JP2019101190A - Image forming apparatus - Google Patents

Abstract

To solve such a problem that a size and a cost of an image forming apparatus are increased when a sensor for detecting the presence or absence of a recording medium is provided at a downstream side of a fixing roller.SOLUTION: A distance L from a nip part of a fixing roller 318a to a nip part of a conveyance roller 318b is set to a value shorter than a length π*R (R is a diameter of the fixing roller) of a circumference of the fixing roller 318a. A sheet is detected on the basis of a signal outputted from a motor controller 157 for controlling a motor driving the conveyance roller 318b. As a result, an increase of in size and cost of the image forming apparatus can be suppressed. The recording medium can be easily removed from the fixing roller in comparison with a case where the recording medium is removed from the fixing roller, after one rotation of the fixing roller to which the recording medium adheres is made.SELECTED DRAWING: Figure 5

Description

  The present invention relates to control of a motor in an image forming apparatus.

  2. Description of the Related Art Conventionally, in an image forming apparatus, there is known a fixing device having a fixing roller for fixing a toner image transferred onto a recording medium to the recording medium by heating and pressing.

  In the fixing device, the recording medium which has passed through the nip portion of the fixing roller may not be separated from the fixing roller. That is, the fixing roller may rotate in a state where the recording medium which has passed through the nip portion of the fixing roller is stuck to the fixing roller, and the recording medium may be wound around the fixing roller.

  Patent Document 1 describes a configuration for detecting whether a recording medium is wound around a fixing roller based on a load torque applied to a motor that drives the fixing roller. Specifically, after the load torque is increased due to the leading edge of the recording medium rushing into the nip portion of the fixing roller, the load torque is caused due to the leading edge of the recording medium rushing again into the nip portion. When it increases, it is determined that the recording medium is wound around the fixing roller. That is, according to Patent Document 1, it is determined that the recording medium is wound around the fixing roller when the fixing roller makes one rotation while the recording medium is stuck to the fixing roller. The determination result is notified to the user.

JP, 2017-53961, A

  In Patent Document 1, the user is notified of the determination result after one rotation of the fixing roller to which the recording medium is stuck, so it becomes difficult to remove the recording medium from the fixing roller.

  In this case, it is conceivable to provide a sensor for detecting the presence or absence of the recording medium downstream of the fixing roller in the conveyance direction of the recording medium, but the size of the apparatus increases and the cost increases due to the provision of the sensor. You

  In view of the above problems, an object of the present invention is to suppress an increase in size of an image forming apparatus.

In order to solve the above problems, an image forming apparatus according to the present invention is:
Image forming means for forming an image on a sheet;
A fixing unit that includes a rotating body that supplies heat to a sheet, and fixes the image formed by the image forming unit to the sheet by the heat of the rotating body;
A transport roller that transports the sheet, the transport roller being adjacent to the rotating body and provided downstream of the rotating body in the transport direction in which the sheet is transported;
A motor for driving the transport roller;
Phase determining means for determining the rotational phase of the rotor of the motor;
Controlling a drive current flowing through a winding of the motor such that a deviation between a command phase representing a target phase of the rotor of the motor and a rotational phase of the rotor determined by the phase determination means is reduced Control means,
Second control means for controlling conveyance of the sheet;
Outputting means for outputting a predetermined signal when the absolute value of the value of the parameter corresponding to the load torque applied to the rotor of the motor exceeds a predetermined value;
Have
The distance from the nip of the rotor to the nip of the transport roller is shorter than the circumferential length of the rotor,
The second control means does not output the predetermined signal from the output means in a period from when the leading end of the sheet reaches a predetermined position upstream of the nip portion of the rotating body and until a predetermined time has elapsed In this case, the conveyance of the sheet is stopped.

  According to the present invention, the enlargement of the image forming apparatus can be suppressed.

FIG. 2 is a cross-sectional view illustrating an image forming apparatus. FIG. 3 is a block diagram showing a control configuration of the image forming apparatus. It is a figure which shows the relationship between the two-phase motor which consists of A phase and B phase, and the rotating coordinate system represented by d axis | shaft and q axis | shaft. It is a block diagram showing composition of a motor control device. FIG. 2 is a view for explaining the configuration of a fixing device according to the first embodiment. 5 is a time chart showing a peripheral velocity V1 of a fixing roller and a peripheral velocity V2 of a conveyance roller. It is a figure which shows deviation (DELTA) (theta) output from the motor control apparatus which controls motor M2 which concerns on 1st Embodiment. It is a flowchart explaining the control method of a conveyance roller. FIG. 7 is a diagram for explaining the configuration of a fixing device according to a second embodiment. It is a figure which shows deviation (DELTA) (theta) output from the motor control apparatus which concerns on 2nd Embodiment. It is a flowchart explaining the control method of a conveyance roller. It is a block diagram showing composition of a motor control device which performs speed feedback control.

  The preferred embodiments of the present invention will be described below with reference to the drawings. However, the shapes of the component parts described in this embodiment and their relative positions and the like should be appropriately changed according to the configuration of the apparatus to which the present invention is applied and various conditions, and the scope of the present invention is It is not a thing of the meaning limited to the following embodiment. In the following description, although the case where the motor control device is provided in the image forming apparatus will be described, the provision of the motor control device is not limited to the image forming apparatus. For example, it is also used in a sheet conveying apparatus for conveying a sheet such as a recording medium or an original.

First Embodiment
[Image forming apparatus]
FIG. 1 is a cross-sectional view showing the configuration of a monochrome electrophotographic copying machine (hereinafter referred to as an image forming apparatus) 100 having a sheet conveying apparatus used in the present embodiment. The image forming apparatus is not limited to a copying machine, and may be, for example, a facsimile machine, a printing machine, or a printer. Further, the recording method is not limited to the electrophotographic method, and may be, for example, an inkjet or the like. Furthermore, the format of the image forming apparatus may be either monochrome or color.

  The configuration and functions of the image forming apparatus 100 will be described below with reference to FIG. As shown in FIG. 1, the image forming apparatus 100 includes a document feeding device 201, a reading device 202, and an image printing device 301.

  The originals stacked on the original stacking unit 203 of the original feeding device 201 are fed one by one by the paper feed roller 204 and conveyed along the conveyance guide 206 onto the original glass table 214 of the reading device 202. Further, the document is conveyed by a conveying belt 208 at a constant speed, and is discharged by a discharge roller 205 to a discharge tray (not shown). Reflected light from the original image illuminated by the illumination 209 at the reading position of the reading device 202 is guided to the image reading unit 111 by the optical system including the reflecting mirrors 210, 211 and 212, and converted into an image signal by the image reading unit 111. Be done. The image reading unit 111 includes a lens, a CCD as a photoelectric conversion element, a drive circuit of the CCD, and the like. The image signal output from the image reading unit 111 is output to the image printing apparatus 301 after various correction processes are performed by the image processing unit 112 configured by a hardware device such as an ASIC. As described above, the document is read. That is, the document feeding device 201 and the reading device 202 function as a document reading device.

  Further, as a document reading mode, there are a first reading mode and a second reading mode. The first reading mode is a mode in which an image of a document conveyed at a constant speed is read by an illumination system 209 and an optical system fixed at a predetermined position. The second reading mode is a mode in which an image of a document placed on a document glass 214 of the reading device 202 is read by an illumination system 209 moving at a constant speed and an optical system. Usually, an image of a sheet-like document is read in a first reading mode, and an image of a bound document such as a book or a booklet is read in a second reading mode.

  Sheet storage trays 302 and 304 are provided inside the image printing apparatus 301. The sheet storage trays 302 and 304 can store different types of recording media. For example, A4 size plain paper is stored in the sheet storage tray 302, and thick sheet of A4 size is stored in the sheet storage tray 304. The recording medium is a medium on which an image is formed by the image forming apparatus. For example, a sheet, a resin sheet, a cloth, an OHP sheet, a label, and the like are included in the recording medium.

  The recording medium stored in the sheet storage tray 302 is fed by the paper feed roller 303, and is conveyed by the conveyance roller 306 to the registration roller 308 in the stopped state. Further, the recording medium stored in the sheet storage tray 304 is fed by the sheet feeding roller 305, and is conveyed by the conveyance rollers 307 and 306 to the registration roller 308 in the stopped state.

  The image signal output from the reader 202 is input to an optical scanning device 311 including a semiconductor laser and a polygon mirror. In addition, the outer peripheral surface of the photosensitive drum 309 is charged by the charger 310. After the outer peripheral surface of the photosensitive drum 309 is charged, a laser beam corresponding to an image signal input from the reading device 202 to the light scanning device 311 is photosensitive from the light scanning device 311 via the polygon mirror and mirrors 312 and 313. The outer peripheral surface of the drum 309 is irradiated. As a result, an electrostatic latent image is formed on the outer peripheral surface of the photosensitive drum 309. For charging the photosensitive drum, for example, a charging method using a corona charger or a charging roller is used.

  Subsequently, the electrostatic latent image is developed by the toner in the developing device 314, and a toner image is formed on the outer peripheral surface of the photosensitive drum 309. The toner image formed on the photosensitive drum 309 is transferred onto the recording medium by a transfer charger 315 provided at a position (transfer position) facing the photosensitive drum 309. At the transfer timing, the registration roller 308 starts transporting the recording medium to the transfer position.

  As described above, the recording medium to which the toner image has been transferred is fed to the fixing device 318 by the conveyance belt 317.

  The fixing device 318 has a fixing roller 318a and a conveyance roller 318b. The fixing roller 318a fixes the toner image on the recording medium by heating and pressing. The conveyance roller 318 b conveys the recording medium on which the toner image is fixed by the fixing roller 318 a to the downstream side.

  As described above, the image forming apparatus 100 forms an image on the recording medium.

  When the image formation is performed in the single-sided printing mode, the recording medium having passed through the fixing unit 318 is discharged by the paper discharge rollers 319 and 324 to a paper discharge tray (not shown). When image formation is performed in the double-sided printing mode, the recording medium is subjected to the fixing process on the first surface of the recording medium by the fixing device 318, and then the recording medium is discharged from the discharge roller 319, the conveyance roller 320, and the reverse roller 321 Are transported to the reverse path 325. Thereafter, the recording medium is conveyed again by the conveyance rollers 322 and 323 to the registration roller 308, and an image is formed on the second surface of the recording medium by the method described above. Thereafter, the recording medium is discharged to a discharge tray (not shown) by discharge rollers 319 and 324.

  Further, when the recording medium on which the image is formed on the first surface is discharged to the outside of the image forming apparatus 100 with the face down, the recording medium having passed through the fixing unit 318 passes the discharge roller 319 and the conveyance roller 320 It is transported in the direction of Thereafter, the rotation of the conveyance roller 320 is reversed immediately before the trailing edge of the recording medium passes through the nip portion of the conveyance roller 320, and the recording medium is discharged from the paper discharge roller with the first surface of the recording medium facing downward. The image is discharged to the outside of the image forming apparatus 100 via 324.

  This completes the description of the configuration and functions of the image forming apparatus 100.

  FIG. 2 is a block diagram showing an example of a control configuration of the image forming apparatus 100. As shown in FIG. As shown in FIG. 2, the system controller 151 includes a CPU 151a, a ROM 151b, and a RAM 151c. Further, the system controller 151 includes an image processing unit 112, an operation unit 152, an analog / digital (A / D) converter 153, a high voltage control unit 155, motor control devices 157 and 158, sensors 159, an AC driver 160, and sheet detection. Connected to the container 700. The system controller 151 can transmit and receive data and commands to and from each connected unit.

  The CPU 151a executes various sequences related to a predetermined image forming sequence by reading out and executing various programs stored in the ROM 151b.

  The RAM 151 c is a storage device. The RAM 151 c stores, for example, various data such as setting values for the high voltage control unit 155, command values for the motor control device 157, and information received from the operation unit 152.

  The system controller 151 transmits, to the image processing unit 112, setting value data of various devices provided inside the image forming apparatus 100, which are necessary for image processing in the image processing unit 112. Furthermore, the system controller 151 receives the signal from the sensors 159 and sets the setting value of the high voltage control unit 155 based on the received signal.

  The high voltage control unit 155 supplies necessary voltages to the high voltage unit 156 (the charger 310, the developing device 314, the transfer charger 315, and the like) according to the setting value set by the system controller 151.

  The motor control device 157 controls the motor M2 that drives the conveyance roller 318b in accordance with the command output from the CPU 151a. The motor control device 158 also controls the motor M1 that drives the fixing roller 318a in accordance with the command output from the CPU 151a. Although only the motors M1 and M2 are illustrated as the motors of the image forming apparatus in FIG. 2, actually, the image forming apparatus is provided with three or more motors. In addition, one motor control device may be configured to control a plurality of motors. Furthermore, although only two motor control devices are provided in FIG. 2, actually, three or more motor control devices are provided in the image forming apparatus.

  The A / D converter 153 receives a detection signal detected by the thermistor 154 for detecting the temperature of the fixing heater 161, converts the detection signal from an analog signal to a digital signal, and transmits the digital signal to the system controller 151. The system controller 151 controls the AC driver 160 based on the digital signal received from the A / D converter 153. The AC driver 160 controls the fixing heater 161 so that the temperature of the fixing heater 161 becomes a temperature required to perform the fixing process. The fixing heater 161 is a heater used for the fixing process, and is included in the fixing unit 318.

  The system controller 151 displays the operation screen for the user to set the type of recording medium to be used (hereinafter referred to as a paper type) and the like on the display unit provided in the operation unit 152. Control. The system controller 151 receives information set by the user from the operation unit 152, and controls an operation sequence of the image forming apparatus 100 based on the information set by the user. The system controller 151 also transmits information indicating the state of the image forming apparatus to the operation unit 152. The information indicating the state of the image forming apparatus is, for example, information on the number of formed images, the progress of the image forming operation, and jamming and double feeding of sheet materials in the document reading apparatus 201 and the image printing apparatus 301. The operation unit 152 displays the information received from the system controller 151 on the display unit.

  As described above, the system controller 151 controls the operation sequence of the image forming apparatus 100. The sheet detector 700 will be described later.

[Motor controller]
Next, the motor control device in the present embodiment will be described. The motor control device in the present embodiment controls the motor using vector control.

<Vector control>
First, a method of performing the vector control by the motor control device 157 in the present embodiment will be described using FIGS. 3 and 4. The configuration of the motor control device 158 is the same as the configuration of the motor control device 157, so the description will be omitted. Further, the motor in the following description is not provided with a sensor such as a rotary encoder for detecting the rotational phase of the rotor of the motor, but a sensor such as a rotary encoder may be provided.

  FIG. 3 shows a stepping motor (hereinafter referred to as a motor) M2 consisting of two phases of A phase (first phase) and B phase (second phase), and a rotating coordinate system represented by d axis and q axis FIG. In FIG. 3, in the stationary coordinate system, an α axis which is an axis corresponding to the winding of the A phase and a β axis which is an axis corresponding to the winding of the B phase are defined. Also, in FIG. 3, the d-axis is defined along the direction of the magnetic flux produced by the magnetic poles of the permanent magnets used in the rotor 402, and is a direction 90 degrees counterclockwise from the d-axis (orthogonal to the d-axis The q axis is defined along the The angle between the α axis and the d axis is defined as θ, and the rotational phase of the rotor 402 is represented by the angle θ. In the vector control, a rotational coordinate system based on the rotational phase θ of the rotor 402 is used. Specifically, in vector control, a q-axis component (torque current component) that generates a torque in the rotor, which is a current component in a rotating coordinate system of a current vector corresponding to a drive current flowing through a winding, and a winding The d-axis component (excitation current component) that affects the strength of the magnetic flux passing through is used.

  The vector control is a motor by performing phase feedback control that controls the value of the torque current component and the value of the excitation current component so that the deviation between the command phase representing the target phase of the rotor and the actual rotational phase is reduced. Control method to control the Also, the motor is controlled by performing speed feedback control that controls the value of the torque current component and the value of the excitation current component so that the deviation between the commanded speed representing the target speed of the rotor and the actual rotational speed becomes small. There is also a way.

  FIG. 4 is a block diagram showing an example of the configuration of a motor control device 157 that controls the motor M2. The motor control device 157 is configured by at least one ASIC, and executes each function described below.

  As shown in FIG. 4, the motor control device 157 supplies drive current to the phase controller 502, current controller 503, coordinate inverse converter 505, coordinate converter 511, and motor winding as a circuit performing vector control. PWM inverter 506 and the like. The coordinate converter 511 represents a current vector corresponding to the drive current flowing through the A-phase and B-phase windings of the motor M2 in the q-axis and d-axis from the stationary coordinate system represented by the α-axis and the β-axis. Coordinate conversion to a rotational coordinate system. As a result, the drive current flowing through the winding is represented by the current value (q-axis current) of the q-axis component which is the current value in the rotational coordinate system and the current value (d-axis current) of the d-axis component. The q-axis current corresponds to a torque current that causes the rotor 402 of the motor M2 to generate torque. The d-axis current corresponds to an excitation current that affects the strength of the magnetic flux passing through the winding of the motor M2, and does not contribute to the generation of torque of the rotor 402. The motor controller 157 can independently control the q-axis current and the d-axis current. As a result, the motor control device 157 can efficiently generate the torque necessary for the rotor 402 to rotate by controlling the q-axis current according to the load torque applied to the rotor 402. That is, in vector control, the magnitude of the current vector shown in FIG. 3 changes in accordance with the load torque applied to the rotor 402.

  The motor control device 157 determines the rotational phase θ of the rotor 402 of the motor M2 by a method described later, and performs vector control based on the determination result. The CPU 151a generates a command phase θ_ref representing a target phase of the rotor 402 of the motor M2 and outputs the command phase θ_ref to the motor control device 157. The command phase θ_ref is set based on the target speed of the rotor of the motor M2 corresponding to the target speed of the circumferential speed of the transport roller 318b.

  The subtractor 101 calculates and outputs the deviation Δθ between the rotational phase θ of the rotor 402 of the motor M2 and the command phase θ_ref, which is output from the phase determiner 513.

  The phase controller 502 acquires the deviation Δθ in a cycle T (for example, 200 μs). The phase controller 502 controls the q-axis current command value iq_ref and the d-axis so that the deviation Δθ obtained from the subtractor 101 becomes smaller based on proportional control (P), integral control (I), and differential control (D). The current command value id_ref is generated and output. Specifically, the phase controller 502 sets the q-axis current command value iq_ref and the d-axis current command value id_ref such that the deviation Δθ obtained from the subtractor 101 becomes zero based on P control, I control, and D control. Generate and output The P control is a control method of controlling the value of an object to be controlled based on a value proportional to the deviation between the command value and the estimated value. Moreover, I control is a control method which controls the value of the control object based on the value proportional to the time integral of the deviation of a command value and an estimated value. Moreover, D control is a control method which controls the value of the object to control based on the value proportional to the time change of the deviation of a command value and an estimated value. The phase controller 502 in this embodiment generates the q-axis current command value iq_ref and the d-axis current command value id_ref based on PID control, but is not limited to this. For example, the phase controller 502 may generate the q-axis current command value iq_ref and the d-axis current command value id_ref based on PI control. When a permanent magnet is used for the rotor 402, the d-axis current command value id_ref that normally affects the strength of the magnetic flux passing through the winding is set to 0, but is not limited to this.

  The drive currents flowing through the A-phase and B-phase windings of the motor M2 are detected by the current detectors 507 and 508, and then converted from analog values to digital values by the A / D converter 510. The period in which the current detectors 507 and 508 detect the current is, for example, a period (for example, 25 μs) equal to or less than the period T in which the phase controller 502 acquires the deviation Δθ.

The current value of the drive current converted from an analog value to a digital value by A / D converter 510 is expressed by the following equation using the phase θe of the current vector shown in FIG. 3 as current values iα and iβ in the stationary coordinate system. expressed. The phase θe of the current vector is defined as the angle between the α axis and the current vector. Also, I indicates the magnitude of the current vector.
iα = I * cos θe (1)
iβ = I * sin θe (2)

  The current values iα and iβ are input to the coordinate converter 511 and the induced voltage determiner 512.

The coordinate converter 511 converts the current values iα and iβ in the stationary coordinate system into the current value iq of the q-axis current and the current value id of the d-axis current according to the following equations.
id = cosθ * iα + sinθ * iβ (3)
iq = −sin θ * iα + cos θ * iβ (4)

  The coordinate converter 511 outputs the converted current value iq to the subtractor 102. Further, the coordinate converter 511 outputs the converted current value id to the subtractor 103.

  The subtractor 102 calculates a deviation between the q-axis current command value iq_ref and the current value iq, and outputs the deviation to the current controller 503.

  Further, the subtractor 103 calculates a deviation between the d-axis current command value id_ref and the current value id, and outputs the deviation to the current controller 503.

  The current controller 503 generates the drive voltages Vq and Vd based on the PID control so that the input deviations become smaller. Specifically, the current controller 503 generates the drive voltages Vq and Vd so that the input deviations become 0, respectively, and outputs the drive voltages Vq and Vd to the coordinate inverse transformer 505. That is, the current controller 503 functions as a generation unit. Although the current controller 503 in the present embodiment generates the drive voltages Vq and Vd based on PID control, the present invention is not limited to this. For example, the current controller 503 may generate the drive voltages Vq and Vd based on PI control.

The coordinate inverse transformer 505 inversely converts the drive voltages Vq and Vd in the rotational coordinate system output from the current controller 503 into drive voltages Vα and Vβ in the stationary coordinate system according to the following equations.
Vα = cos θ * Vd-sin θ * Vq (5)
Vβ = sin θ * Vd + cos θ * Vq (6)

  The coordinate inverse transformer 505 outputs the inversely transformed Vα and Vβ to the induced voltage determiner 512 and the PWM inverter 506.

  The PWM inverter 506 has a full bridge circuit. The full bridge circuit is driven by a PWM signal based on the drive voltages Vα and Vβ input from the coordinate inverse converter 505. As a result, the PWM inverter 506 generates drive currents iα and iβ according to the drive voltages Vα and Vβ, and drives the motor M2 by supplying the drive currents iα and iβ to the windings of each phase of the motor M2. . That is, the PWM inverter 506 functions as a supply means for supplying current to the windings of each phase of the motor M2. In the present embodiment, the PWM inverter has a full bridge circuit, but the PWM inverter may be a half bridge circuit or the like.

Next, a method of determining the rotational phase θ will be described. For determining the rotational phase θ of the rotor 402, values of induced voltages Eα and Eβ induced in the A-phase and B-phase windings of the motor M2 by the rotation of the rotor 402 are used. The value of the induced voltage is determined (calculated) by the induced voltage determiner 512. Specifically, the induced voltages Eα and Eβ are input from the A / D converter 510 to the current value iα and iβ input to the induced voltage determiner 512, and from the coordinate inverse converter 505 to the induced voltage determiner 512. It is determined from the drive voltages Vα and Vβ by the following equation.
Eα = Vα-R * iα-L * diα / dt (7)
Eβ = Vβ-R * iβ-L * diβ / dt (8)

  Here, R is a winding resistance, and L is a winding inductance. The values of the winding resistance R and the winding inductance L are values specific to the motor M2 used, and are stored in advance in a memory (not shown) or the like provided in the ROM 151b or the motor control device 157.

  The induced voltages Eα and Eβ determined by the induced voltage determiner 512 are output to the phase determiner 513.

The phase determiner 513 determines the rotational phase θ of the rotor 402 of the motor M2 according to the following equation based on the ratio between the induced voltage Eα and the induced voltage Eβ output from the induced voltage determiner 512.
θ = tan ^ −1 (−Eβ / Eα) (9)

  In the present embodiment, the phase determiner 513 determines the rotational phase θ by performing the calculation based on the equation (9), but the present invention is not limited to this. For example, the phase determiner 513 performs rotation by referring to a table stored in the ROM 151b or the like, which indicates the relationship between the induced voltage Eα and the induced voltage Eβ and the rotational phase θ corresponding to the induced voltage Eα and the induced voltage Eβ. The phase θ may be determined.

  The rotational phase θ of the rotor 402 obtained as described above is input to the subtractor 101, the coordinate inverse transformer 505, and the coordinate converter 511.

  The motor control device 157 repeatedly performs the control described above.

  As described above, the motor control device 157 in the present embodiment performs vector control to control the current value in the rotational coordinate system so that the deviation between the command phase θ_ref and the rotational phase θ becomes smaller. By performing the vector control, it is possible to suppress that the motor is out of step and that the motor noise and the power consumption increase due to the surplus torque.

[Fixer Configuration]
FIG. 5 is a view for explaining the configuration of the fixing device in the present embodiment. As shown in FIG. 5, the fixing roller 318 a is driven by a stepping motor (hereinafter referred to as a motor) M 1, and the motor M 1 is controlled by a motor control device 158. Further, the conveyance roller 318 b adjacent to the fixing roller 318 a is driven by the motor M 2, and the motor M 2 is controlled by the motor control device 157.

  In the present embodiment, the distance L from the nip portion of the fixing roller 318a to the nip portion of the conveyance roller 318b is set to a value shorter than the circumferential length (circumferential length) π * R of the fixing roller 318a. Here, R is the diameter of the fixing roller.

  Further, in the present embodiment, the distance L from the nip portion of the fixing roller 318 a to the nip portion of the conveyance roller 318 b is the minimum length of sheets in the conveyance direction among the sheets permitted to be conveyed in the image forming apparatus 100. It is set to a value shorter than the sheet length.

  The sheet detector 700 detects whether or not the leading end of the sheet has reached the nip portion of the conveyance roller 318b by a method described later, and outputs the detection result to the CPU 151a. The CPU 151a determines, based on the detection result, whether or not an abnormality has occurred in sheet conveyance (whether or not the sheet is wound around the fixing roller).

<Configuration for Determining Whether or Not Sheet is Wrapped on Fixing Roller>
The configuration for determining whether the sheet is wound around the fixing roller will be described below. In the present embodiment, the following configuration is applied to suppress an increase in the size of the image forming apparatus.

{How to detect the edge of the sheet}
Hereinafter, a method of determining (detecting) whether the sheet detector 700 has reached the nip portion of the conveyance roller 318b will be described. In the present embodiment, whether or not the leading end of the sheet has reached the nip portion of the conveyance roller 318 b is determined not based on a sensor such as a photo sensor but based on a signal output from the motor control device 157 . The sheet detector 700 outputs the detection result, for example, at a predetermined time cycle (for example, a cycle in which the deviation Δθ is input).

  In the following description, the motor control devices 157 and 158 perform phase feedback control based on the command phase θ_ref output from the CPU 151a, but the command phase θ_ref is generated by the CPU 151a based on the target speed of the motors M1 and M2. Be done. In practice, the CPU 151a outputs a pulse signal to each of the motor control devices 157 and 158, the number of pulses corresponds to the command phase, and the frequency of the pulses corresponds to the target velocity. Also, the target speed is determined based on the target value of the peripheral speed of the roller.

  FIG. 6 is a time chart showing the peripheral velocity V1 of the fixing roller 318a and the peripheral velocity V2 of the conveyance roller 318b. FIG. 6A shows the circumferential velocity V1 of the fixing roller 318a. FIG. 6B is a diagram showing the peripheral velocity V2 of the transport roller 318b.

  In the present embodiment, the motor M2 is controlled such that the peripheral velocity V2 of the conveyance roller 318b is VP2, and the motor M1 is controlled such that the peripheral velocity V1 of the fixing roller 318a is VP1. The circumferential velocity VP2 of the conveyance roller 318b is a value larger by ΔV than the circumferential velocity VP1 of the fixing roller 318a. That is, the conveying roller 318 b rotates at a peripheral speed ΔV faster than that of the fixing roller 318 a.

  Thus, by setting the circumferential speed of the conveyance roller 318b to a circumferential speed higher than the circumferential speed of the fixing roller 318a, the recording medium is prevented from being bent between the conveyance roller 318b and the fixing roller 318a. be able to. As a result, the recording medium after fixing contacts with the fixing roller due to the bending of the recording medium between the conveying roller 318 b and the fixing roller 318 a, and the image can be prevented from being distorted.

  Further, by setting the circumferential speed of the conveyance roller 318b to a circumferential speed higher than the circumferential speed of the fixing roller 318a, the conveyance roller 306 and the conveyance roller 307 have the same accuracy in detecting the sheet, as described later. Better than rotating at speed. The speed difference ΔV is set such that the image fixed on the sheet is not damaged even if the conveyance roller 306 slips on the surface of the sheet conveyed by the conveyance roller 307 rotating at the peripheral speed V1. Be done. In the present embodiment, for example, the peripheral speed difference ΔV when the type of sheet to be conveyed is thick paper is the same peripheral speed difference as the peripheral speed difference ΔV when thin paper.

  FIG. 7 is a diagram showing the deviation Δθ output from the motor control device 157 that controls the motor M2 that drives the conveyance roller 318b. In FIG. 7, the fact that the deviation Δθ is a negative value means that the rotational phase θ is behind the command phase θ_ref, and the fact that the deviation Δθ is a positive value is that the rotational phase θ is a command phase It means that it is ahead of θ_ref. However, the relationship between the polarity of the deviation Δθ and the rotational phase θ and the command phase θ_ref is not limited to this. For example, the configuration may be such that the deviation Δθ is a positive value when the rotational phase θ is behind the command phase θ_ref, and the deviation Δθ is a negative value when the rotational phase θ leads the command phase θ_ref. .

  In the present embodiment, the sheet is conveyed by the fixing roller 318a that rotates at the peripheral speed VP1. Further, the CPU 151a starts driving of the transport roller 318b at time t0 set by the operation sequence of the image forming apparatus 100 determined in advance. The peripheral velocity VP1 of the fixing roller 318a is a transport velocity at which the sheet is transported. Further, the peripheral velocity V2 of the conveyance roller 318b is set to a peripheral velocity VP2 which is larger by ΔV than the peripheral velocity VP1. Also, at time t0 when the driving of the conveyance roller 318b is started, the circumferential speed of the conveyance roller 318b reaches VP2 before the leading edge of the sheet conveyed by the fixing roller 318a reaches the nip portion of the conveyance roller 318b. Set to

  The torque applied to the conveyance roller 306 when the sheet is conveyed by both the conveyance roller 307 and the conveyance roller 306 is higher than when the conveyance roller 306 rotates at the same peripheral speed as the conveyance roller 307. It is larger when rotating at a high peripheral speed. This is because, when the conveyance roller 306 rotates at a peripheral speed faster than the conveyance roller 307, the conveyance roller 306 pulls the sheet nipped by the conveyance roller 307 to the downstream side. When the load torque applied to the conveyance roller 306 increases, the absolute value of the deviation Δθ increases because the rotational phase θ of the rotor of the motor M2 that drives the conveyance roller 306 lags behind the command phase θ_ref. Specifically, for example, as shown in FIG. 7, the absolute value of the deviation Δθ increases at time t1 when the conveyance of the sheet by the conveyance roller 306 is started (the sheet is nipped by the conveyance roller 306). As described above, by driving the conveying roller 306 at a speed faster than that of the conveying roller 307, the fluctuation range of the load torque when the leading end of the sheet is nipped by the nip portion of the conveying roller 306 can be increased.

  In the present embodiment, a threshold Δθth is set as a threshold (predetermined value) of the deviation Δθ for determining whether or not the conveyance of the sheet by the conveyance roller 318b is started (the sheet is nipped by the conveyance roller 318b). There is.

  The sheet detector 700 determines whether the absolute value of the deviation Δθ has become equal to or larger than a threshold Δθth. When the absolute value of the deviation Δθ becomes equal to or larger than the threshold Δθth, the sheet detector 700 detects a signal indicating that the conveyance of the sheet by the conveyance roller 318b is started (the sheet is nipped by the conveyance roller 318b) as a detection result to the CPU 151a. Output. When the absolute value of the deviation Δθ is less than the threshold value Δθth, the sheet detector 700 outputs a signal indicating that the leading end of the sheet has not reached the nip portion of the conveyance roller 318b to the CPU 151a as a detection result.

  In the present embodiment, among the types of sheets that can be conveyed in the image forming apparatus 100, the threshold Δθth is set based on the type of sheet with the smallest load fluctuation occurring on the conveyance roller when the sheet is conveyed. . Specifically, for example, in the case where the type of sheet that can be conveyed in the image forming apparatus 100 is thick paper, plain paper, thin paper, load fluctuation occurring in the discharge roller when the leading end of the thick paper is conveyed is plain paper or It is larger than the load fluctuation that occurs on the discharge roller when thin paper is conveyed. Further, the load fluctuation occurring on the paper discharge roller when the plain paper is transported is larger than the load fluctuation occurring on the paper discharge roller when the thin paper is transported. Therefore, the threshold value Δθth is set based on the load fluctuation that occurs on the paper discharge roller when thin paper is conveyed.

  The threshold value Δθth is, for example, a value larger than the absolute value of the deviation Δθ assumed in a state where thin paper (sheet) is not nipped by the nip portion of the conveyance roller 318 b and the conveyance roller 318 b rotates at a constant speed. Set to Further, the threshold value Δθth is set to a value smaller than the maximum value (peak value) of the absolute value of the deviation Δθ which is increased by the thin paper (sheet) being conveyed by the fixing roller 318a and the conveyance roller 318b. That is, the fact that the absolute value of the deviation Δθ becomes equal to or larger than the threshold value Δθth means that the leading end of the sheet has reached the nip portion of the transport roller 318 b.

  As described above, in the present embodiment, the downstream conveyance roller 318 b in the sheet conveyance direction is driven at a speed higher than that of the upstream fixing roller 318 a. As a result, the fluctuation width of the load torque when the leading end of the sheet is nipped by the nip portion of the conveyance roller 318 b can be made relatively large. As a result, sheet detection can be performed with high accuracy.

{Method to determine whether the sheet is wound around the fuser roller}
FIG. 8 is a flowchart for explaining the control method of the transport roller 318b. Hereinafter, control of the conveyance roller 318b will be described with reference to FIG. The processing of this flowchart is executed by the CPU 151a.

  First, when the enable signal 'H' is output from the CPU 151a to the motor control device 157, the motor control device 157 starts driving of the motor M2 based on the command output from the CPU 151a. As a result, driving of the conveyance roller 318 b is started. The enable signal is a signal that permits or prohibits the operation of the motor control device 157. When the enable signal is 'L (low level)', the CPU 151a prohibits the operation of the motor control device 157. That is, the control of the motor M2 by the motor control device 157 is ended. When the enable signal is 'H (high level)', the CPU 151a permits the operation of the motor control device 157, and the motor control device controls the motor M2 based on the command output from the CPU 151a.

  Next, in S1001, the CPU 151a outputs, to the motor control device 158, an instruction to control the motor M1 so that the circumferential speed of the fixing roller 318a is rotated at VP1. As a result, the motor control device 158 controls the motor M1 so that the fixing roller 318a rotates at the peripheral speed VP1. Further, the CPU 151a outputs, to the motor control device 157, an instruction to control the motor M2 so that the conveyance roller 318b rotates at a circumferential velocity VP2 larger by ΔV than the circumferential velocity VP1 of the fixing roller 318a. As a result, the motor control device 157 controls the motor M2 so that the transport roller 318b rotates at the peripheral velocity VP2.

  In S1002, when the absolute value of the deviation Δθ changes from a value smaller than the threshold Δθth to a value larger than the threshold Δθth, that is, a signal from the sheet detector 700 indicating that the leading end of the sheet has reached the nip portion of the transport roller 318b is the CPU 151a. If it is input, the process proceeds to S1003.

  If the print job ends in S1003, the CPU 151a stops the driving of the conveyance roller 318b and the fixing roller 318a in S1008, and ends the processing of this flowchart.

  In S1002, if the absolute value of the deviation Δθ is less than the threshold Δθth, that is, a signal indicating that the front end of the sheet has not reached the nip portion of the conveyance roller 318b is input from the sheet detector 700 to the CPU 151a. Then, the process proceeds to S1004.

  If, in S1004, the predetermined time T1 has not elapsed since the registration roller 308 started conveying the sheet to the transfer position, the process returns to S1002.

  If the predetermined time T1 has elapsed without the absolute value of the deviation Δθ becoming equal to or larger than the threshold Δθth1 after the registration roller 308 starts conveying the sheet to the transfer position in S1004, the process proceeds to S1005.

  In S1005, the CPU 151a controls the AC driver 160 not to supply power to the fixing heater 161. As a result, the heating of the fixing device by the fixing heater 161 is stopped.

  Thereafter, in S1006, the CPU 151a stops the driving of the fixing roller 318a and the conveyance roller 318b.

  The predetermined time T1 is longer than the time taken for the sheet to reach the nip portion of the conveyance roller 318b from the timing when the registration roller 308 starts conveying the sheet to the transfer position. Further, for the predetermined time T1, a sheet of the distance which is the sum of the distance from the nip of the registration roller 308 to the nip of the fixing roller 318a and the circumferential length π * R of the fixing roller 318a It is a time shorter than the time until it is done.

  After that, in S1007, the CPU 151a displays on the display unit provided in the operation unit 152 that an abnormality (for example, winding of the sheet to the fixing roller 318a, delay jam, etc.) has occurred in sheet conveyance. Inform. As described above, it is determined whether or not the sheet is normally transported by determining whether or not a predetermined time T1 has elapsed since the registration roller 308 started transporting the sheet to the transfer position. be able to.

  As described above, in the present embodiment, the sheet is detected based on a signal output from the motor control device 157 instead of a sensor such as a photosensor. As a result, increase in size and cost of the image forming apparatus can be suppressed.

  Further, in the present embodiment, the distance L from the nip portion of the fixing roller 318a to the nip portion of the conveying roller 318b is longer than the circumferential length π * R of the fixing roller 318a (R is the diameter of the fixing roller). Set to a short value. When the registration roller 308 starts conveying the sheet to the transfer position and the absolute value of the deviation Δθ is smaller than the threshold Δθth for a predetermined time T1, the CPU 151a stops the power supply to the fixing heater. The driving of the fixing roller 318a and the conveyance roller 318b is stopped. Then, the CPU 151a notifies the user by displaying on the display unit provided in the operation unit 152 that an abnormality (for example, winding of the sheet to the fixing roller 318a, delay jam, etc.) has occurred in sheet conveyance. As a result, it is possible to remove the recording medium from the fixing roller more easily than in the case of removing the recording medium from the fixing roller after one rotation of the fixing roller to which the recording medium is stuck.

  In the present embodiment, when the registration roller continues to convey the sheet to the transfer position for a predetermined time T1 after the registration roller starts conveying the sheet, power is supplied to the fixing heater when the absolute value of the deviation Δθ is less than the threshold Δθth. It is stopped and sheet conveyance is stopped, but not limited to this. For example, when the absolute value of the deviation Δθ is less than the threshold Δθth and continues for a predetermined time after the sheet reaches a predetermined position on the upstream side of the conveyance roller 318 b, the power supply to the fixing heater is stopped, and the sheet is conveyed May be stopped. The predetermined time is longer than the time it takes from when the sheet reaches the predetermined position to when the sheet reaches the nip portion of the conveyance roller 318 b. Further, for a predetermined time, a sheet of the distance obtained by adding the distance from the nip portion of registration roller 308 to the nip portion of fixing roller 318a and the circumferential length π * R of fixing roller 318a from the timing is conveyed The time is shorter than the time to

Second Embodiment
The description of the parts having the same configuration as that of the first embodiment will be omitted.

  In the first embodiment, the motor for driving the conveyance roller 318b is a motor different from the motor for driving the fixing roller 318a. That is, in the first embodiment, the conveyance roller 318 b and the fixing roller 318 a are independently driven, and it is determined whether the sheet is wound around the fixing roller based on a signal related to a motor that drives the conveyance roller 318 b.

  In this embodiment, a method will be described in which it is determined whether the sheet is wound around the fixing roller in a configuration in which the motor for driving the conveyance roller 318b is the same motor as the motor for driving the fixing roller 318a.

[Fixer Configuration]
FIG. 9 is a view for explaining the configuration of the fixing device in the present embodiment. As shown in FIG. 9, the fixing roller 318 a and the conveyance roller 318 b are driven by the motor M 2, and the motor M 2 is controlled by the motor control device 157.

  In the present embodiment, the distance L from the nip portion of the fixing roller 318a to the nip portion of the conveying roller 318b is a value shorter than the circumferential length π * R (R is the diameter of the fixing roller) of the fixing roller 318a. Set to

  Further, in the present embodiment, the distance L from the nip portion of the fixing roller 318 a to the nip portion of the conveyance roller 318 b is the minimum length of sheets in the conveyance direction among the sheets permitted to be conveyed in the image forming apparatus 100. It is set to a value shorter than the sheet length.

  The sheet detector 700 detects whether or not the leading end of the sheet has reached the nip portion of the conveyance roller 318 b by the method described in the first embodiment, and outputs the detection result to the CPU 151 a. The CPU 151a determines whether the sheet is wound around the fixing roller based on the detection result.

  In the present embodiment, the rotational force transmitted from the motor M2 to the conveyance roller 318b is adjusted by, for example, a gear or the like so that the circumferential velocity V2 of the conveyance roller 318b becomes ΔV larger than the circumferential velocity V1 of the fixing roller 318a. Ru.

  Thus, by setting the circumferential speed of the conveyance roller 318b to a circumferential speed higher than the circumferential speed of the fixing roller 318a, the recording medium is prevented from being bent between the conveyance roller 318b and the fixing roller 318a. be able to. As a result, the recording medium after fixing contacts with the fixing roller due to the bending of the recording medium between the conveying roller 318 b and the fixing roller 318 a, and the image can be prevented from being distorted.

  Further, as described in the first embodiment, by setting the peripheral speed of the conveyance roller 318b to a peripheral speed higher than the peripheral speed of the fixing roller 318a, the accuracy with which the sheet is detected is the conveyance roller 306 and the conveyance roller. This is better than the case where 307 and the same circumferential speed rotate.

  FIG. 10 is a diagram showing the deviation Δθ output from the motor control device 157. In FIG. 10, that the deviation Δθ is a negative value means that the rotational phase θ is behind the command phase θ_ref, and that the deviation Δθ is a positive value is that the rotational phase θ is a command phase It means that it is ahead of θ_ref. However, the relationship between the polarity of the deviation Δθ and the rotational phase θ and the command phase θ_ref is not limited to this. For example, the configuration may be such that the deviation Δθ is a positive value when the rotational phase θ is behind the command phase θ_ref, and the deviation Δθ is a negative value when the rotational phase θ leads the command phase θ_ref. .

  In the present embodiment, a threshold value Δθth1 (predetermined value) is set as a threshold value of the deviation Δθ for determining whether or not the sheet conveyance by the fixing roller 318a is started (the sheet is nipped by the fixing roller 318a). There is. Further, a threshold value Δθth2 is set as a threshold value of the deviation Δθ for determining whether the conveyance of the sheet by the conveyance roller 318b is started (the sheet is nipped by the conveyance roller 318b).

  The sheet detector 700 determines whether the absolute value of the deviation Δθ has become equal to or greater than a threshold Δθth1. When the absolute value of the deviation Δθ becomes equal to or larger than the threshold Δθth1, the sheet detector 700 detects, as a detection result, a signal indicating that the sheet conveyance by the fixing roller 318a is started (the sheet is nipped by the fixing roller 318a). Output. When the absolute value of the deviation Δθ is less than the threshold value Δθth1, the sheet detector 700 outputs a signal indicating that the leading end of the sheet has not reached the nip portion of the fixing roller 318a to the CPU 151a as a detection result.

  When the absolute value of the deviation Δθ becomes equal to or larger than the threshold Δθth1, next, the sheet detector 700 determines whether the absolute value of the deviation Δθ becomes equal to or larger than the threshold Δθth2. When the absolute value of the deviation Δθ becomes equal to or larger than the threshold Δθth2, the sheet detector 700 detects a signal indicating that the conveyance of the sheet by the conveyance roller 318b is started (the sheet is nipped by the conveyance roller 318b) as a detection result to the CPU 151a. Output. If the absolute value of the deviation Δθ is less than the threshold Δθth2, the sheet detector 700 outputs a signal indicating that the leading end of the sheet has not reached the nip portion of the transport roller 318b as a detection result.

  In the present embodiment, among the types of sheets that can be conveyed in the image forming apparatus 100, the threshold values Δθth1 and Δθth2 are set based on the type of sheet with the smallest load fluctuation occurring on the conveyance roller when the sheet is conveyed. Be done. Specifically, for example, in the case where the type of sheet that can be conveyed in the image forming apparatus 100 is thick paper, plain paper, thin paper, load fluctuation occurring in the discharge roller when the leading end of the thick paper is conveyed is plain paper or It is larger than the load fluctuation that occurs on the discharge roller when thin paper is conveyed. Further, the load fluctuation occurring on the paper discharge roller when the plain paper is transported is larger than the load fluctuation occurring on the paper discharge roller when the thin paper is transported. Therefore, the threshold values Δθth1 and Δθth2 are set based on the load fluctuation that occurs on the paper discharge roller when the thin paper is conveyed.

  The threshold value Δθth1 is, for example, a value larger than the absolute value of the deviation Δθ assumed when the thin paper (sheet) is not nipped by the nip portion of the fixing roller 318a and the fixing roller 318a is rotating at a constant speed. Set to Further, the threshold value Δθth1 is set to a value smaller than the maximum value (peak value) of the absolute value of the deviation Δθ which is increased when the thin paper (sheet) is nipped by the nip portion of the fixing roller 318a. That is, the fact that the absolute value of the deviation Δθ becomes equal to or larger than the threshold value Δθ th1 means that the leading end of the sheet has reached the nip portion of the fixing roller 318a.

  Further, for example, the threshold value Δθth2 is based on the absolute value of the deviation Δθ assumed in a state in which the thin paper (sheet) is not nipped by the nip portion of the conveyance roller 318b and the conveyance roller 318b rotates at a constant speed. It is set to a large value. The threshold value Δθth2 is set to a value smaller than the maximum value (peak value) of the absolute value of the deviation Δθ which is increased by the thin paper (sheet) being conveyed by the fixing roller 318a and the conveyance roller 318b. That is, the fact that the absolute value of the deviation Δθ becomes equal to or greater than the threshold value Δθ th2 means that the leading end of the sheet has reached the nip portion of the transport roller 318 b.

  As described above, in the present embodiment, the downstream conveyance roller 318 b in the sheet conveyance direction is driven at a speed higher than that of the upstream fixing roller 318 a. As a result, the fluctuation width of the load torque when the leading end of the sheet is nipped by the nip portion of the conveyance roller 318 b can be made relatively large. As a result, sheet detection can be performed with high accuracy.

  FIG. 11 is a flowchart illustrating the control method of the transport roller 318b. Hereinafter, control of the conveyance roller 318b will be described with reference to FIG. The processing of this flowchart is executed by the CPU 151a.

  First, when the enable signal 'H' is output from the CPU 151a to the motor control device 157, the motor control device 157 starts driving of the motor M2 based on the command output from the CPU 151a. As a result, driving of the conveyance roller 318 b is started. The enable signal is a signal that permits or prohibits the operation of the motor control device 157. When the enable signal is 'L (low level)', the CPU 151a prohibits the operation of the motor control device 157. That is, the control of the motor M2 by the motor control device 157 is ended. When the enable signal is 'H (high level)', the CPU 151a permits the operation of the motor control device 157, and the motor control device controls the motor M2 based on the command output from the CPU 151a.

  Next, in S2001, the CPU 151a outputs, to the motor control device 157, an instruction to control the motor M2 so that the fixing roller 318a and the conveyance roller 318b rotate. As a result, the motor control device 157 controls the motor M2 so that the fixing roller 318a and the conveying roller 318b rotate.

  When the absolute value of the deviation Δθ changes from a value smaller than the threshold Δθth1 to a value larger than the threshold Δθth1 in S2002, that is, a signal from the sheet detector 700 indicating that the leading edge of the sheet has reached the nip portion of the fixing roller 318a is the CPU 151a. If it is input to, the process proceeds to S2003.

  When the absolute value of the deviation Δθ changes from a value smaller than the threshold Δθth2 to a value larger than the threshold Δθth2 in S2003, that is, a signal from the sheet detector 700 indicating that the leading end of the sheet has reached the nip portion of the transport roller 318b is the CPU 151a. If it is input to the process, the process advances to step S2004.

  If the print job ends in S2004, the CPU 151a stops the driving of the conveyance roller 318b and the fixing roller 318a in S2005, and ends the processing of this flowchart.

  Further, in S2003, if the absolute value of the deviation Δθ is less than the threshold Δθth2, that is, a signal indicating that the leading end of the sheet has not reached the nip portion of the conveyance roller 318b is input from the sheet detector 700 to the CPU 151a. The processing proceeds to step S2006.

  In S2006, if the predetermined time T2 has not elapsed since the absolute value of the deviation Δθ becomes equal to or larger than the threshold Δθth1, the process returns to S2003 again.

  If the predetermined time T2 has elapsed without the absolute value of the deviation Δθ becoming equal to or larger than the threshold Δθth2 after the absolute value of the deviation Δθ becomes equal to or larger than the threshold Δθth1 in S2006, the process proceeds to S2007.

  In step S2007, the CPU 151a controls the AC driver 160 not to supply power to the fixing heater 161. As a result, the heating of the fixing device by the fixing heater 161 is stopped.

  Thereafter, in S2008, the CPU 151a stops the driving of the fixing roller 318a and the conveyance roller 318b.

  The predetermined time T2 is longer than the time taken for the sheet to reach the nip portion of the transport roller 318b after the absolute value of the deviation Δθ becomes equal to or greater than the threshold Δθth1. Further, the predetermined time T2 is a time shorter than the time from when the absolute value of the deviation Δθ becomes equal to or more than the threshold Δθth1 by the length of the circumference π * R of the fixing roller 318a.

  After that, in S2009, the CPU 151a displays on the display unit provided in the operation unit 152 that an abnormality (for example, winding of the sheet to the fixing roller 318a, delay jam, etc.) has occurred in sheet conveyance. Inform.

  Further, in S2002, if the absolute value of the deviation Δθ is less than the threshold Δθth1, a signal indicating that the front end of the sheet has not reached the nip portion of the fixing roller 318a is input from the sheet detector 700 to the CPU 151a. Then, the process proceeds to S2010.

  If the predetermined time T3 has not elapsed since the registration roller 308 started conveying the sheet to the transfer position in S2010, the process returns to S2002 again.

  In S2010, if the predetermined time T3 has elapsed without the absolute value of the deviation Δθ becoming equal to or greater than the threshold Δθ th1 after the registration roller 308 starts conveying the sheet to the transfer position, the CPU 151a performs the process in S2011. Advance to

  In step S2011, the CPU 151a controls the AC driver 160 not to supply power to the fixing heater 161. As a result, the heating of the fixing device by the fixing heater 161 is stopped.

  After that, in S2012, the CPU 151a stops the driving of the fixing roller 318a and the conveyance roller 318b.

  The predetermined time T3 is longer than the time taken for the sheet to reach the nip portion of the fixing roller 318a from the timing when the registration roller 308 starts conveying the sheet to the transfer position. Furthermore, the predetermined time T3 is shorter than the time from the timing until the leading end of the sheet reaches the nip portion of the conveyance roller 318b.

  After that, in step S2013, the CPU 151a notifies the user by displaying on the display unit provided in the operation unit 152 that an abnormality (for example, delay jam) has occurred in sheet conveyance.

  As described above, in the present embodiment, the sheet is detected based on a signal output from the motor control device 157 instead of a sensor such as a photosensor. As a result, increase in size and cost of the image forming apparatus can be suppressed.

  Further, in the present embodiment, the distance L from the nip portion of the fixing roller 318a to the nip portion of the conveying roller 318b is longer than the circumferential length π * R of the fixing roller 318a (R is the diameter of the fixing roller). Set to a short value.

  If the state where the absolute value of the deviation Δθ is smaller than the threshold Δθth1 continues for a predetermined time T3 after the registration roller 308 starts conveying the sheet to the transfer position, the CPU 151a stops the power supply to the fixing heater to fix it. The driving of the roller 318a and the conveyance roller 318b is stopped. Then, the CPU 151a notifies the user by displaying on the display unit provided in the operation unit 152 that an abnormality (for example, delayed jamming) has occurred in sheet conveyance. As a result, it is possible to remove the recording medium from the fixing roller more easily than in the case of removing the recording medium from the fixing roller after one rotation of the fixing roller to which the recording medium is stuck.

  When the absolute value of the deviation Δθ becomes equal to or larger than the threshold Δθth1 and the absolute value of the deviation Δθ continues to be smaller than the threshold Δθth2 for a predetermined time T2, the CPU 151a stops the power supply to the fixing heater and the fixing roller 318a. And stop the driving of the conveyance roller 318b. Then, the CPU 151a notifies the user by displaying on the display unit provided in the operation unit 152 that an abnormality (for example, winding of the sheet to the fixing roller 318a, delay jam, etc.) has occurred in sheet conveyance. As a result, it is possible to remove the recording medium from the fixing roller more easily than in the case of removing the recording medium from the fixing roller after one rotation of the fixing roller to which the recording medium is stuck.

  In the first and second embodiments, when the registration roller 308 starts conveying the sheet to the transfer position and the absolute value of the deviation Δθ continues to be less than the threshold value for a predetermined time, the fixing heater is used. Power supply is stopped, and the driving of the fixing roller 318a and the conveyance roller 318b is stopped.

  In the present embodiment, when the registration roller continues to convey the sheet to the transfer position for a predetermined time T3 after the registration roller starts to convey the sheet, power is supplied to the fixing heater when the absolute value of the deviation Δθ is less than the threshold Δθth1. It is stopped and sheet conveyance is stopped, but not limited to this. For example, if the absolute value of the deviation Δθ is less than the threshold Δθth 1 and continues for a predetermined time after the sheet reaches a predetermined position upstream of the conveyance roller 318 b, the power supply to the fixing heater is stopped, and the sheet is conveyed May be stopped. The predetermined time is longer than the time it takes from when the sheet reaches the predetermined position to when the sheet reaches the nip portion of the conveyance roller 318 b. Further, for a predetermined time, a sheet of the distance obtained by adding the distance from the nip portion of registration roller 308 to the nip portion of fixing roller 318a and the circumferential length π * R of fixing roller 318a from the timing is conveyed The time is shorter than the time to

  The CPU 151a may have a function of the sheet detector 700 in the first embodiment and the second embodiment.

  In the first and second embodiments, the circumferential speed difference ΔV is set to a predetermined value regardless of the type (sheet type) of the sheet to be conveyed, but the present invention is not limited to this. For example, the peripheral speed difference ΔV may be set according to the paper type set by the user. The circumferential speed difference ΔV corresponding to thick paper may be smaller than the circumferential speed difference ΔV corresponding to thin paper and the circumferential speed difference ΔV corresponding to plain paper. Further, the circumferential speed difference ΔV corresponding to plain paper may be smaller than the circumferential speed difference ΔV corresponding to thin paper.

  In the first and second embodiments, the threshold Δθth of the deviation Δθ is a predetermined value regardless of the type of paper, but the threshold Δθth may be set for each type of paper.

  Further, in the first embodiment and the second embodiment, the time t0 at which the driving of the conveyance roller 318b is started is determined in advance by the operation sequence of the image forming apparatus 100, but the invention is not limited to this. For example, the drive of the conveyance roller 306 may be started based on the number of pulses output from the CPU 151a to the motor control device.

  In the first and second embodiments, the sheet is detected based on the deviation Δθ. However, the present invention is not limited to this. For example, the sheet may be detected based on a change in the current value iq output from the coordinate converter 511. Specifically, for example, when the current value iq becomes larger than the threshold iqth corresponding to the threshold Δθth, it may be determined that the leading end of the sheet has reached the nip portion of the transport roller 306. The sheet may be detected based on the change of the q-axis current command value (target value) iq_ref determined based on the deviation between the command phase θ_ref and the rotational phase θ determined by the phase determiner 513. . Alternatively, the sheet may be detected based on the change in the amplitude (size) of the current value iα or iβ of the stationary coordinate system.

  The current value iq, the current value iq_ref, and the amplitude of the current value iα or iβ of the stationary coordinate system correspond to parameters corresponding to the load torque applied to the rotor of the motor in the present invention.

  Further, in the first embodiment and the second embodiment, by controlling the rotational speed of the motor that drives the downstream conveying roller, the peripheral velocity of the downstream conveying roller differs from the circumferential velocity of the upstream conveying roller. Although it is attached, it is not this limitation. For example, by controlling the rotational speed of the motor that drives the upstream conveyance roller, the circumferential velocity of the downstream conveyance roller and the upstream conveyance roller may be differentiated. Further, by controlling the rotational speeds of both the motor for driving the upstream conveyance roller and the motor for driving the downstream conveyance roller, the peripheral speeds of the downstream conveyance roller and the upstream conveyance roller can be adjusted. It may be different.

  The application of the first and second embodiments is not limited to motor control by vector control. For example, the present embodiment is applied to a motor control device having a configuration for feeding back a rotational phase and a rotational speed.

  The photosensitive drum 309, the transfer charger 315, and the like in the first and second embodiments correspond to an image forming unit.

  In the first and second embodiments, the fixing roller 318a is used as a rotating body for fixing an image on a sheet by heat, but for example, a fixing belt may be used as a rotating body.

  In the first and second embodiments, a stepping motor is used as a motor for driving a load, but another motor such as a DC motor may be used. Further, the motor is not limited to the two-phase motor, and the first embodiment and the second embodiment can be applied to other motors such as a three-phase motor.

Further, in the vector control in the first embodiment and the second embodiment, the motor is controlled by performing phase feedback control, but the present invention is not limited to this. For example, the configuration may be such that the motor is controlled by feeding back the rotational speed ω of the rotor 402. Specifically, as shown in FIG. 12, speed determiner 514 is provided inside the motor control device, and speed determiner 514 rotates based on the amount of change in rotational phase θ output from phase determiner 513 in a predetermined period. Determine the velocity ω. In addition, the following Formula (10) shall be used for determination of speed.
ω = dθ / dt (10)

  Then, the CPU 151a outputs a commanded speed ω_ref representing a target speed of the rotor. Furthermore, a speed controller 500 is provided inside the motor controller, and the q-axis current command value iq_ref and the d-axis current command value id_ref are generated so that the speed controller 500 reduces the deviation between the rotational speed ω and the command speed ω_ref. Output. The motor may be controlled by performing such speed feedback control. In such a configuration, sheet detection is performed by the method described in the present embodiment, for example, based on the deviation Δω between the rotational speed ω and the command speed ω_ref. The commanded speed ω_ref is a target speed of the rotor of the motor M2 corresponding to the target speed of the circumferential speed of the conveyance roller 306.

  Further, in the first and second embodiments, permanent magnets are used as the rotor, but the present invention is not limited to this.

151a CPU
157 motor controller 309 photosensitive drum 315 transfer charger 318 fixing device 318a fixing roller 318b conveying roller 402 rotor 502 phase controller 513 phase determiner 700 sheet detector M1, M2 stepping motor

Claims (14)

Image forming means for forming an image on a sheet;
A fixing unit that includes a rotating body that supplies heat to a sheet, and fixes the image formed by the image forming unit to the sheet by the heat of the rotating body;
A transport roller that transports the sheet, the transport roller being adjacent to the rotating body and provided downstream of the rotating body in the transport direction in which the sheet is transported;
A motor for driving the transport roller;
Phase determining means for determining the rotational phase of the rotor of the motor;
Controlling a drive current flowing through a winding of the motor such that a deviation between a command phase representing a target phase of the rotor of the motor and a rotational phase of the rotor determined by the phase determination means is reduced Control means,
Second control means for controlling conveyance of the sheet;
Outputting means for outputting a predetermined signal when the absolute value of the value of the parameter corresponding to the load torque applied to the rotor of the motor exceeds a predetermined value;
Have
The distance from the nip of the rotor to the nip of the transport roller is shorter than the circumferential length of the rotor,
The second control means does not output the predetermined signal from the output means in a period from when the leading end of the sheet reaches a predetermined position upstream of the nip portion of the rotating body and until a predetermined time has elapsed In this case, the conveyance of the sheet is stopped. Image forming means for forming an image on a sheet;
A fixing unit that includes a rotating body that supplies heat to a sheet, and fixes the image formed by the image forming unit to the sheet by the heat of the rotating body;
A transport roller that transports the sheet, the transport roller being adjacent to the rotating body and provided downstream of the rotating body in the transport direction in which the sheet is transported;
A motor for driving the transport roller;
Speed determining means for determining the rotational speed of the rotor of the motor;
First control means for controlling a drive current flowing through a winding of the motor such that a deviation between a commanded speed representing a target speed of the rotor and the rotational speed of the rotor determined by the speed determining means is reduced When,
Second control means for controlling conveyance of the sheet;
Outputting means for outputting a predetermined signal when the absolute value of the value of the parameter corresponding to the load torque applied to the rotor of the motor exceeds a predetermined value;
Have
The distance from the nip of the rotor to the nip of the transport roller is shorter than the circumferential length of the rotor,
The control means controls a drive current flowing through a winding of the motor so that the rotating body and the conveyance roller rotate at different speeds.
In the second control means, the leading end of the sheet is the nip portion of the transport roller in a period from when the leading end of the sheet reaches a predetermined position upstream of the nip portion of the rotating body and until a predetermined time passes. An image forming apparatus that stops the conveyance of the sheet when a signal indicating that the sheet has arrived is not output from the output unit.   The image according to claim 1 or 2, wherein the control means controls a drive current flowing through a winding of the motor such that a peripheral velocity of the transport roller is higher than a peripheral velocity of the rotating body. Forming device. The image forming apparatus has a heater for heating the rotating body,
The second control means controls the supply of power to the heater,
The said 2nd control means stops supply of the electric power to the said heater, when the said predetermined | prescribed signal is not output from the said output means in the said period, It is described in any one of the Claims 1 thru | or 3 characterized by the above-mentioned. Image forming device.   The image according to any one of claims 1 to 4, wherein the second control means continues the conveyance of the sheet when the predetermined signal is output from the output means during the period. Forming device.   6. The image forming apparatus according to claim 1, further comprising: notification means for notifying that an abnormality has occurred in sheet conveyance when the predetermined signal is not output from the output means during the period. An image forming apparatus according to any one of the preceding claims.   The image forming apparatus according to any one of claims 1 to 6, wherein the rotating body is driven by a second motor different from the motor. The motor drives the conveyance roller and the rotating body,
The output means changes the value of the parameter corresponding to the load torque to the load torque after changing from a value smaller than a second predetermined value smaller than the predetermined value to a value larger than the second predetermined value. The said predetermined signal is output when the absolute value of the value of a corresponding parameter changes from a value smaller than the said predetermined value to a value larger than the said predetermined value, The said signal is output in any one of the Claims 1 thru | or 6 characterized by the above-mentioned. Image forming device.   The image forming apparatus according to any one of claims 1 to 8, wherein the rotating body is a fixing roller that fixes the image to the sheet by heat.   The image forming apparatus according to any one of claims 1 to 9, wherein the parameter corresponding to the load torque is the deviation. The image forming apparatus includes detection means for detecting a drive current flowing through the winding.
The control unit is configured to control the winding based on a torque current component that causes the rotor to generate torque, represented in a rotational coordinate system based on the rotational phase of the rotor determined by the phase determination unit. Control the flowing drive current,
The parameter corresponding to the load torque is a value of the torque current component of the drive current detected by the detection means, or any one of claims 3 to 9, wherein An image forming apparatus according to claim 1. The control unit is configured to control the winding based on a torque current component that causes the rotor to generate torque, represented in a rotational coordinate system based on the rotational phase of the rotor determined by the phase determination unit. Control the flowing drive current,
10. The image forming apparatus according to claim 1, wherein the parameter corresponding to the load torque is a target value of the torque current component. The image forming apparatus is
Phase determining means for determining the rotational phase of the rotor;
A detection unit that detects a drive current flowing through the winding;
The control unit is configured to control the winding based on a torque current component that causes the rotor to generate torque, represented in a rotational coordinate system based on the rotational phase of the rotor determined by the phase determination unit. Control the flowing drive current,
The parameter corresponding to the load torque is a value of the torque current component of the drive current detected by the detection means, or any one of claims 3 to 9, wherein An image forming apparatus according to claim 1. The image forming apparatus comprises phase determination means for determining the rotational phase of the rotor,
The control unit is configured to control the winding based on a torque current component that causes the rotor to generate torque, represented in a rotational coordinate system based on the rotational phase of the rotor determined by the phase determination unit. Control the flowing drive current,
The image forming apparatus according to any one of claims 3 to 9, wherein a parameter corresponding to the load torque is a target value of the torque current component.

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