detection mechanism for detecting whether or not,
In a fixing device having
At least one of the plurality of idle gears constituting the gear train is formed adjacent to the first gear member to which the gear on the upstream side in the drive transmission direction is connected, and the axial direction of the first gear member is formed and transmitted. Divided into a second gear member that rotates integrally with the first gear member while meshing with a gear on the downstream side in the direction,
A rotation play larger than a rotation angle corresponding to one tooth of the drive input gear is provided between the first gear member and the second gear member, and on the downstream side in the drive transmission direction of the second gear member. A fixing device characterized in that a reverse rotation preventing means is provided on any of the connected idle gears or the actuator gear.   The fixing device according to claim 1, wherein the optical sensor detects the rotation of the heated rotating body when detecting the opening or blocking of the optical path by the light shielding plate a plurality of times within a predetermined time.   The fixing device according to claim 1, wherein the heating unit is an induction heating unit that heats a heated rotating body from the outside by electromagnetic induction.   An image forming apparatus comprising the fixing device according to claim 1.