JP6187224B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an electrophotographic image forming apparatus including a fixing device.

  In general, in an image forming apparatus (printer, copying machine, facsimile, etc.) using an electrophotographic process technology, a laser beam based on image data is irradiated (exposed) to a uniformly charged photoconductor (for example, a photoconductive drum). ), An electrostatic latent image is formed on the surface of the photoreceptor. Then, toner is supplied to the photoconductor on which the electrostatic latent image is formed, so that the electrostatic latent image is visualized and a toner image is formed. The toner image is transferred directly or indirectly to the sheet via an intermediate transfer member, and then heated and pressed by a fixing device, whereby an image is formed on the sheet.

  The fixing device is disposed on an upper fixing portion having a fixing surface side member disposed on an image forming surface (surface on which a toner image is formed) side of a sheet, and on a back surface (surface opposite to the fixing surface) side of the sheet. A lower fixing unit having a back side support member, a heating source, and the like are provided. By pressing the back side support member against the fixing side member, a fixing nip for nipping and transporting the paper is formed.

  In recent years, a wax-containing toner (also referred to as an oilless toner) in which a large amount of wax is contained in toner particles has been developed. In the case of using a wax-containing toner, the wax that exudes to the toner surface at the time of fixing acts as a release material, thereby ensuring the releasability between the sheet and the fixing surface side member. However, when the wax exuded from the toner adheres to the fixing surface side member, the wax is transferred to the next sheet, and there is a possibility that uneven glossiness occurs in the image.

The present applicant has developed a technique for preventing uneven glossiness by making the peripheral speed (surface speed) of the fixing surface side member slower than the peripheral speed of the back surface side support member and slipping the fixing surface side member on the paper. is suggesting. Specifically, by rotating the fixing surface side member following the rotation of the back surface side support member, and generating torque (braking force) in a direction to brake the rotation of the fixing surface side member by the torque generating unit, The fixing surface side member is slipped. The torque generator includes a first motor (brake motor) that generates torque in a direction to brake rotation of the fixing surface side member, and a second motor (assist motor) that generates torque in the rotation direction of the fixing surface side member. Can be used to control the generated torque. Hereinafter, the direction in which the rotation of the fixing surface side member is braked is referred to as “brake direction”, the reverse direction is referred to as “assist direction”, the brake direction torque is referred to as “brake force”, and the assist direction torque is referred to as “assist force”.
As a technique for controlling the torque generated in the rotating body, for example, Patent Document 1 is available. In patent document 1, the brake means comprised with the electrorheological fluid is controlled according to the load fluctuation which arises in a rotary body.

JP 2006-58758 A

  In the torque generator described above, if an operation abnormality occurs in the first motor or the second motor, an appropriate braking force is not generated, and as a result, the fixing surface side member does not slip properly and uneven gloss occurs. Can not be prevented. Therefore, a means for detecting an abnormality in the torque generating unit is required. Usually, abnormal operation of the motor can be determined by whether or not the motor is rotating. However, the first motor and the second motor used in the torque generating unit rotate the back side support member during image formation. Therefore, it is impossible to detect an abnormal operation based on the rotation of the motor.

  An object of the present invention is to provide an image forming apparatus capable of detecting an abnormal operation of a torque generating unit during image formation and forming a high-quality image without uneven gloss.

An image forming apparatus according to the present invention includes a fixing surface side member disposed on a fixing surface side of a sheet on which a toner image is formed,
A back-side support member that is disposed on the back side of the sheet and forms a fixing nip that sandwiches and conveys the sheet by being pressed against the fixing-side member;
A drive unit for rotating the back side support member at a predetermined peripheral speed,
An image forming apparatus for fixing a toner image on a sheet passing through the fixing nip by rotating the back surface side support member in a state of being pressed against the fixing surface side member and rotating the fixing surface side member. Because
A torque generating unit that applies a braking force in a direction that prevents rotation to the fixing surface side member;
A braking force control unit that controls the torque generation unit so that a predetermined torque is generated in the back side support member;
And an operation abnormality detection unit that detects an operation abnormality of the torque generation unit based on a drive current supplied to the drive unit during paper feeding.

  According to the present invention, since the operation abnormality of the torque generating unit is detected based on the driving current supplied to the driving unit for the back surface side support member rather than the rotation state of the motor constituting the torque generating unit, the torque generating unit It is possible to reliably detect an abnormal operation. Therefore, it is possible to reliably prevent uneven glossiness from occurring due to abnormal operation of the torque generating portion, and to form a high-quality image.

1 is a diagram illustrating an overall configuration of an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a diagram illustrating a main part of a control system of the image forming apparatus according to the embodiment. FIG. 3 is a diagram illustrating an example of a fixing unit. It is a figure which shows the braking force provided to a fixing roller by a torque generation part. It is a flowchart which shows an example of the operation abnormality detection process which concerns on embodiment. It is a flowchart which shows an example of the operation | movement abnormality detection process which concerns on a modification.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a diagram showing an overall configuration of an image forming apparatus 1 according to an embodiment of the present invention. FIG. 2 is a diagram illustrating a main part of a control system of the image forming apparatus 1 according to the embodiment.
An image forming apparatus 1 shown in FIGS. 1 and 2 is an intermediate transfer type color image forming apparatus using electrophotographic process technology. In the image forming apparatus 1, photosensitive drums 413 corresponding to four colors of CMYK are arranged in series in the running direction (vertical direction) of the intermediate transfer belt 421, and each color toner image is sequentially transferred to the intermediate transfer belt 421 in one procedure. The vertical tandem system is adopted.
That is, the image forming apparatus 1 primarily transfers Y (yellow), M (magenta), C (cyan), and K (black) color toner images formed on the photosensitive drum 413 to the intermediate transfer belt 421, After the four color toner images are superimposed on the transfer belt 421, the image is formed by secondary transfer onto the paper.

  As shown in FIGS. 1 and 2, the image forming apparatus 1 includes an image reading unit 10, an operation display unit 20, an image processing unit 30, an image forming unit 40, a paper transport unit 50, a fixing unit 60, and a control unit 100. .

  The control unit 100 includes a CPU (Central Processing Unit) 101, a ROM (Read Only Memory) 102, a RAM (Random Access Memory) 103, and the like. The CPU 101 reads out a program corresponding to the processing content from the ROM 102 or the storage unit 72, develops it in the RAM 103, and centrally controls the operation of each block of the image forming apparatus 1 in cooperation with the developed program.

  The storage unit 72 includes, for example, a nonvolatile semiconductor memory (so-called flash memory) or a hard disk drive. The storage unit 72 stores a lookup table LUT that is referred to when, for example, controlling the operation of each block.

  The control unit 100 also exchanges various data with an external device (for example, a personal computer) connected to a communication network such as a LAN (Local Area Network) or a WAN (Wide Area Network) via the communication unit 71. Send and receive. For example, the control unit 100 receives image data (input image data) in a page description language (PDL) transmitted from an external device, and forms an image on a sheet based on the received image data. The communication unit 71 has various interfaces such as a network interface card (NIC), a modem-demodulator (MODEM), and a universal serial bus (USB).

The image reading unit 10 includes an automatic document feeder 11 called an ADF (Auto Document Feeder), a document image scanning device 12 (scanner), and the like.
The automatic document feeder 11 conveys the document placed on the document tray by the conveyance mechanism and sends it out to the document image scanning device 12. The automatic document feeder 11 can continuously read images (including both sides) of a large number of documents placed on the document tray.
The document image scanning device 12 optically scans a document conveyed on the contact glass from the automatic document feeder 11 or a document placed on the contact glass, and reflects light from the document to a CCD (Charge Coupled Device). ) An image is formed on the light receiving surface of the sensor 12a, and an original image is read. The image reading unit 10 generates input image data based on the reading result by the document image scanning device 12. The input image data is subjected to predetermined image processing in the image processing unit 30.

The operation display unit 20 is configured by, for example, a liquid crystal display (LCD) with a touch panel, and functions as a display unit 21 and an operation unit 22. The display unit 21 displays various operation screens, an image status display, an operation status of each function, and the like in accordance with a display control signal input from the control unit 100. The operation unit 22 includes various operation keys such as a numeric keypad and a start key, receives various input operations by the user, and outputs an operation signal to the control unit 100.
The user can operate the operation display unit 20 to perform settings relating to image formation such as document setting, image quality setting, magnification setting, application setting, output setting, single-sided / double-sided setting, paper setting, and swing amount adjustment. .

  The image processing unit 30 includes a circuit that performs digital image processing on input image data according to initial settings or user settings. For example, the image processing unit 30 performs tone correction based on tone correction data (tone correction table) under the control of the control unit 100 (image density control). Further, the image processing unit 30 performs various correction processes such as color correction and shading correction, compression process, and the like on the input image data. The image forming unit 40 is controlled based on the image data subjected to these processes.

  The image forming unit 40 includes an image forming unit 41 and an intermediate transfer unit 42 for forming an image using colored toners of Y component, M component, C component, and K component based on input image data.

  The image forming unit 41 includes four image forming units 41Y, 41M, 41C, and 41K for Y component, M component, C component, and K component. Since the image forming units 41Y, 41M, 41C, and 41K have the same configuration, for convenience of illustration and description, common constituent elements are denoted by the same reference numerals, and when distinguished from each other, the reference numerals Y, M, and C are used. Or K. In FIG. 1, reference numerals are given only to the components of the image forming unit 41Y for the Y component, and reference numerals of the constituent elements of the other image forming units 41M, 41C, 41K are omitted.

  The image forming unit 41 includes an exposure device 411, a developing device 412, a photosensitive drum 413, a charging device 414, a drum cleaning device 415, and the like.

The photosensitive drum 413 includes, for example, an undercoat layer (UCL), a charge generation layer (CGL), and a charge transport layer (CTL) on the peripheral surface of an aluminum conductive cylinder (aluminum tube). : A negatively charged organic photoconductor (OPC) in which Charge Transport Layers are sequentially stacked.
The charge generation layer is made of an organic semiconductor in which a charge generation material (for example, phthalocyanine pigment) is dispersed in a resin binder (for example, polycarbonate), and generates a pair of positive charges and negative charges upon exposure by the exposure device 411. The charge transport layer consists of a hole transport material (electron donating nitrogen-containing compound) dispersed in a resin binder (for example, polycarbonate resin), and transports positive charges generated in the charge generation layer to the surface of the charge transport layer. To do.

  The charging device 414 is constituted by a corona discharge generator such as a scorotron charging device or a corotron charging device. The charging device 414 uniformly charges the surface of the photosensitive drum 413 to a negative polarity by corona discharge.

  The exposure apparatus 411 is composed of, for example, a semiconductor laser. The exposure device 411 irradiates the photosensitive drum 413 with laser light corresponding to the image of each color component. The positive charge generated in the charge generation layer of the photosensitive drum 413 is transported to the surface of the charge transport layer, so that the surface charge (negative charge) of the photosensitive drum 413 is neutralized. Thereby, an electrostatic latent image of each color component is formed on the surface of the photosensitive drum 413 due to a potential difference from the surroundings.

  The developing device 412 accommodates developer of each color component (two-component developer composed of toner and magnetic carrier), and visualizes the electrostatic latent image by attaching the toner of each color component to the surface of the photosensitive drum 413. Thus, a toner image is formed. Specifically, a developing bias voltage is applied to the developer carrying member (developing roller), and the charged toner on the developer carrying member is applied to the surface of the photosensitive drum 413 by the potential difference between the surface of the photosensitive drum 413 and the developer carrying member. Move to and adhere to exposed areas.

  Here, as the toner contained in the developing device 412, a wax-containing toner in which a large amount of wax is contained in the toner particles is used. The melting point of the wax contained in this toner is usually as low as 110 ° C. or less. Examples of the wax include known waxes such as paraffin wax, polyolefin wax, modified products thereof (for example, oxides and graphs and processed products), higher fatty acids, and metal salts thereof, amide waxes, ester waxes, and the like. Applicable. In particular, higher fatty acid ester waxes are suitable.

  The drum cleaning device 415 includes a drum cleaning blade that is in sliding contact with the surface of the photosensitive drum 413, and removes transfer residual toner remaining on the surface of the photosensitive drum 413 after primary transfer.

  The intermediate transfer unit 42 includes an intermediate transfer belt 421, a primary transfer roller 422, a plurality of support rollers 423, a secondary transfer roller 424, a belt cleaning device 426, and the like.

  The intermediate transfer belt 421 is an endless belt, and is stretched around a plurality of support rollers 423 in a loop shape. At least one of the plurality of support rollers 423 is configured by a driving roller, and the other is configured by a driven roller. For example, the support roller 423A disposed on the downstream side in the belt traveling direction from the primary transfer roller 422 for the K component is preferably a drive roller (hereinafter referred to as “drive roller 423A”). This makes it easy to keep the belt running speed constant in the primary transfer portion. As the driving roller 423A rotates, the intermediate transfer belt 421 travels in the direction of arrow A at a constant speed.

  The primary transfer roller 422 is disposed on the inner peripheral surface side of the intermediate transfer belt 421 so as to face the photosensitive drum 413 of each color component. The primary transfer roller 422 is pressed against the photosensitive drum 413 with the intermediate transfer belt 421 interposed therebetween, whereby a primary transfer nip for transferring a toner image from the photosensitive drum 413 to the intermediate transfer belt 421 is formed.

  The secondary transfer roller 424 is disposed on the outer peripheral surface side of the intermediate transfer belt 421 so as to face a support roller 423B (hereinafter referred to as “backup roller 423B”) disposed on the downstream side in the belt traveling direction of the drive roller 423A. The secondary transfer roller 424 is pressed against the backup roller 423B with the intermediate transfer belt 421 interposed therebetween, thereby forming a secondary transfer nip for transferring the toner image from the intermediate transfer belt 421 to the sheet.

  When the intermediate transfer belt 421 passes through the primary transfer nip, the toner images on the photosensitive drum 413 are primarily transferred to the intermediate transfer belt 421 in order. Specifically, a primary transfer bias is applied to the primary transfer roller 422, and an electric charge having a polarity opposite to that of the toner is applied to the back side of the intermediate transfer belt 421 (the side in contact with the primary transfer roller 422). It is electrostatically transferred to the intermediate transfer belt 421.

  Thereafter, when the sheet passes through the secondary transfer nip, the toner image on the intermediate transfer belt 421 is secondarily transferred to the sheet. Specifically, by applying a secondary transfer bias to the secondary transfer roller 424 and applying a charge having a polarity opposite to that of the toner to the back side of the paper (the side in contact with the secondary transfer roller 424), the toner image becomes It is electrostatically transferred to the paper. The sheet on which the toner image has been transferred is conveyed toward the fixing unit 60.

  The belt cleaning device 426 includes a belt cleaning blade that is in sliding contact with the surface of the intermediate transfer belt 421 and removes transfer residual toner remaining on the surface of the intermediate transfer belt 421 after the secondary transfer.

  In the intermediate transfer unit 42, instead of the secondary transfer roller 424, a secondary transfer belt is looped around a plurality of support rollers including the secondary transfer roller (so-called belt-type secondary transfer). Unit) may be adopted.

  The fixing unit 60 is disposed on the upper fixing unit 61 having a fixing surface side member disposed on the fixing surface (surface on which the toner image is formed) side of the paper, and on the back surface (surface opposite to the fixing surface) side of the paper. A lower fixing unit 62 having a back surface side support member, a heating source 63 for heating the fixing surface side member, and the like.

  When the upper fixing unit 61 is a belt heating method (see FIG. 2), the fixing belt is a fixing surface side member, and when it is a roller heating method, the fixing roller is a fixing surface side member. Further, when the lower fixing unit 62 is a roller pressurization method (see FIG. 2), the pressure roller is a back surface side support member, and when the lower fixing unit 62 is a belt pressure method, the pressure belt is a back surface side support member. When the back surface side support member is pressed against the fixing surface side member, a fixing nip for nipping and transporting the sheet is formed. The sheet onto which the toner image has been secondarily transferred and conveyed is heated and pressurized when passing through the fixing nip. As a result, the toner image is fixed on the paper. Further, the fixing unit 60 may include a separation air blowing unit that blows air to the fixing surface side member or the back surface side support member and separates the sheet from the fixing surface side member or the back surface side support member. Details of the fixing unit 60 will be described later.

The paper transport unit 50 includes a paper feed unit 51, a paper discharge unit 52, a first transport unit 53, a second transport unit 54, and the like.
In the three paper feed tray units 511 to 513 constituting the paper feed unit 51, paper (standard paper, special paper) identified based on basis weight, size, etc. is stored for each preset paper type. .

  The first transport unit 53 includes a plurality of transport roller units including an intermediate transport roller unit 531, a loop roller unit 532, and a registration roller unit 533. The first transport unit 53 transports paper fed from the paper feed unit 51 or an external paper feed device (not shown) to the image forming unit 40 (secondary transfer unit).

  The 2nd conveyance part 54 is provided with the switchback path | route 541 and the conveyance path 542 for back surfaces by which the some conveyance roller part is arrange | positioned. The second transport unit 54 once transports the paper to the switchback path 541, switches back and transports the paper to the back-side transport path 542, thereby reversing the paper, and the first transport unit 53 (loop roller unit 532). Upstream).

  A sheet fed from the sheet feeding unit 51 or an external sheet feeding device (not shown) is conveyed to the image forming unit 40 by the first conveying unit 53. Then, when the sheet passes through the secondary transfer nip, the toner image on the intermediate transfer belt 421 is secondarily transferred to one side (fixing surface) of the sheet at once and subjected to a fixing process in the fixing unit 60. . The paper on which the image is formed is discharged out of the apparatus by a paper discharge unit 52 having a paper discharge roller 52a. When images are formed on both sides of the paper, the paper on which the image is formed on the front surface is sent to the second transport unit 54, and after being inverted, an image is formed on the back surface.

  Hereinafter, the configuration of the fixing unit 60 will be described in detail. FIG. 3 is a diagram illustrating an example of the fixing unit 60. 3 includes a belt heating type upper fixing unit 61, a roller pressing type lower fixing unit 62, a heating source 63, a torque generating unit 64, and the like.

  The upper fixing unit 61 includes a fixing roller 611, a heating roller 612, a support roller 613, and an endless fixing belt 614 stretched around these. Here, a heating source 63 such as a halogen lamp is built in the heating roller 612. The heating source 63 may be an electromagnetic induction heating type.

The fixing roller 611 has a configuration in which an elastic layer made of silicone rubber or the like is formed on the outer peripheral surface of a columnar core made of iron or the like. A surface release layer made of a fluororesin may be formed on the outer peripheral surface of the elastic layer.
A torque generator 64 for braking the rotation of the fixing roller 611 is connected to the fixing roller 611. The torque generator 64 includes a power transmission mechanism (gear mechanism) 641 that individually transmits the power of the first motor M1, the second motor M2, the first motor M1, and the second motor M2 to the fixing roller 611. . Drive control of the first motor M1 and the second motor M2 is performed by the control unit 100.

  The fixing belt 614 has a configuration in which, for example, an elastic layer made of silicone rubber and a surface release layer made of a fluorine-based resin are sequentially laminated on a film base made of heat-resistant polyimide. As the fluorine-based resin, a material containing any of PFA (perfluoroalkoxyalkane), PTFE (polytetrafluoroethylene), and FEP (hexafluoropropylene copolymer) can be applied. As a result, the surface releasability of the fixing belt 614 with respect to the wax contained in the toner resin or toner particles is improved, and the toner is easily separated from the surface of the fixing belt 614 during fixing.

The lower fixing unit 62 includes a pressure roller 621 serving as a back side support member. The pressure roller 621 has the same configuration as the fixing roller 611.
A pressure contact / separation portion 65 (see FIG. 2) is connected to the pressure roller 621 through a power transmission mechanism (not shown). The pressing / separating unit 65 includes a biasing unit (not shown) that biases the pressure roller 621 against the fixing roller 611, and determines the state of the pressure roller 621 with respect to the fixing belt 614 (fixing surface side member). Switch to state or separated state.
The pressure roller 621 is connected to a drive motor M3 for rotationally driving the pressure roller 621. Drive control of the press contact / separation unit 65 and drive control of the drive motor M3 are performed by the control unit 100. The drive current of the drive motor M3 is controlled so that the peripheral speed of the pressure roller 621 is constant.

  The lower fixing unit 62 may include a heating source for heating the pressure roller 621 in order to suppress a temperature drop of the fixing belt 614 during pressing (to suppress heat radiation from the fixing belt 614). Good. Further, since the image quality deteriorates when the temperature of the pressure roller 621 becomes too high, a lower cooling unit (for example, a cooling fan) for cooling the pressure roller 621 may be provided.

  The pressure roller 621 is pressed against the fixing roller 611 via the fixing belt 614 by the press contact / separation unit 65. Thereby, a fixing nip for nipping and conveying the sheet is formed. The sheet onto which the toner image has been secondarily transferred and conveyed is pressurized when passing through the fixing nip, and is heated at a fixing temperature (for example, 160 to 200 ° C.) while being in contact with the fixing belt 614. As a result, the toner image is fixed on the paper.

  Further, the fixing roller 611 rotates following the rotation of the pressure roller 621 together with the fixing belt 614. That is, when the torque generator 64 does not operate, the peripheral speeds of the fixing roller 611, the fixing belt 614, and the pressure roller 621 are the same. In the present embodiment, the torque generator 64 generates a braking force in a direction that prevents the rotation of the fixing belt 614, so that the peripheral speed of the fixing belt 614 is slower than the peripheral speed of the pressure roller 621. Since the fixing belt 614 slips on the paper, it is possible to prevent uneven glossiness from occurring in the image.

  The operation of the torque generating unit 64 will be specifically described. The first motor M1 is in a non-powered state and stops normal driving, thereby functioning as a generator when the fixing roller 611 rotates. The first motor M1 applies a torque (brake force) F1 in the braking direction opposite to the rotation direction to the fixing roller 611 by rotational resistance when operating as a generator. On the other hand, the second motor M2 is driven by the control unit 100 and applies a torque (assist force) F2 in the assist direction in the same direction as the rotation direction to the fixing roller 611.

  Each of the first motor M1 and the second motor M2 outputs an operation signal indicating its own rotation state to the control unit 100. When the first motor M1 operates as a brake unit, normal driving is stopped, but the motor rotates by the rotation of the fixing roller 611 following the rotation of the pressure roller 621, so that the first motor M1 is in a rotating state. The operation signal shown is output.

  FIG. 4 is a diagram illustrating a braking force applied to the fixing roller 611 by the torque generator 64. As shown in FIG. 4, the braking force F1 applied by the first motor M1 is constant (-0.1 N · m in FIG. 4). The assist force F2 applied by the second motor M2 is variable by PWM (Pulse Width Modulation) control, and the magnitude thereof is controlled based on the torque generated in the pressure roller 621 (in FIG. 4). 0-0.08 N · m). Thus, the assist force F2 is a value within the range of the brake force F1 (that is, a value smaller than the absolute value of the brake force F1).

  A torque (= F1 + F2) obtained by adding the braking force F1 and the assist force becomes the braking force F acting on the fixing roller 611. Due to this braking force F, the peripheral speed of the fixing roller 611 (the peripheral speed of the fixing belt 614) becomes 0.3 to 0.8% slower than the peripheral speed of the pressure roller 621, and the fixing belt 614 moves on the sheet S. Slip.

  When the braking force F is applied to the fixing roller 611, a frictional force is generated between the fixing belt 614 and the pressure roller 621 due to the peripheral speed difference, and thus torque is generated in the pressure roller 621. In order to prevent the occurrence of uneven gloss, it is necessary to maintain the torque generated in the pressure roller 621 within a predetermined range and stabilize the slip amount.

Therefore, when the torque generated in the pressure roller 621 is larger than the target torque (hereinafter “target torque”), the control unit 100 controls the drive of the second motor so that the assist force F2 is increased. Do. Thereby, since the braking force F becomes small, the torque generated in the pressure roller 621 becomes small and approaches the target torque.
Conversely, when the torque generated in the pressure roller 621 is smaller than the target torque, the control unit 100 controls the driving of the second motor M2 so that the assist force F2 is reduced. As a result, the braking force F increases, so the torque generated in the pressure roller 621 increases and approaches the target torque.

  Since the drive current of the drive motor M3 is controlled so that the peripheral speed of the pressure roller 621 is constant, the torque generated in the pressure roller 621 can be detected based on this drive current. That is, when the drive current is large, the torque generated in the pressure roller 621 is large, and when the drive current is small, the torque generated in the pressure roller 621 is small. For example, by storing data indicating the correlation between the drive current to the drive motor M3 and the rotational torque of the drive motor M3 in the storage unit 72, the drive current supplied to the drive motor M3 is transferred to the pressure roller 621. The generated torque can be easily detected.

As described above, the image forming apparatus 1 is disposed on the fixing surface side of the sheet on which the toner image is formed, the fixing belt 614 (fixing surface side member), and disposed on the back side of the sheet, and is in pressure contact with the fixing belt 614. Thus, a pressure roller 621 (back side support member) that forms a fixing nip for nipping and conveying the paper, and a drive motor M3 (drive unit) for rotating the pressure roller 621 at a predetermined peripheral speed. And the pressure roller 621 rotates in a state of being pressed against the fixing belt 614, whereby the fixing belt 614 follows and rotates to fix the toner image on the sheet passing through the fixing nip.
In addition, the image forming apparatus 1 includes a torque generating unit 64 that applies a braking force in a direction that prevents rotation (braking direction) to the fixing belt 614, and a torque that generates a predetermined torque (target torque) in the pressure roller 621. And a control unit 100 (braking force control unit) that controls the generation unit 64.

  Specifically, the torque generation unit 64 operates as a brake unit that applies a braking force F1 (first torque) in a direction that prevents rotation to the fixing belt 614 (fixing surface side member). And a second motor M2 that operates as an assist unit that applies assist force F2 (second torque) in a direction that assists rotation to the fixing belt 614, and includes a control unit 100 (braking force control unit). ) Controls the braking force F by adjusting the assist force F2 by the second motor M2.

  The control unit 100 as a braking force control unit adjusts the braking force F1 by the first motor M1, or both the braking force F1 by the first motor M1 and the assisting force F2 by the second motor M2. The braking force F may be controlled by controlling.

  Further, in the present embodiment, the operation current of the torque generator 64, that is, the first motor M1 or the second motor M2 is detected using the drive current of the drive motor M3. Note that, by using the drive current of the drive motor M3, it is possible to detect an operation abnormality in the second motor M2 that operates as the assist unit, but here, the operation in the first motor M1 that operates as the brake unit. A case where an abnormality is detected will be described. This is because the first motor M1 generates heat due to the rotational resistance when operating as a generator, and therefore, abnormal operation is more likely to occur than the second motor M2.

FIG. 5 is a flowchart illustrating an example of the operation abnormality detection process according to the embodiment. The operation abnormality detection process shown in FIG. 5 is realized, for example, when the CPU 101 executes a predetermined program stored in the ROM 102 when image formation is started.
Here, when the difference between the drive current Ib (hereinafter referred to as “reference current Ib”) of the reference drive motor M3 and the actual drive current is larger than 2.0 A, the torque generator 64 (first It is assumed that the motor M1) operates abnormally. The initial value of the reference current Ib is set in advance. For example, when the drive current when the target torque is generated in the pressure roller 621 is 4.0 A, this is set as the initial value of the reference current Ib.

  As shown in FIG. 5, first, in step S <b> 101, the control unit 100 determines whether or not paper feeding to the fixing nip has been started. Then, when the control unit 100 determines that the sheet passing to the fixing nip has been started, the process proceeds to step S102.

  In step S102, the control unit 100 acquires the drive current supplied to the drive motor M3. The drive current increases as the torque generated in the pressure roller 621 increases. In the second motor M2, the assist force (first torque) is set so that the torque generated in the pressure roller 621 becomes the target torque, that is, the drive current supplied to the drive motor M3 is 4.0A. The driving current of the second motor M2 is controlled.

  In step S103, the control unit 100 determines whether or not the sheet passing through the fixing nip is completed. If the control unit 100 determines that the sheet passing through the fixing nip is completed, the process proceeds to step S104. On the other hand, when the control unit 100 determines that the sheet passing through the fixing nip is not completed, the process proceeds to step S102, and the drive current supplied to the drive motor M3 is reacquired. Since the assist force by the second motor M2 changes according to the drive current supplied to the drive motor M3, the re-acquired drive current also changes with time.

  Whether or not the sheet feeding to the fixing nip is started (step S101) and whether or not the sheet passing through the fixing nip is completed (step S103) depend on the time after the sheet passes through the registration roller portion 533. Judgment can be made. For example, the transport distance from the registration roller 533 to the fixing nip entrance is 300 mm, the fixing nip width (fixing nip entrance to exit) is 30 mm, the paper transport speed is 300 mm / sec, and A4 size paper (paper in the paper transport direction) When a length of 210 mm is used, the sheet feeding to the fixing nip is started 1 sec (= 300 [mm] / 300 [mm / sec]) after passing through the registration roller portion 533. Further, after passing through the registration roller portion 533, the paper passing through the fixing nip is completed after 1.8 sec (= (300 [mm] +30 [mm] +210 [mm]) / 300 [mm / sec]). Accordingly, a period of 1 to 1.8 sec after passing through the registration roller portion 533 is during the sheet passing, and during this period, the driving current supplied to the driving motor M3 is acquired at a predetermined interval (for example, an interval of 10 msec).

  In step S104, the control unit 100 calculates an average value Ia (hereinafter, “average current Ia”) of the drive current supplied to the drive motor M3.

  In step S105, the control unit 100 determines whether or not the difference between the reference current Ib (initial value: 4.0A) and the average current Ia is greater than 2.0A. If the controller 100 determines that the difference between the reference current Ib and the average current Ia is greater than 2.0 A, the process proceeds to step S108. On the other hand, if it is determined that the difference between the reference current Ib and the average current Ia is 2.0 A or less, the process proceeds to step S106.

  When the difference between the reference current Ib and the average current Ia is 2.0 A or less, the torque generator 64 is operating normally. In this case, in step S106, the control unit 100 sets the current average current Ia as the reference current Ib. Abnormal operation of the motor when the next sheet is passed is determined by comparison with a newly set reference current Ib.

  On the other hand, when the difference between the reference current Ib and the average current Ia is larger than 2.0 A, an excessive torque is generated in the pressure roller 621, and the torque generator 64 (first motor M1) operates normally. Will not be. In this case, in step S108, the control unit 100 stops the subsequent image forming process on the sheet. Note that the paper that is currently forming an image is discharged as it is.

  In this case, it is preferable to display on the display unit 21 that an operational abnormality has occurred in the torque generating unit 64 to notify the error and to prompt a repair work by a service person. Further, since the discharged paper includes an abnormal image, it is preferable to display this on the display unit 21.

  In step S107, the control unit 100 determines whether a series of image forming processes has been completed. A series of image forming processes is a process of forming an image for the number of sheets set by a signal (for example, a print job) instructing image formation. When the control unit 100 determines that the series of image forming processes has ended, the operation abnormality detection process ends. When the control unit 100 determines that the series of image forming processes has not ended, the processes after step S101 are performed. Is repeated.

  As described above, in the image forming apparatus 1, the control unit 100 serving as the operation abnormality detection unit is based on the average current Ia (the drive current supplied to the drive motor M <b> 3 (drive unit) when the paper is passed). Detect abnormal operation.

  Torque is generated because the abnormal operation of the torque generator 64 is detected based on the drive current supplied to the drive motor M3 rather than the rotational states of the first motor M1 and the second motor M2 constituting the torque generator 64. An operation abnormality in the unit 64 can be reliably detected. Therefore, it is possible to reliably prevent the occurrence of uneven glossiness due to the abnormal operation of the torque generating unit 64, and a high quality image can be formed.

[Modification]
Incidentally, the target torque in the pressure roller 621 is set according to the paper type. For this reason, when the paper type of the paper used for image formation is changed, if the paper type changing process is not performed appropriately, an operation error of the torque generating unit 64 may be erroneously detected.
That is, as described above, when the difference between the reference current Ib and the average current Ia is larger than 2.0 A (“YES” in step S105 in FIG. 5), an excessive torque is generated in the pressure roller 621. Although it can be determined that the torque generating unit 64 (first motor M1) is not operating normally, the paper type of the actually used paper differs from the set paper type due to a user setting error. There is also a possibility of false detection. For example, when the set paper is thick paper and the thin paper is passed, the torque generated in the pressure roller 621 becomes small (the average current Ia becomes small), and therefore the reference current Ib and the average current Ia The difference between the two becomes large, resulting in false detection.
Therefore, in the modified example, when an abnormal operation of the torque generating unit 64 is recognized (“YES” in step S205 in FIG. 6), the abnormal operation of the torque generating unit 64 is not stopped immediately, but the image formation is not stopped immediately. Processing for confirmation is performed (steps S208 to S213).

  FIG. 6 is a flowchart illustrating an example of the operation abnormality detection process according to the modification. The processing in steps S201 to S207 in FIG. 6 is the same as the processing in steps S101 to S107 in FIG.

  In step S208, the control unit 100 temporarily stops the subsequent image forming process on the sheet. Note that the paper that is currently forming an image is discharged as it is.

  In step S <b> 209, the control unit 100 stops driving the second motor M <b> 2 that has been operating as the assist unit, and operates the pressure contact / separation unit 65 to separate the pressure roller 621 from the fixing belt 614.

  In step S210, the control unit 100 starts power feeding to the first motor M1 that has been operating as the brake unit, and drives the first motor M1.

  In step S211, the control unit 100 determines whether or not the operation signal output from the first motor M1 is an abnormal signal indicating a non-rotating state. If the control unit 100 determines that the operation signal output from the first motor M1 is an abnormal signal, the process proceeds to step S213. On the other hand, when the control unit 100 determines that the operation signal output from the first motor M1 is not an abnormal signal, the process proceeds to step S212.

  If the operation signal output from the first motor M1 is not an abnormal signal (“NO” in step S211), the operation of the first motor M1 is normal, and therefore the control unit 100 has stopped in step S212. The image forming process resumed. However, it is considered that the paper type or the like has been set incorrectly due to a user setting error or the like, so that the fact is notified to the display unit 21 so that the image forming process is resumed after the incorrect setting is eliminated. Is preferable.

If the operation signal output from the first motor M1 is an abnormal signal (“YES” in step S211), the first motor M1 has actually failed, so in step S213, the control unit 100 Stops the image forming process. In this case, it is preferable to display on the display unit 21 that an operational abnormality has occurred in the torque generating unit 64 to notify the error and to prompt a repair work by a service person.
Regardless of whether or not the image forming process is restarted, the discharged paper includes an abnormal image. Therefore, it is preferable to display this on the display unit 21.

  As described above, in the image forming apparatus 1, when the control unit 100 as the operation abnormality detection unit detects an operation abnormality of the torque generation unit 64, the fixing belt 614 (fixing surface side member) and the pressure roller 621 (back surface). The first motor M1 is operated with the side support member in the separated state, and the abnormal operation of the torque generator 64 is determined based on the rotational state of the first motor M1.

  Thereby, since it can be confirmed whether or not the first motor M1 operating as a brake unit in the torque generating unit 64 is actually broken, it is possible to prevent erroneous detection due to an erroneous setting of the user.

  As mentioned above, the invention made by the present inventor has been specifically described based on the embodiment. However, the present invention is not limited to the above embodiment, and can be changed without departing from the gist thereof.

  For example, in the embodiment, the first motor M1 can be operated as an assist unit, the second motor M2 can be operated as a brake unit, and the operations of the first motor M1 and the second motor are predetermined. It may be switched at a timing (for example, after a predetermined number of sheets have passed). In this case, since heat generated by the rotational resistance when operating as a brake unit can be dispersed, deterioration of the motor due to heat generation can be suppressed.

  Further, for example, in the embodiment, the torque generation unit 64 has been described as having one each of the first motor M1 and the second motor M2, but a plurality of the first motor M1 and the second motor M2 are provided. You may comprise with the motor of.

  Furthermore, the present invention can also be applied to the case where the upper fixing unit 61 is a roller heating method, that is, the fixing roller 611 is a fixing surface side member.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 10 Image reading part 20 Operation display part 30 Image processing part 40 Image forming part 50 Paper conveyance part 60 Fixing part 61 Upper fixing part 611 Fixing roller 612 Heating roller 613 Support roller 614 Fixing belt (fixing surface side member)
62 Lower Fixing Unit 621 Pressure Roller (Back Side Support Member)
63 Heating source 64 Torque generating unit 65 Pressure separation / separation unit M1 First motor (brake unit)
M2 Second motor (assist section)
M3 drive motor (drive unit)
100 control unit (braking force control unit, operation abnormality detection unit)

Claims (5)

A fixing surface side member disposed on the fixing surface side of the paper on which the toner image is formed;
A back-side support member that is disposed on the back side of the sheet and forms a fixing nip that sandwiches and conveys the sheet by being pressed against the fixing-side member;
A drive unit for rotating the back side support member at a predetermined peripheral speed,
An image forming apparatus for fixing a toner image on a sheet passing through the fixing nip by rotating the back surface side support member in a state of being pressed against the fixing surface side member and rotating the fixing surface side member. Because
A torque generating unit that applies a braking force in a direction that prevents rotation to the fixing surface side member;
A braking force control unit that controls the torque generation unit so that a predetermined torque is generated in the back side support member;
An image forming apparatus comprising: an operation abnormality detecting unit that detects an operation abnormality of the torque generating unit based on a driving current supplied to the driving unit when a sheet is passed. The torque generating unit includes a first motor that operates as a brake unit that applies a first torque in a direction that prevents rotation to the fixing surface side member, and a second motor in a direction that assists the rotation of the fixing surface side member. A second motor that operates as an assist unit that applies torque,
The said braking force control part controls the said braking force by adjusting the 1st torque by the said 1st motor, or the 2nd torque by the said 2nd motor. Image forming apparatus.   The operation abnormality detection unit detects an operation abnormality in the first motor when a driving current supplied to the driving unit at the time of passing a sheet is lower than a driving current when a previous sheet is passed by a predetermined value or more. The image forming apparatus according to claim 2, wherein the image forming apparatus is determined to have occurred.   When the operation abnormality detection unit detects an operation abnormality of the torque generation unit, the operation abnormality detection unit operates the first motor with the fixing surface side member and the back surface side support member separated from each other. The image forming apparatus according to claim 3, wherein an operation abnormality of the torque generation unit is determined based on a rotation state. The first motor is configured to be operable as the assist unit,
The second motor is configured to be operable as the brake unit,
5. The image forming apparatus according to claim 2, wherein the braking force control unit switches operations of the first motor and the second motor at a predetermined timing. 6.

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