JP2016161676A - Fixing device and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To easily detect the occurrence of various types of malfunctions in a fixing device.SOLUTION: A fixing device of the present invention comprises: an endless belt for conveying a medium; a drive roller that has the belt laid thereover and rotates the belt; a driven roller that is pressed against the belt to have a rotation driving power to be transmitted thereto from the driving roller via the belt and is rotated with the belt; and a rotation detection part that detects the rotation of the driven roller. With this configuration, when various types of malfunctions occurs in the fixing device, the rotation detection part can detect the occurrence of the malfunctions as stoppage of the rotation or a change in rotation speed of the driven roller according to the type of the malfunction, and can easily detect the occurrence of various types of malfunctions in the fixing device.SELECTED DRAWING: Figure 8

Description

  The present invention relates to a fixing device and an image forming apparatus, and is suitably applied to, for example, a color electrophotographic printer (hereinafter also referred to as a color printer) and a fixing unit provided in the color printer.

  A conventional image forming apparatus is provided with a fixing roller driven by a driving motor in a fixing device, a heating roller having a heat source, an endless fixing belt, and a pressure roller, and fixing to the fixing roller and the heating roller. While the belt was stretched, the pressure roller was pressed against the fixing roller via the fixing belt. Therefore, in the image forming apparatus, when the fixing roller rotates in one direction in accordance with the operation of the drive motor, the heating roller and the fixing belt rotate in one direction in conjunction with the rotation, and the pressure roller rotates in the other direction. As a result, the sheet on which the toner image is transferred is heated and pressed between the fixing belt and the pressure roller to fix the toner image on the sheet. However, in the image forming apparatus, when the outer diameter of the fixing roller in the fixing device changes due to a temperature change, an operation failure in which the sheet conveyance speed changes occurs. Therefore, in the image forming apparatus, a thermistor is arranged in the cored bar portion of the fixing roller in the fixing device, and the fixing roller is changed by temperature change by controlling the drive motor based on the temperature detection result of the cored bar part by the thermistor. Even when the outer diameter is changed, the sheet conveyance speed in the fixing device is substantially constant (see, for example, Patent Document 1).

JP 2012-13821 A (page 9 to page 11, FIG. 2)

  By the way, in the conventional image forming apparatus, based on the detection result of the temperature of the cored bar portion of the fixing roller by the thermistor, occurrence of a malfunction in which the sheet conveyance speed changes is detected in the fixing apparatus. In addition to malfunctions that change the paper conveyance speed, malfunctions such as malfunctions that stop the rotation of the fixing belt, and malfunctions that cause the rotation of the pressure roller to stop while the fixing belt rotates. There are various things. However, the conventional image forming apparatus has a problem that even if various malfunctions occur in the fixing device, the malfunction is not detected except for the malfunction that changes the sheet conveyance speed.

  The present invention has been made in consideration of the above points, and an object of the present invention is to propose a fixing device and an image forming apparatus that can easily detect the occurrence of various malfunctions.

  In order to solve such a problem, in the present invention, an endless belt for conveying a medium, a driving roller for rotating the belt and rotating the belt, and pressing the belt against the fixing device are driven by the belt. A rotational driving force is transmitted from the roller via the belt, and a driven roller that rotates together with the belt and a rotation detector that detects the rotation of the driven roller are provided.

  Therefore, in the present invention, when various malfunctions occur in the fixing device, the occurrence of the malfunction is detected as a rotation stop of the driven roller or a change in the rotation speed according to the type of malfunction by the rotation detection unit. Can do.

  According to the present invention, an endless belt for transporting a medium to the fixing device, a driving roller that hangs the belt and rotates the belt, and is pressed against the belt to thereby rotate the driving force from the driving roller. Is transmitted through the belt and provided with a driven roller that rotates together with the belt and a rotation detector that detects the rotation of the driven roller, when various malfunctions occur in the fixing device, Occurrence can be detected by the rotation detection unit as a stop of rotation of the driven roller or a change in the rotation speed according to the type of malfunction, and thus a fixing device and image formation that can easily detect the occurrence of various malfunctions An apparatus can be realized.

1 is a schematic side view showing an internal configuration of a color printer according to the present invention. FIG. 3 is a schematic side view showing a configuration of a fixing unit. FIG. 6 is a schematic diagram for explaining transmission of a rotational driving force generated by a unit driving motor in a fixing unit. It is a rough-line side view with which it uses for description of generation | occurrence | production of the malfunctioning by the clogging of the medium to the clearance gap between a 1st belt and a isolation | separation part. It is a rough-line side view with which it uses for description of generation | occurrence | production of the malfunctioning by the biting part of the belt opening part to the clamping part. It is a rough side view with which it uses for description of generation | occurrence | production of the malfunctioning by the clogging of the medium in a clamping part. It is a rough-line side view with which it uses for description of generation | occurrence | production of the malfunctioning by the underpressure of the 2nd belt with respect to a 1st belt. FIG. 6 is a schematic perspective view illustrating a configuration of a rotation detection unit provided in the fixing unit. It is a rough-line side view which shows the structure (1) of the fixing unit by other embodiment. It is a rough-line side view which shows the structure (2) of the fixing unit by other embodiment. It is a rough-line side view which shows the structure (3) of the fixing unit by other embodiment.

The best mode for carrying out the invention (hereinafter, also referred to as an embodiment) will be described below with reference to the drawings. The description will be given in the following order.
(1) Embodiment (2) Other embodiments

(1) Embodiment (1-1) Internal Configuration of Color Printer In FIG. 1, reference numeral 1 denotes a primary transfer type color printer according to the present invention as a whole. The color printer 1 forms a print image on the surface of a plurality of types of rectangular media 2 such as plain paper and film. For example, the color printer 1 has a substantially square box shape in which the right end surface in the figure is the front surface 3A. A printer housing 3 is provided. Incidentally, in the following description, when the color printer 1 is viewed facing the front surface 3A of the printer housing 3, the direction above the color printer 1 indicated by the arrow a1 in the figure is also referred to as the printer upward direction, which is the opposite. Is also referred to as the downward direction of the printer, and when there is no need to distinguish these directions, they are collectively referred to as the upward and downward direction of the printer. Further, in the following description, the direction in front of the color printer 1 indicated by the arrow b1 in the figure when the color printer 1 is viewed facing the front surface 3A of the printer housing 3 is also referred to as the front direction of the printer. Is also referred to as the rear direction of the printer, and when there is no need to distinguish between these directions, they are also collectively referred to as the front-rear direction of the printer. Furthermore, in the following description, the left direction of the color printer 1 indicated by the arrow c1 in the figure when the color printer 1 is viewed facing the front surface 3A of the printer housing 3 is also referred to as the printer left direction. The opposite direction is also referred to as the right direction of the printer, and when it is not necessary to distinguish between these, they are also collectively referred to as the printer left-right direction. The printer casing 3 has a medium delivery section 3BX that delivers the medium 2 on which the print image is formed at the rear end of the upper surface 3B, and a medium discharge that ejects the medium 2 from the printer casing 3 to the medium delivery section 3BX. An outlet 3BY is formed.

  In the printer casing 3, an image forming unit 5 for forming a print image on the surface of the medium 2 is disposed at the center, and the medium 2 is supplied to the image forming unit 5 at the lower end. A medium supply unit 6 is disposed for the purpose. The image forming unit 5 includes, for example, four image forming units 10 to 13, a transfer unit 15, and a fixing unit 16. The four image forming units 10 to 13 use toners of different colors such as black (K), yellow (Y), magenta (M), and cyan (C) as a developer for forming a print image. The configuration is the same except for. That is, the four image forming units 10 to 13 are charged on the surfaces of the photosensitive drums 20 to 23 as image bearing members provided so as to be able to rotate in one rotation direction indicated by an arrow d1 in the drawing. After being charged to a predetermined potential by thru 27, an electrostatic latent image is formed by exposure with LED (Light Emitting Diode) heads 28 through 31, and the electrostatic latent image is developed with toner by developing units 32 through 35. Thus, black, yellow, magenta, and cyan toner images are formed as developer images. For example, the four image forming units 10 to 13 are arranged in the order of forming a black toner image, a yellow toner image, a magenta toner image, and a cyan toner image in the rear direction of the printer. Yes.

  In the transfer unit 15, an endless transfer belt 40 is stretched between a belt driving roller 38 and a driven roller 39 that are rotatably provided in a rotation direction opposite to the one rotation direction, and four transfer rollers ( The surface of the four photosensitive drums 20 to 23 is pressed against the surface of the four photosensitive drums 20 to 23 via the transfer belt 40 with a predetermined pressing force. The color toner images are transferred so as to overlap one another in order. The fixing unit 16 is provided with various components in a substantially box-shaped unit casing 42 that is long in the left-right direction of the printer, and heats and pressurizes the medium 2 on which the four-color toner images are transferred. The toner image of 4 colors is fixed on the surface of 2 to form a color print image. Incidentally, the configuration of the fixing unit 16 will be described later. The medium supply unit 6 includes a medium cassette 44 in which a plurality of media 2 can be loaded, and a feeding roller (not shown) for feeding the media 2 from the medium cassette 44 one by one. In the printer housing 3, a medium supply transport unit 45 that forms a medium supply transport path for transporting the medium 2 fed from the medium cassette 44 to the image forming unit 5 is disposed at the front lower end. Yes. Further, in the printer casing 3, a medium discharge transport unit 46 that forms a medium discharge transport path for transporting the medium 2 fed from the fixing unit 16 to the medium discharge port 3BY is disposed at the rear upper end. Yes.

  In the printer housing 3, for example, a control unit 48 such as a microprocessor for overall control of the color printer 1 is provided. The control unit 48 drives and controls each unit in the printer casing 3 at the time of forming a print image, so that the medium 2 is fed out from the medium cassette 44 one by one to the image forming unit 5 through the medium supply conveyance path. Transport. The control unit 48 controls driving of the four LED heads 28 to 31 in the four image forming units 10 to 13 in accordance with, for example, the black, cyan, magenta, and yellow color components of the print target image based on the image data. As a result, four color toner images are formed on the surfaces of the photosensitive drums 20 to 23 as described above. Therefore, the control unit 48 continues to convey the medium 2 conveyed to the image forming unit 5 through the medium supply conveyance path by the four photosensitive drums 20 to 23 and the transfer belt 40, and the four photosensitive drums 20. To 23, the toner images on the medium 2 are transferred to the surface of the medium 2 through four transfer rollers in order, and then the four color toner images are fixed on the surface of the medium 2 by the fixing unit 16. A print image is formed, and the medium 2 is conveyed to the medium discharge port 3BY via the medium discharge conveyance path and discharged to the medium delivery unit 3BX.

(1-2) Configuration of Fixing Unit Next, the configuration of the fixing unit 16 will be described with reference to FIG. As shown in FIG. 2, the fixing unit 16 has the unit casing 42 as described above. The unit housing 42 has a medium intake port 42AX that is long in the left-right direction of the printer at the center of the housing front plate portion 42A located on the upstream side in the medium transport direction according to the medium transport direction at the time of printing image formation. Is formed. Further, the unit housing 42 is arranged at the center of the housing rear plate portion 42B located downstream of the housing front plate portion 42A in the medium conveying direction in accordance with the medium conveying direction at the time of printing image formation. A medium discharge port 42BX that is long in the left-right direction is formed. A heating unit 50 for heating the medium 2 and a pressurizing unit 51 for pressurizing the medium 2 together with the heating unit 50 are provided adjacent to each other in the unit casing 42. The heating unit 50 includes a driving roller 53, a driven roller (hereinafter also referred to as a first driven roller) 54, and an endless belt (hereinafter also referred to as a first belt) 55 for conveying the medium 2. And a heater 56 which is a halogen lamp. The drive roller 53 is provided with a drive roller shaft in a roller body having a predetermined outer diameter. The drive roller 53 is provided at one end and the other end in the longitudinal direction of the drive roller shaft at predetermined opposing positions near the center of the rear end of the unit case 42 on the case left side plate and case right side plate (not shown). Are attached to a pair of first bearing portions (not shown). As a result, the drive roller 53 makes one rotation around the drive roller shaft parallel to the left-right direction of the printer via the unit left side plate and the case right side plate at a predetermined position downstream in the medium conveyance direction by the unit case 42. It is supported so that it can rotate in the direction. The first driven roller 54 is provided with a first driven roller shaft on a roller body having a predetermined outer diameter that is thicker than the outer diameter of the driving roller 53, for example. The first driven roller 54 has a pair of one end portion and the other end portion in the longitudinal direction of the first driven roller shaft provided at predetermined facing positions near the center of the front end portion of the case left side plate and case right side plate. It is attached to a second bearing portion (not shown). As a result, the first driven roller 54 is moved by the unit casing 42 at a predetermined position on the upstream side in the medium transport direction from the position where the driving roller 53 is disposed (that is, the position on the front side of the driving roller 53). A plate is supported so as to be able to rotate in one rotation direction around a first driven roller shaft parallel to the left-right direction of the printer.

  Further, the first belt 55 is formed by selecting a material, a thickness, and the like as appropriate so that the heat capacity is relatively small as compared with the driving roller 53 and the first driven roller 54 and the temperature can be quickly raised during heating. The first belt 55 has a belt circumferential length selected to be a predetermined length that is relatively longer than twice the arrangement interval between the driving roller 53 and the first driven roller 54 positioned in the front-rear direction. The first belt 55 includes a pair of first belt engaging portions (one belt opening portion and the other belt opening portion provided at predetermined opposing positions on the upper end portions of the housing left side plate and the housing right side plate). (Not shown). Thus, the arrangement position of the first belt 55 is restricted by the pair of first belt engaging portions so as not to be shifted as much as possible in the lateral direction of the pudding, and no tension is applied to the driving roller 53 and the first driven roller 54. It is hung in a state. That is, the first belt 55 has a rear lower portion of the belt inner surface in contact with a lower portion of the outer peripheral surface of the driving roller 53 and a front lower portion of the first belt 55 in contact with a lower portion of the outer peripheral surface of the first driven roller 54. Thus, the driving roller 53 and the first driven roller 54 are arranged so as to be spaced apart from the outer peripheral surface of the driving roller 53 and the first driven roller 54 from the front side portion to the rear side portion. The heater 56 has a pair of terminal holding portions (not shown) in which the one end side terminal portion and the end side terminal portion in the heater longitudinal direction are provided at predetermined opposing positions on the upper end portion of the case left side plate and case right side plate. ). As a result, the heater 56 is located on the inner side of the first belt 55 so that the heater longitudinal direction is parallel to the printer left-right direction, as far as possible from the driving roller 53 and the first driven roller 54, and close to the upper portion of the inner surface of the belt. Are arranged.

  On the other hand, the pressure unit 51 has a pair of driven rollers 58 and 59. In the following description, one driven roller 58 of the pair of driven rollers 58 and 59 is also referred to as a second driven roller 58, and the other driven roller 59 is also referred to as a third driven roller 59. The pressurizing unit 51 also has an endless belt (hereinafter also referred to as a second belt) 60 for conveying the medium 2. The second driven roller 58 is provided with a second driven roller shaft on a roller body having an outer diameter substantially equal to the outer diameter of the driving roller 53, for example. Further, the unit housing 42 has a pair of third bearing portions (not shown) at a predetermined facing position near the center of the rear end portion, which is directly below the pair of first bearing portions in the housing left side plate and the housing right side plate. Is provided to be displaceable in the vertical direction of the printer. The second driven roller 58 has one end portion and the other end portion in the longitudinal direction of the second driven roller shaft attached to a pair of third bearing portions provided on the case left side plate and the case right side plate. As a result, the second driven roller 58 can be displaced in the vertical direction of the printer through the unit left side plate and the right side plate at a predetermined position just below the drive roller 53 on the downstream side in the medium conveyance direction by the unit case 42. In addition, the second driven roller shaft parallel to the horizontal direction of the printer is supported so as to be rotatable in other rotational directions. The third driven roller 59 is provided with a third driven roller shaft on a roller body having an outer diameter substantially equal to the outer diameter of the first driven roller 54, for example. Further, the unit housing 42 has a pair of fourth bearing portions (not shown) at a predetermined facing position near the center of the front end portion, which is directly below the pair of second bearing portions in the housing left side plate and the housing right side plate. The printer is provided to be displaceable in the vertical direction. The third driven roller 59 has one end portion and the other end portion in the longitudinal direction of the third driven roller shaft at a pair of fourth bearing portions (not shown) provided on the case left side plate and the case right side plate. It is attached. As a result, the third driven roller 59 is moved to a predetermined position (that is, the second driven roller 58 of the second driven roller 58) immediately below the first driven roller 54, which is upstream of the arrangement position of the second driven roller 58 with respect to the medium transport direction. Centered on a third driven roller shaft that is displaceable in the vertical direction of the printer via the housing left side plate and the case right side plate at the front side and a position directly below the first driven roller 54 and parallel to the printer horizontal direction. It is supported so as to be rotatable in other rotational directions.

  Further, the second belt 60 is formed in the same manner as the first belt 55, and one belt opening and the other belt opening are a pair of first belt engaging portions in the case left side plate and case right side plate. Is engaged with a pair of second belt engaging portions (not shown) provided at a predetermined facing position of the lower end portion that is directly below the lower end portion. As a result, the second belt 60 is regulated by the pair of second belt engaging portions so that the position of the second belt 60 is not shifted as much as possible in the left-right direction of the pudding, and the second driven roller 58 is positioned just below the first belt 55. The third driven roller 59 is hung in a state where no tension is applied. That is, the second belt 60 has a rear upper portion on the inner surface of the belt in contact with an upper portion of the outer peripheral surface of the second driven roller 58 and a front upper portion in contact with an upper portion of the outer peripheral surface of the third driven roller 59. A portion from the front side portion to the rear side portion passing through the lower side portion is arranged to be separated from the outer peripheral surfaces of the second driven roller 58 and the third driven roller 59. However, the housing left side plate and the housing right side plate have biasing portions such as compression coil springs that bias the pair of third bearing portions and the pair of fourth bearing portions so as to be displaced upward in the printer, respectively. Is provided. Therefore, the pressurizing unit 51 passes the upper part of the outer peripheral surface of the second driven roller 58 below the outer peripheral surface of the driving roller 53 through the rear upper part of the second belt 60 and the rear lower part of the first belt 55 in order. The side part is pressed with a predetermined pressing force. Further, the pressing unit 51 is configured so that the upper portion of the outer peripheral surface of the third driven roller 59 is passed through the front upper portion of the second belt 60 and the front lower portion of the first belt 55 in order. It is pressed against the lower part with a predetermined pressing force. As a result, the pressing unit 51 moves from the pressing position of the first driven roller 54 and the third driven roller 59 on the upstream side in the medium conveying direction to the pressing position of the driving roller 53 and the second driven roller 58 on the downstream side in the medium conveying direction. The sandwiching portion 61 for transporting the medium 2 while sandwiching it for heating and pressurization is formed by the flat lower portion of the first belt 55 and the flat upper portion of the second belt 60. Incidentally, a substantially L-shaped plate-like separation part 62 for separating the medium 2 from the belt outer surface of the first belt 55 is provided at the rear side of the sandwiching part 61 in the unit casing 42 with a sharp tip. The portion is disposed close to the rear lower side portion of the outer surface of the first belt 55.

  The drive roller 53 includes a plurality of gears (not shown) on the output shaft of a unit drive motor (not shown) provided in the printer housing 3 at one end or the other end of the drive roller shaft. ) In order. The heater 56 is electrically connected to a heater power source (not shown) provided in the printer housing 3 through one end side terminal portion and the other end side terminal portion. Further, a temperature sensor 63 such as a thermistor for detecting the temperature of the first belt 55 in a non-contact manner is disposed in a predetermined position in the unit housing 42 so as to face the belt outer surface of the first belt 55. ing. The temperature sensor 63 is electrically connected to the control unit 48, for example. As a result, the control unit 48 detects the temperature of the first belt 55 via the temperature sensor 63 in the fixing unit 16 during the formation of the print image, and appropriately energizes the heater 56 by the heater power supply according to the detection result. The heater 56 is caused to generate heat while performing on / off control. Further, the control unit 48 starts operating the unit drive motor almost at the same time as the start of heat generation of the heater 56, thereby rotating the drive roller 53 in one rotation direction in response to this, and interlocking with the rotation, the first belt. 55 and the first driven roller 54 are also rotated in one rotation direction. In addition, the control unit 48 rotates the second driven roller 58 and the third driven roller 59 together with the second belt 60 in the other rotation direction in conjunction with the rotation of the first belt 55 in the one rotation direction. As a result, the controller 48 causes the heater 56 to appropriately generate heat while rotating the first belt 55 in one rotation direction in the fixing unit 16 to heat the entire first belt 55 to a desired temperature. In this state, when the medium 2 on which the toner images for four colors have been transferred to the surface from the four image forming units 10 to 13 and the transfer unit 15 side is transferred to the fixing unit 16. It takes in in the unit housing | casing 42 through opening 42AX. As a result, the fixing unit 16 is heated and pressurized while being conveyed so that the medium 2 is sandwiched by the sandwiching portions 61 of the first belt 55 and the second belt 60 in the unit casing 42, so that the surface of the medium 2 is The four color toner images are once melted and fixed to form a color print image. Then, the fixing unit 16 discharges the medium 2 on which the print image is formed from the inside of the unit housing 42 through the medium discharge port 42BX, transfers it to the medium discharge conveyance path, and thus conveys the medium 2 to the medium discharge port 3BY. be able to. In this way, the fixing unit 16 can form a color print image on the surface of the medium 2.

  Incidentally, in the fixing unit 16, as described above, the first belt 55 is pressed against the driving roller 53 that is only connected to the unit driving motor, and the first driven roller 54 is pressed against the first belt 55. In the fixing unit 16, the second belt 60 is also pressed against the first belt 55, and the second driven roller 58 and the third driven roller 59 are pressed against the second belt 60. Therefore, as shown in FIG. 3, in the fixing unit 16, when a print image is formed, a driving force for rotation is applied to the driving roller 53 by the rotation of the output shaft from the unit driving motor 65 (hereinafter also referred to as a rotational driving force). When F1 is given, the drive roller 53 rotates in one rotation direction in response thereto. The rotational driving force F1 applied to the driving roller 53 is transmitted to the first belt 55 by the rotation of the driving roller 53 in one rotation direction. Thereby, the first belt 55 rotates in one rotation direction together with the drive roller 53. The rotational driving force F1 transmitted from the driving roller 53 to the first belt 55 is further transmitted to the first driven roller 54 by the rotation of the first belt 55 in one rotation direction. As a result, the first driven roller 54 rotates in one rotation direction together with the first belt 55. Further, the rotational driving force F1 transmitted from the drive roller 53 to the first belt 55 is also transmitted to the second belt 60 by the rotation of the first belt 55 in one rotation direction. As a result, the second belt 60 rotates in the other rotation direction opposite to the rotation direction of the first belt 55. Furthermore, the rotational driving force F1 transmitted from the driving roller 53 to the second belt 60 via the first belt 55 is caused by the rotation of the second belt 60 in the other rotational direction, thereby generating the second driven roller 58 and the third driven roller. It is transmitted to the roller 59. As a result, the second driven roller 58 and the third driven roller 59 rotate in the other rotation direction together with the second belt 60. In the following description, a transmission path for sequentially transmitting the rotational driving force F1 generated by the unit driving motor 65 from the driving roller 53 to the first belt 55 and the first driven roller 54, and from the driving roller 53 to the first belt 55. The transmission path for transmitting to the second driven roller 58 and the third driven roller 59 via the second belt 60 in order is also called a driving force transmission path. Thus, in the fixing unit 16, the first belt 55 and the second belt 60 are rotated in opposite rotation directions based on the driving roller 53 by the rotational driving force F <b> 1 generated by the operation of the unit driving motor 65, Thus, the medium 2 can be heated and pressurized while being conveyed by the sandwiching unit 61.

  However, in the fixing unit 16, an operation failure that does not normally operate for forming a print image may occur due to deterioration of each part or quality of the medium 2 used for forming a print image. Therefore, in the following, some examples of malfunctions occurring in the fixing unit 16 will be described. First, when forming a print image, the fixing unit 16 sandwiches the medium 2 from the upstream side in the medium transport direction by sandwiching the medium 2 in the sandwiching unit 61 with the surface on which the toner images for four colors are transferred facing upward. The toner image for the four colors transferred to the outer surface of the first belt 55 is brought into contact with the surface of the medium 2 along with the surface of the medium 2. Thereby, the fixing unit 16 directly heats and melts the toner image on the surface of the medium 2 by the first belt 55. When the toner image on the surface of the medium 2 melts, the fixing unit 16 separates the melted toner image by peeling the medium 2 from the outer surface of the first belt 55 by the separation unit 62 because the melted toner image has a certain viscosity. doing. However, as shown in FIG. 4, in the fixing unit 16, for example, if the waist of the medium 2 sandwiched between the sandwiching portions 61 is relatively weak, the medium 2 cannot be separated from the outer surface of the first belt 55. In some cases, the belt enters the gap between the belt outer surface and the separation portion 62 and becomes clogged. In this case, in the fixing unit 16, the medium 2 jammed in the gap between the outer surface of the belt and the separation unit 62 becomes a rotational load on the first belt 55. Therefore, in the fixing unit 16, the rotation of the first belt 55 is stopped (and the rotation of the first driven roller 54 is stopped as the rotation of the first belt 55 is stopped), and the rotation of the first belt 55 is stopped. Transmission of the rotational driving force F <b> 1 to the second belt 60 is interrupted, and a malfunction occurs in which the rotation of the second driven roller 58 and the third driven roller 59 together with the second belt 60 is stopped.

  Further, as shown in FIG. 5, in the fixing unit 16, for example, if one of the left and right ends of the medium 2 sandwiched in the sandwiching section 61 is bent, the thickness of the entire medium 2 differs between the left and right. In some cases, the first belt 55 and the second belt 60 are displaced from the original arrangement position while being rotated and pulled toward the other unbent end portion of the medium 2. In the fixing unit 16, the first belt 55 and the second belt 60 press the belt opening portions against the first belt engaging portion and the second belt engaging portion so that at least a part of the belt opening portions is rolled. May be bent. In this case, in the fixing unit 16, the bent portions 55 </ b> A and 60 </ b> A of the belt opening portions of the first belt 55 and the second belt 60 are engaged with the sandwiching portion 61, and the bent portions 55 </ b> A and 60 </ b> A are engaged with the first belt 55. Rotational load against Therefore, in the fixing unit 16, the rotation of the first belt 55 is stopped (and the rotation of the first driven roller 54 is stopped as the rotation of the first belt 55 is stopped), and the rotation of the first belt 55 is stopped. Transmission of the rotational driving force F <b> 1 to the second belt 60 is interrupted, and a malfunction occurs in which the rotation of the second driven roller 58 and the third driven roller 59 together with the second belt 60 is stopped.

  Further, as illustrated in FIG. 6, in the fixing unit 16, for example, if a plurality of wrinkles are generated in the medium 2 sandwiched between the sandwiching portions 61, the sandwiching portion 61 may be clogged with the media 2. In this case, in the fixing unit 16, if the medium 2 is caught in the outer surface of the first belt 55 or the outer surfaces of both the first belt 55 and the second belt 60, The medium 2 jammed in the sandwiching portion 61 becomes a rotational load on the first belt 55. Therefore, in the fixing unit 16, the rotation of the first belt 55 is stopped (and the rotation of the first driven roller 54 is stopped as the rotation of the first belt 55 is stopped), and the rotation of the first belt 55 is stopped. Transmission of the rotational driving force F <b> 1 to the second belt 60 is interrupted, and a malfunction occurs in which the rotation of the second driven roller 58 and the third driven roller 59 together with the second belt 60 is stopped. In this case, in the fixing unit 16, if the medium 2 is caught on the outer surface of the second belt 60 so that the medium 2 is jammed, the first belt 55 slides the outer surface of the belt with respect to the medium 2. However, the transmission of the rotational driving force F1 to the second belt 60 due to the rotation of the first belt 55 is interrupted by the medium 2 jammed in the sandwiching portion 61. An operation failure occurs in which the rotation of the second driven roller 58 and the third driven roller 59 stops.

  Further, as shown in FIG. 7, in the fixing unit 16, for example, if the biasing portions that bias the pair of third bearing portions and the pair of fourth bearing portions do not function normally due to deterioration or the like, the second driven roller 58. In some cases, the third driven roller 59 cannot be pressed against the driving roller 53 and the first driven roller 54 through the second belt 60 and the first belt 55 sequentially with a predetermined pressing force. In this case, in the fixing unit 16, the first driven roller 54 rotates together with the first belt 55 according to the rotation of the driving roller 53, but the belt outer surface of the first belt 55 slips with respect to the belt outer surface of the second belt 60. As a result, the rotational driving force F1 cannot be transmitted from the first belt 55 to the second belt 60, and the second belt 60 and the second driven roller 58 and the third driven roller 59 stop rotating together with the second belt 60. . In the fixing unit 16, when some of the malfunctions described above occur, depending on the type, the rotation of the first belt 55 stops. The rotation of the third driven roller 59 stops. In addition to this, in the fixing unit 16, for example, when the pair of first bearing portions and the pair of third bearing portions, the pair of second bearing portions and the pair of fourth bearing portions are deteriorated, the sandwiching portion 61. The first belt 55 and the second belt 60 rotate at a prescribed rotational speed until the medium 2 is sandwiched between the two, but when the medium 2 is sandwiched between the sandwiching portions 61, the medium 2 is driven by the drive roller 53 and the second belt 60. A rotational load is applied to the driven roller 58, the first driven roller 54, and the third driven roller 59, along with the rotational speeds of the drive roller 53 and the second driven roller 58, and the first driven roller 54 and the third driven roller 59. In some cases, the rotational speeds of the first belt 55 and the second belt 60 may be lower (slower) than a predetermined rotational speed. In this case, in the fixing unit 16, an operation failure occurs in which the medium conveyance speed decreases in the sandwiching portion 61 formed by the first belt 55 and the second belt 60. As described above, various malfunctions occur in the fixing unit 16.

  For this reason, as shown in FIG. 8, the fixing unit 16 includes, for example, the third driven roller 59 located on the most downstream side in the driving force transmission path from the driving roller 53 to the second driven roller 58 and the third driven roller 59. In order to detect this rotation, a rotation detecting unit 72 including a rotating body 70 and a photosensor 71 is provided. In the rotating body 70, for example, on the outer periphery of the central disk-shaped roller mounting portion, four flat blades radially radiate at equal intervals toward the same central axis as the surface of the roller mounting portion. Projected. The rotating body 70 is formed so that the width of the tip of each of the four blades is equal to the distance between the tips of adjacent blades, and the reflectance is increased on the surface of the four blades. For this purpose, a predetermined mirror finish is applied. In the photosensor 71, a light emitting element and a light receiving element are provided with their light emitting surface and light receiving surface directed in the same direction. Further, in the third driven roller 59, the tip end portion of the journal portion 59A of the third driven roller shaft protrudes outside the housing left side plate of the unit housing 42 via the fourth bearing portion (not shown). . The rotating body 70 has a roller mounting portion fixed to the end surface of the journal portion 59 </ b> A of the third driven roller 59. Accordingly, the rotating body 70 is provided so as to rotate integrally with the third driven roller 59 with the surfaces of the four blades facing left. The photosensor 71 is attached to, for example, a sensor attachment portion (not shown) provided on the outer surface of the housing left side plate. Thus, the photosensor 71 causes the light emitting surface of the light emitting element and the light receiving surface of the light receiving element to face the positions where the tip portions of the four blades sequentially pass when the rotating body 70 rotates together with the third driven roller 59. Yes. The photo sensor 71 is electrically connected to the control unit 48 described above. As a result, the photosensor 71 emits rotation detection light by the light emitting element under the control of the control unit 48 when the print image is formed, and when the rotation detection light passes between adjacent blades of the rotating body 70. Although no light is received by the light receiving element, when the rotation detection light is reflected by the surface of the blade of the rotating body 70, the obtained reflected light can be received by the light receiving element. The photosensor 71 sends a rotation detection signal to the control unit 48 while emitting the rotation detection light by the light emitting element, and the signal level of the rotation detection signal is determined when the reflected light is received by the light receiving element. It rises to a logic “H” level, and falls to a logic “L” level when no reflected light is received by the light receiving element.

  Therefore, when the rotating body 70 is rotating together with the third driven roller 59, the photosensor 71 sequentially repeats light reception and non-light reception of the reflected light by the light receiving element while emitting the rotation detection light by the light emitting element. As a result, a pulse-shaped rotation detection signal for alternately changing the signal level between the logic “H” level and the logic “L” level in accordance with the rotation speed of the third driven roller 59 is sent to the control unit 48. On the other hand, when the rotation of the rotating body 70 together with the third driven roller 59 stops, the photosensor 71 irradiates the surface of any blade of the rotating body 70 with the rotation detection light emitted by the light emitting element. In order to continue receiving the reflected light by the light receiving element, a rotation detection signal that does not change while the signal level is raised to the logic “H” level is sent to the control unit 48. When the rotation of the rotating body 70 is stopped together with the third driven roller 59, the photosensor 71 detects that the rotation detection light emitted by the light emitting element passes between adjacent blades of the rotating body 70. Since the reflected light is not received, a rotation detection signal that does not change while the signal level is lowered to the logic “L” level is sent to the control unit 48. Accordingly, the control unit 48 determines whether or not the rotation detection signal supplied from the photosensor 71 has a signal level change and a signal level change period (that is, from the time when the signal level rises to a logic “H” level) when a print image is formed. The time until the signal once falls to the logic “L” level and rises again to the logic “H” level is monitored.

  Then, the control unit 48 determines that the signal level of the rotation detection signal is logic “H” during an operation failure detection time corresponding to one cycle of a change in signal level when the third driven roller 59 is rotating normally, for example. If it does not change while rising to the level or falling to the logic “L” level, the rotation of the third driven roller 59 stops and it is detected that a malfunction has occurred. That is, the control unit 48 causes the malfunction of the rotation of both the first belt 55 and the second belt 60 due to the stop of the rotation of the third driven roller 59, or the second belt 60 while the first belt 55 rotates. It is detected that a malfunction has occurred that has stopped rotating. In addition, when the signal level of the rotation detection signal periodically changes, the control unit 48, for example, has a period during which the signal level rises to the logic “H” level during the malfunction detection time (or the signal level is logic “ When the period when the third driven roller 59 is rotating normally is longer than the period when the third driven roller 59 is rotating normally, the rotation speed of the third driven roller 59 is reduced (changed), resulting in malfunction. Detect that. That is, the control unit 48 detects that an operation failure has occurred in which the medium conveyance speed in the sandwiching unit 61 has decreased due to a change in the rotation speed of the third driven roller 59. In this way, the control unit 48 detects the occurrence of any of the various malfunctions described above in the fixing unit 16, and determines the occurrence of the malfunction by rotating the third driven roller 59 according to the type of malfunction. It can be detected as a stop or a change in rotational speed. The control unit 48 causes a malfunction to the user via, for example, a display unit or a speaker (not shown) provided in the color printer 1 or a host device such as a personal computer connected to the color printer 1. Notify you.

  By the way, the controller 48 causes the fixing unit 16 to malfunction when the rotation of both the first belt 55 and the second belt 60 stops, or to rotate the second belt 60 while the first belt 55 rotates. When an operation failure to stop occurs, it cannot be determined from the rotation detection signal which of these operation failures has occurred, and the rotation of the third driven roller 59 is stopped. However, in the fixing unit 16, when the print image is formed, the first belt 55 is heated to a desired temperature for forming the print image in a time as short as possible from the start of the heat generation of the heater 56. Those having a relatively small heat capacity are provided. Therefore, in the fixing unit 16, when the rotation of the first belt 55 is stopped while the heater 56 is generating heat, the first belt 55 may be locally heated by the heater 56 and damaged as the state is prolonged. Increase. In the fixing unit 16, when the temperature of the first belt 55 rises excessively, other parts in the fixing unit 16 are heated by the heat, and the possibility of damage increases. Therefore, when the control unit 48 detects that the rotation of the third driven roller 59 has stopped and a malfunction has occurred, the control unit 48 stops regardless of whether the rotation of the first belt 55 is actually stopped. When the occurrence of the malfunction is detected, the heating of the heater 56 is stopped. Accordingly, the control unit 48 can prevent the first belt 55 from being damaged while being continuously heated in a state where the rotation is stopped. Further, when the rotation of the third driven roller 59 stops, the control unit 48 also stops the operation of the unit drive motor 65, for example, the surface of the drive roller 53 with respect to the belt inner surface of the first belt 55 whose rotation has stopped. The unit drive motor 65 is prevented from being excessively loaded in an attempt to rotate the drive roller 53. In this manner, the control unit 48 prevents not only the first belt 55 but also the driving roller 53 and the unit driving motor 65 from being damaged.

  Further, in the fixing unit 16, when an operation failure occurs in which the rotation speeds of the first belt 55 and the second belt 60 are reduced (that is, changed), the medium conveyance speed in the sandwiching unit 61 is reduced below a specified amount. The amount of heat applied to the toner image on the medium 2 by the sandwiching unit 61 is larger than specified. For example, melted toner images may be mixed and color blur may occur in the printed image. For this reason, when the controller 48 detects that the rotation speed of the third driven roller 59 has changed and an operation failure has occurred, for example, the controller 48 controls the unit drive motor 65 to make the rotation speed of the drive roller 53 faster than specified. By doing so, the medium conveyance speed in the clamping part 61 is returned to the prescribed medium conveyance speed. As a result, the control unit 48 suppresses the change in the amount of heat applied to the toner image on the medium 2 in the sandwiching unit 61 as much as possible, and avoids the occurrence of color bleeding in the printed image formed on the surface of the medium 2 as much as possible. ing.

  Actually, in the fixing unit 16, the cycle in which the signal level of the rotation detection signal changes when the third driven roller 59 is rotating normally can be appropriately selected according to the number of blades of the rotating body 70. Specifically, in the fixing unit 16, for example, when the A2 size medium 2 is transported by vertical feeding with one short side directed in the transport direction, the printing speed per unit time for the medium 2 is 8 [ppm. ], The medium conveying speed TV by the first belt 55 and the second belt 60 is 53 [mm / s], the outer diameter OD of the third driven roller 59 is φ15, and the outer circumference OL of the third driven roller 59 is ( 1) Formula

OL = 15 [mm] × 3.14
= 47.1 [mm] (1)

The rotation speed RV of the third driven roller 59 per unit time (1 second) is expressed by the following equation (2).

RV = TV ÷ OL
= 53 [mm / s] ÷ 47.1 [mm]
≒ 1.125 [rps] (2)

It can be calculated as In the fixing unit 16, when the number N of blades of the rotating body 70 is four, the cycle T in which the signal level of the rotation detection signal changes is expressed by the following equation (3).

T = RV ÷ N
= 1.125 [rps] ÷ 4 [sheets]
≒ 0.28 [sec] (3)

It can be calculated as Since the response speed of the photosensor 71 of the photosensor 71 is generally about 0.01 seconds, the signal level of the rotation detection signal can be accurately changed according to the rotation of the third driven roller 59. Incidentally, in the fixing unit 16, when it is desired to make the cycle of changing the signal level of the rotation detection signal shorter than 0.28 seconds, the number of blades of the rotating body 70 may be increased more than four. When it is desired to make the cycle longer than 0.28 seconds, the number of blades of the rotating body 70 may be reduced from four.

  In the conventional image forming apparatus, a thermistor is used to detect the temperature of the core part of the fixing roller. Generally, the response speed of a temperature sensor such as a thermistor is about 2 seconds. For this reason, in the conventional image forming apparatus, even if it is detected that the medium conveyance speed has changed based on the detection result of the temperature of the cored bar by the thermistor and the drive motor is controlled, the medium conveyance speed actually changes. Therefore, it takes about 2 seconds at maximum to detect this and control the drive motor, and during that time, the medium 2 is transported at a medium transport speed different from the standard. On the other hand, in the color printer 1 according to the present embodiment, the rotation detecting unit 72 including the rotating body 70 and the photosensor 71 having a fast response speed is used for detecting the rotation of the third driven roller 59. When the medium conveyance speed at 61 is lower than the standard, it is possible to detect a decrease in the medium conveyance speed at a time point that is markedly earlier than the time when the medium conveyance speed is reduced as compared with the case where the temperature sensor is used. . Since the color printer 1 controls the unit drive motor 65 to restore the medium conveyance speed, the amount of heat applied to the toner image on the medium 2 in the clamping unit 61 is increased as compared with the case where the temperature sensor is used. As much as possible, it is possible to more reliably avoid the occurrence of color bleeding in the printed image formed on the surface of the medium 2. Further, in the color printer 1, even when the rotation of the first belt 55 heated by the heater 56 is stopped, the stop of the rotation can be detected at a much earlier time from the stop of the rotation. In the color printer 1, since the heat generation of the heater 56 is stopped when the rotation is detected, damage due to excessive heating of the first belt 55 can be avoided more reliably.

(1-3) Operation and Effect of Embodiment In the above configuration, in the color printer 1, the fixing unit 16 hangs the first belt 55 for heating the medium 2 on the driving roller 53 and the first driven roller 54. The second driven roller 58 and the third driven roller 59 are provided with a second belt 60 for pressurizing the medium 2, and the second driven roller 58 and the third driven roller 59 are connected to the second belt 60 and the first belt. 55 is sequentially pressed against the driving roller 53 and the first driven roller 54 to form a sandwiching portion 61 that heats and pressurizes the medium 2 while being conveyed by the first belt 55 and the second belt 60. In the color printer 1, the unit driving motor 65 is connected to the driving roller 53 of the fixing unit 16, so that the rotational driving force F 1 generated by the unit driving motor 65 is transmitted from the driving roller 53 to the first belt 55 and the first follower. Transmission is sequentially performed to the roller 54, and transmission is transmitted from the driving roller 53 to the second driven roller 58 and the third driven roller 59 via the first belt 55 and the second belt 60 sequentially. In addition, in the color printer 1, the fixing unit 16 is provided with a rotation detection unit 72 for detecting the rotation of the third driven roller 59 located on the downstream side of the driving force transmission path. When the color printer 1 forms the print image, the rotation of the third driven roller 59 in the fixing unit 16 stops unintentionally, and when the rotation speed changes, the control unit 48 causes the rotation detection unit 72 to execute the third detection. A stop of rotation of the driven roller 59 and a change in the rotation speed were detected. According to the configuration described above, the color printer 1 has a malfunction in which the rotation of the second belt 60 together with the first belt 55 stops in the fixing unit 16 when the print image is formed, Even if any of the operation failure in which the rotation of the two belts 60 stops and the operation failure in which the medium conveyance speed at the sandwiching portion 61 decreases, the occurrence of these various operation failures is detected from the drive roller 53 by the rotational driving force F1. This can be detected as a stop of rotation of the third driven roller 59 that has been rotated by the transmission of the rotation or a change in the rotation speed. As a result, the color printer 1 can easily detect the occurrence of various malfunctions in the fixing unit 16.

  In the color printer 1, the heater 56 is provided inside the first belt 55 in the fixing unit 16. In the color printer 1, the control unit 48 stops the rotation of the third driven roller 59 in the fixing unit 16, so that the first belt 55 and the second belt 60 stop rotating or the second belt 60 stops rotating. When it was detected that a malfunction occurred, the heat generation of the heater 56 was stopped. Accordingly, the color printer 1 can prevent the first belt 55 from being continuously heated and damaged in a state where the rotation is stopped in the fixing unit 16 when such a malfunction occurs. In addition to this, when the control unit 48 detects that the rotation of the third driven roller 59 has stopped in the fixing unit 16, the operation of the unit drive motor 65 is also stopped. Accordingly, in the color printer 1, the surface of the driving roller 53 is worn by rubbing against the inner surface of the first belt 55 whose rotation is stopped due to the occurrence of malfunction, and the driving roller 53 is rotated by the unit driving motor 65. It is possible to prevent an excessive load from being applied and to prevent damage to not only the first belt 55 but also the drive roller 53 and the unit drive motor 65. Furthermore, when the control unit 48 detects that a malfunction has occurred in the fixing unit 16 in which the medium conveyance speed in the clamping unit 61 is reduced as a change in the rotation speed of the third driven roller 59 in the fixing unit 16, The drive motor 65 was controlled so that the medium conveyance speed was restored. As a result, when such a malfunction occurs, the color printer 1 suppresses an increase in the amount of heat applied to the toner image on the medium 2 in the sandwiching unit 61 as much as possible, so that the color of the printed image formed on the surface of the medium 2 is reduced. It is possible to prevent bleeding.

  Further, in the color printer 1, the control unit 48 serves as the rotation detection unit 72 in the fixing unit 16 so as to rotate integrally with the third driven roller 59, and a photo arranged to face the rotation unit 70. The sensor 71 detects the stop of the rotation of the third driven roller 59 and the change in the rotation speed. Therefore, when an operation failure occurs in the fixing unit 16, the color printer 1 detects that the operation failure has occurred in the shortest possible time from the time of occurrence as a stop of rotation of the third driven roller 59 or a change in the rotation speed. be able to. Accordingly, when various malfunctions occur in the fixing unit 16, the color printer 1 can quickly cope with the malfunction, and damage due to excessive heating of the first belt 55, the driving roller 53 and the unit. It is possible to more reliably prevent damage to the drive motor 65, occurrence of color blur of the printed image on the medium 2, and the like.

(2) Other embodiments (2-1) Other embodiments 1
In the above-described embodiment, when it is detected that a malfunction has occurred in the fixing unit 16 in which the medium conveyance speed at the sandwiching portion 61 is reduced, the unit drive motor 65 is controlled based on the medium conveyance speed. The case where it was made to return was described. However, the present invention is not limited to this. For example, in the fixing unit 16, the pair of first bearing portions and the pair of third bearing portions, the pair of second bearing portions and the pair of fourth bearing portions are significantly deteriorated. For this reason, even if the unit drive motor 65 is controlled when the medium conveyance speed is reduced by the sandwiching unit 61, if the medium conveyance speed cannot be restored, the formation of the print image may be stopped. Here, in the fixing unit 16, a malfunction in which the medium conveyance speed decreases occurs when the medium 2 is sandwiched between the first driven roller 54 and the third driven roller 59 in the sandwiching unit 61, and driving This may occur when the medium 2 is sandwiched between the roller 53 and the second driven roller 58. In the present invention, the occurrence of such a malfunction is detected based on the rotation of the third driven roller 59 located upstream in the medium transport direction. Therefore, according to the present invention, when a malfunction occurs in which the medium conveyance speed decreases when the medium 2 is sandwiched between the first driven roller 54 and the third driven roller 59 in the sandwiching portion 61 of the fixing unit 16, the malfunction is caused. It is possible to immediately detect the occurrence of this and stop the formation of the printed image. Accordingly, in the present invention, for example, when a print image is continuously formed on a plurality of media 2 (that is, continuous printing), a print image in which color bleeding occurs on the plurality of media 2 is formed wastefully. This can be avoided as much as possible.

(2-2) Other embodiment 2
In the embodiment described above, the first belt 55 is hung on the driving roller 53 and the first driven roller 54 in the fixing unit 16, and the second belt 60 is hung on the second driven roller 58 and the third driven roller 59. The second driven roller 58 and the third driven roller 59 are pressed against the driving roller 53 and the first driven roller 54 with a predetermined pressing force through the first belt 55 and the second belt 60 in order, and the rotation detecting unit 72 is used. The case where the rotation of the third driven roller 59 is detected has been described. However, the present invention is not limited to this. For example, the rotation unit 70 may be provided on the second driven roller 58 in the fixing unit 16 and the rotation of the second driven roller 58 may be detected via the rotation detection unit 72. . Further, according to the present invention, for example, as shown in FIG. 9, the first belt 83 is stretched around the driving roller 81 and the first driven roller 82 in the fixing unit 80 (that is, the tension is applied), and the second driven The roller 84 is pressed against the driving roller 81 through the first belt 83 with a predetermined pressing force, and the sandwiched portion 85 is formed by the second driven roller 84 and the first belt 83. In the present invention, the heater 86 may be disposed inside the first belt 83 and the rotation of the second driven roller 84 may be detected via the rotation detector 72 (not shown). Further, according to the present invention, as shown in FIG. 10 in which the same reference numerals are given to corresponding parts to FIG. 9, a plate-shaped heater 91 having a resistance heating element is held in the fixing unit 90 in place of the first driven roller 82. A heater holding portion 92 may be provided, and the first belt 83 may be stretched around the driving roller 81 together with the heater holding portion 92. Furthermore, according to the present invention, for example, as shown in FIG. 11, the first belt 98 is stretched around the driving roller 96 and the first driven roller 97 in the fixing unit 95 and the second driven roller 99 is attached to the first belt 98. By pressing with a predetermined pressing force, the sandwiched portion 100 is formed by the second driven roller 99 and the first belt 98. In the present invention, the heater 101 may be disposed inside the first belt 98 and the rotation of the second driven roller 99 may be detected via the rotation detector 72 (not shown). In the present invention, the various configurations of the fixing units 16, 80, 90, and 95 are similar to those in the above-described embodiment based on the rotation of the second driven rollers 58, 84, and 99. It is possible to detect that a malfunction has occurred in the fixing units 16, 80, 90, 95.

(2-3) Other Embodiment 3
Further, in the above-described embodiment, the case where the fixing device according to the present invention is applied to the fixing units 16, 80, 90, and 95 provided in the color printer 1 described above with reference to FIGS. . However, the present invention is not limited to this, and a secondary transfer type color printer, a direct transfer method, a monochrome electrophotographic printer (hereinafter also referred to as a monochrome printer), an MFP (Multi-Function Peripheral), a facsimile, and a multifunction peripheral. The present invention can be widely applied to fixing devices having various other configurations, such as a fixing unit provided in an image forming apparatus such as a copying machine, and a fixing unit in which a heater is also disposed in the second belt 60.

(2-4) Other Embodiment 4
Further, in the above-described embodiment, the case where the image forming apparatus according to the present invention is applied to the color printer 1 described above with reference to FIGS. 1 to 11 has been described. However, the present invention is not limited to this, and can be widely applied to image forming apparatuses having various configurations such as a secondary transfer type color printer, a monochrome printer, an MFP, a facsimile, a multifunction peripheral, and a copying machine. it can.

(2-5) Other Embodiment 5
Further, in the above-described embodiment, a case where the rotation detection unit 72 including the rotating body 70 and the photosensor 71 described above with reference to FIGS. 1 to 11 is applied as the rotation detection unit that detects the rotation of the driven roller. Stated. However, the present invention is not limited to this, and a rotating body in which one slit is formed in the outer peripheral portion of the circular surface subjected to mirror finishing, or a plurality of slits are formed at predetermined intervals along the outer peripheral direction. , A rotation detection unit composed of a photo sensor, or one groove parallel to the longitudinal direction of the shaft is formed on the outer peripheral surface of the roller shaft, or a plurality of grooves parallel to the longitudinal direction of the shaft are formed at predetermined intervals along the circumferential direction. A rotation detection unit comprising: a formed driven roller; and a photosensor that irradiates the roller shaft of the driven roller with rotation detection light and receives reflected light obtained by reflecting the rotation detection light with one or a plurality of grooves. As described above, rotation detection units having various configurations can be widely applied.

  The present invention can be used for an image forming apparatus such as a color printer, a monochrome printer, an MFP, a facsimile machine, a multifunction peripheral, and a copying machine, and a fixing device provided in the image forming apparatus.

  DESCRIPTION OF SYMBOLS 1 ... Color printer, 2 ... Medium, 16, 80, 90, 95 ... Fixing unit, 50 ... Heating part, 51 ... Pressure part, 53, 81, 96 ... Driving roller, 54, 82, 97 …… first driven roller, 55, 83, 98 …… first belt, 56, 91 …… heater, 58, 84, 99 …… second driven roller, 59 …… third driven roller, 60 …… first 2 belts, 65... Unit drive motor, 70 rotating body, 71... Photo sensor, 72.

Claims (8)

An endless belt for conveying the medium;
A driving roller on which the belt is laid to rotate the belt;
A driven roller that rotates with the belt by transmitting a rotational driving force from the driving roller through the belt by being pressed against the belt;
A fixing device comprising: a rotation detection unit that detects rotation of the driven roller. The fixing device according to claim 1, further comprising a heater that is disposed inside the belt and heats the belt. Including another belt for transporting the medium together with the belt;
The driven roller is
The fixing device according to claim 1, wherein the other belt is laid and pressed against the belt via the other belt. A first driven roller on which the belt is hung together with the driving roller;
A second driven roller and a third driven roller as the driven roller on which the other belt is laid,
The second driven roller is
Pressed against the drive roller through the other belt and the belt sequentially,
The third driven roller is
Pressed against the first driven roller sequentially through the other belt and the belt,
The rotation detector
The fixing device according to claim 3, wherein rotation of one of the second driven roller and the third driven roller as the driven roller is detected. The first driven roller and the third driven roller are:
Arranged upstream of the drive roller and the second driven roller in the medium conveying direction,
The rotation detector
The fixing device according to claim 4, wherein rotation of the third driven roller located upstream in the medium conveyance direction is detected. The rotation detector
A rotating body that rotates integrally with the driven roller;
The fixing device according to claim 1, further comprising a photosensor disposed to face the surface of the rotating body. The heater is
The fixing device according to claim 2, wherein the fixing device is a halogen lamp. The image forming apparatus according to claim 1, further comprising the fixing device.

Images