Image formation device

Abstract

To deal with a possibility that control of a motor becomes unstable since load torque increases when the motor is accelerating and precise vector control is therefore failed, in a situation in which a gear provided in an axis of rotation of the motor and a gear provided in an axis of rotation of a second load engage with each other when the motor is accelerating when rotating in a second direction due to a backlash.SOLUTION: When a direction of previous rotation of a motor 509 and a direction of rotation indicated by information from a CPU 151a shows are different, a control system switches from constant current control to vector control when a rate of rotation ω_ref' reaches ω_tgt. Therefore, the control of the motor can be thus suppressed from becoming unstable.SELECTED DRAWING: Figure 7

Description

[Technical field]

[0001] The present invention relates to control of a motor in an image forming apparatus. [Background technology]

[0002] Conventionally, a control method called vector control is known as a method for controlling a motor by controlling a current value in a rotating coordinate system based on the rotation phase of the motor's rotor. Specifically, a control method is known in which a motor is controlled by performing phase feedback control, which controls a current value in the rotating coordinate system so as to reduce the deviation between a command phase of the rotor and the rotation phase. In addition, a control method is also known in which a motor is controlled by performing speed feedback control, which controls a current value in the rotating coordinate system so as to reduce the deviation between a command speed of the rotor and the rotation speed.

[0003] In vector control, the drive current flowing through the motor windings is represented by the q-axis component (torque current component), which is the current component that generates the torque to rotate the rotor, and the d-axis component (excitation current component), which is the current component that affects the strength of the magnetic flux that penetrates the motor windings. The torque required for rotation is generated efficiently by controlling the value of the torque current component according to changes in the load torque applied to the rotor. As a result, increases in motor noise and power consumption caused by surplus torque are suppressed.

[0004] Vector control requires a configuration for determining the rotation phase of the rotor. Patent Document 1 describes a configuration for determining the rotation phase of the rotor based on the induced voltage generated in the windings of each phase of the motor as the rotor rotates.

[0005] The magnitude of the induced voltage generated in the windings decreases as the rotation speed of the rotor decreases. If the magnitude of the induced voltage generated in the windings is not large enough to determine the rotation phase of the rotor, the rotation phase may not be determined with high accuracy. In other words, the lower the rotation speed of the rotor, the worse the accuracy of determining the rotation phase of the rotor may become.

[0006] Therefore, Patent Document 2 describes a configuration in which constant current control is used to control the motor by supplying a predetermined current to the motor windings when the command speed of the rotor is lower than a predetermined rotation speed. Note that in constant current control, neither phase feedback control nor speed feedback control is performed. Furthermore, Patent Document 2 describes a configuration in which vector control is used when the command speed of the rotor is equal to or higher than the predetermined rotation speed. That is, Patent Document 2 describes a configuration in which the control method for controlling the motor is switched from constant current control to vector control during the period in which the motor is accelerating.

[0007] Also, in the past, it has been known that in an image forming apparatus, when an image is formed on the second side of a recording medium having an image formed on its first side, the conveying roller is rotated in the reverse direction to convey the recording medium to a double-sided path (Patent Document 3). Specifically, the motor that rotates in the first direction to drive the conveying roller is stopped, and the motor is rotated in a second direction that is the opposite direction to the first direction, thereby rotating the conveying roller in the reverse direction. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Special Publication No. 2012-509056 [Patent Document 2] JP 2005-39955 A [Patent Document 3] JP 2020-201411 A Summary of the Invention [Problem to be solved by the invention]

[0009] When the motor rotating in the first direction is stopped, a gap (backlash) occurs between the gear provided on the rotating shaft of the motor and the gear provided on the rotating shaft of the second load. When the motor starts to rotate in the second direction in this state, the backlash causes the gear provided on the rotating shaft of the motor to mesh with the gear provided on the rotating shaft of the second load during the period when the motor rotating in the second direction is accelerating. In other words, during the period when the motor is accelerating, the load torque applied to the motor increases due to the meshing of the gear provided on the rotating shaft of the motor with the gear provided on the rotating shaft of the second load.

[0010] When the load torque increases, the rotation speed of the motor rotor decreases. For example, in the above-mentioned Patent Document 2, if the rotation speed of the motor rotor decreases immediately after the motor control method is switched from constant current control to vector control, it may not be possible to determine the rotation phase of the motor rotor with high accuracy. As a result, it may not be possible to perform high-accuracy vector control, and the motor control may become unstable.

[0011] In view of the above problems, an object of the present invention is to prevent the control of a motor from becoming unstable. [Means for solving the problem]

[0012] In order to solve the above problems, an image forming apparatus according to the present invention comprises: an image forming unit that forms an image on a sheet; a first conveying roller that rotates in a predetermined direction to convey the sheet having an image formed on a first surface by the image forming unit to a first conveying path, and then rotates in a direction opposite to the predetermined direction to invert the sheet and convey the sheet to a second conveying path; a second conveying roller that conveys the sheet conveyed to the second conveying path to the image forming unit; A motor that drives the first conveying roller; a gear train that transmits the driving force of the motor to the first conveying roller; A detection means for detecting a drive current flowing through a winding of the motor; a phase determining means for determining a rotation phase of a rotor of the motor based on the drive current detected by the detecting means; a control means including a first control mode for performing vector control to control a drive current flowing through a winding of the motor based on a torque current component, which is a current component expressed in a rotating coordinate system based on the rotation phase determined by the phase determination means and which generates a torque in the rotor, and a second control mode for controlling the drive current flowing through the winding based on a current of a predetermined magnitude; having the control means rotates the rotor in a first direction when rotating the transport roller in the predetermined direction, and rotates the rotor in a second direction that is the opposite direction to the first direction when rotating the transport roller in a direction opposite to the predetermined direction; the control means starts controlling the drive current in the second control mode, and thereafter, when a value corresponding to the rotation speed of the rotor reaches a predetermined speed, switches a control mode for controlling the drive current from the second control mode to the first control mode; The conveying roller conveys the sheet while being rotated by the motor driven at the predetermined speed in the first control mode. Effect of the Invention

[0013] According to the present invention, it is possible to prevent the control of the motor from becoming unstable. [Brief description of the drawings]

[0014] [Figure 1] 1 is a cross-sectional view illustrating an image forming apparatus according to a first embodiment. [Diagram 2] FIG. 2 is a block diagram showing a control configuration of the image forming apparatus. [Diagram 3]FIG. 2 is a diagram showing the relationship between a two-phase motor consisting of A-phase and B-phase, and a rotating coordinate system represented by the d-axis and q-axis. [Figure 4] 1 is a block diagram showing a configuration of a motor control device according to a first embodiment. [Diagram 5] FIG. 5 is a block diagram showing the configuration of a command generator 500. [Figure 6] FIG. 13 is a diagram showing an example of a method for performing a microstep driving method. [Figure 7] FIG. 4 is a diagram illustrating the timing for switching between vector control and constant current control. [Figure 8] FIG. 1 is a block diagram showing a configuration of a motor control device that performs speed feedback control. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] A preferred embodiment of the present invention will be described below with reference to the drawings. However, the shapes of the components and their relative positions described in the embodiment may be changed as appropriate depending on the configuration of the device to which the present invention is applied and various conditions, and the scope of the present invention is not intended to be limited to the following embodiment. In the following description, a case where the motor control device is provided in an image forming device will be described, but the device in which the motor control device is provided is not limited to an image forming device. For example, the motor control device may also be used in a sheet conveying device that conveys sheets such as recording media and original documents.

[0016] [First embodiment] [Image forming equipment] 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 device used in this embodiment. Note that the image forming apparatus is not limited to a copying machine, and may be, for example, a facsimile machine, a printing machine, a printer, etc. Furthermore, the recording method is not limited to an electrophotographic method, and may be, for example, an inkjet method, etc. Furthermore, the type of the image forming apparatus may be either a monochrome type or a color type.

[0017] The configuration and functions of the image forming apparatus 100 will be described below with reference to Fig. 1. As shown in Fig. 1, the image forming apparatus 100 includes an original reading device 200 and an image printing device 301.

[0018] <Document reader> The document reading device 200 is provided with a document feeding device 201 that feeds documents to a reading position. Documents P loaded on a document stacking section 2 of the document feeding device 201 are fed one by one by a pickup roller 3, and then transported by a paper feed roller 4. A separation roller 5 that is in pressure contact with the paper feed roller 4 is provided at a position opposite the paper feed roller 4. The separation roller 5 is configured to rotate when a load torque equal to or greater than a predetermined torque is applied to the separation roller 5, and has a function of separating documents that are fed in a two-sheet overlapping state.

[0019] The pickup roller 3 and the paper feed roller 4 are connected by a swing arm 12. The swing arm 12 is supported by the rotation shaft of the paper feed roller 4 so as to be rotatable around the rotation shaft of the paper feed roller 4.

[0020] The document P is transported by the paper feed roller 4 and the like, and is discharged to the paper discharge tray 10 by the paper discharge roller 11. As shown in Fig. 1, the document stacking section 2 is provided with a document set sensor SS1 that detects whether or not a document is stacked on the document stacking section 2. Also, the transport path through which the document passes is provided with a sheet sensor SS2 that detects the leading edge of the document (detects the presence or absence of the document).

[0021] The document reading device 201 is provided with a document reading section 16 that reads an image on a first side of a document being conveyed. Image information read by the document reading section 16 is output to an image printing device 301.

[0022] The document reading device 200 is also provided with a document reading unit 17 that reads an image on the second side of the document being conveyed. Image information read by the document reading unit 17 is output to the image printing device 301 in the same manner as described for the document reading unit 16.

[0023] In the manner described above, the document is read. That is, the document feeder 201 and the reader 202 function as a document reader.

[0024] Also, there are a first reading mode and a second reading mode as document reading modes. The first reading mode is a mode in which an image of a document transported by the above-mentioned method is read. The second reading mode is a mode in which an image of a document placed on the document glass 214 of the reading device 202 is read by the document reading unit 16 moving at a constant speed. Usually, an image of a sheet-like document is read in the first reading mode, and an image of a bound document such as a book or pamphlet is read in the second reading mode.

[0025] Inside the image printing device 301, sheet storage trays 302 and 304 are provided. Different types of recording media can be stored in the sheet storage trays 302 and 304. For example, A4 size plain paper is stored in the sheet storage tray 302, and A4 size thick paper is stored in the sheet storage tray 304. Note that the recording media refers to media on which an image is formed by the image forming device, and examples of the recording media include paper, resin sheets, cloth, overhead projector sheets, labels, etc.

[0026] The recording medium stored in the sheet storage tray 302 is fed by a paper feed roller 303, and is sent to the registration roller 308 by a transport roller 306. The recording medium stored in the sheet storage tray 304 is fed by a paper feed roller 305, and is sent to the registration roller 308 by transport rollers 307 and 306.

[0027] The image signal output from the document reading device 200 is input to an optical scanning device 311 including a semiconductor laser and a polygon mirror. In addition, the outer circumferential surface of a photosensitive drum 309 serving as a photoconductor is charged by a charger 310. After the outer circumferential surface of the photosensitive drum 309 is charged, a laser beam corresponding to the image signal input from the document reading device 200 to the optical scanning device 311 is irradiated onto the outer circumferential surface of the photosensitive drum 309 from the optical scanning device 311 via a polygon mirror and mirrors 312 and 313. As a result, an electrostatic latent image is formed on the outer circumferential surface of the photosensitive drum 309.

[0028] The developing device 314 as an image forming section has a developing roller 350 as a developer carrier. The electrostatic latent image formed on the outer peripheral surface of the photosensitive drum 309 is developed by the developer (toner) carried by the developing roller 350, 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 a recording medium by a transfer charger 315 as a transfer section provided at a position (transfer position) facing the photosensitive drum 309. In accordance with this transfer timing, the registration roller 308 sends the recording medium to the transfer position.

[0029] As described above, the recording medium onto which the toner image has been transferred is sent by the conveyor belt 317 to the fixing device 318 as an image forming section, and the toner image is fixed to the recording medium by heating and pressurizing the recording medium by the fixing device 318. In this manner, an image is formed on the recording medium by the image forming apparatus 100.

[0030] When an image is formed in a single-sided printing mode, the recording medium that has passed through the fixing device 318 is discharged to a discharge tray (not shown) by discharge rollers 319 and 324. When an image is formed in a double-sided printing mode, the recording medium is conveyed to a reversing path 325 by discharge rollers 319, conveying rollers 320, and reversing rollers 321 after a fixing process is performed on the first side of the recording medium by the fixing device 318. The recording medium is then reversed by the reversing rollers 321 and conveyed to a double-sided path 326. The recording medium conveyed to the double-sided path 326 is conveyed again to the registration rollers 308 by conveying rollers 323 and the like, and an image is formed on the second side of the recording medium by the method described above. The recording medium is then discharged to a discharge tray (not shown) by discharge rollers 319 and 324.

[0031] Furthermore, when the recording medium with an image formed on its first side is discharged face-down to the outside of image forming apparatus 100, the recording medium that has passed through fixing device 318 is conveyed through discharge rollers 319 toward conveying rollers 320. Thereafter, just before the rear end of the recording medium passes through the nip portion of conveying rollers 320, the rotation of conveying rollers 320 is reversed, and the recording medium is discharged to the outside of image forming apparatus 100 via discharge rollers 324 with the first side of the recording medium facing downward.

[0032] The configuration and functions of image forming apparatus 100 have been described above.

[0033] Fig. 2 is a block diagram showing an example of a control configuration of the image forming apparatus 100. As shown in Fig. 2, the system controller 151 includes a CPU 151a, a ROM 151b, and a RAM 151c. The system controller 151 is also connected to the image processing unit 112, an operation unit 152, an analog-digital (A / D) converter 153, a high voltage control unit 155, a motor control device 157, sensors 159, and an AC driver 160. The system controller 151 is capable of transmitting and receiving data and commands to and from each unit connected thereto.

[0034] The CPU 151a reads out and executes various programs stored in the ROM 151b to execute various sequences related to a predetermined image formation sequence.

[0035] RAM 151c is a storage device that stores various data such as set values ​​for high voltage control unit 155, command values ​​for motor control device 157, and information received from operation unit 152.

[0036] System controller 151 transmits setting value data of various devices provided inside image forming apparatus 100, which are necessary for image processing in image processing unit 112, to image processing unit 112. Furthermore, system controller 151 receives signals from sensors 159, and sets setting values ​​of high voltage control unit 155 based on the received signals.

[0037] The high voltage control unit 155 supplies a necessary voltage to the high voltage unit 156 (the charger 310, the developer 314, the transfer charger 315, etc.) in accordance with a set value set by the system controller 151. The sensors 159 include a sensor that detects the recording medium being transported by the transport roller.

[0038] The motor control device 157 controls a motor 509 that drives the reversing roller 321 in response to a command output from the CPU 151a. The driving force of the motor 509 is transmitted to the reversing roller 321 via a gear train (not shown). Although only the motor 509 is shown as the motor of the image forming apparatus in FIG. 2, a plurality of motors are actually provided in the image forming apparatus. Also, a configuration in which one motor control device controls a plurality of motors may be used. Furthermore, although only one motor control device is provided in FIG. 2, a plurality of motor control devices are actually provided in the image forming apparatus.

[0039] The A / D converter 153 receives a detection signal detected by a 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 for performing the fixing process. The fixing heater 161 is a heater used in the fixing process, and is included in the fixing unit 318.

[0040] The system controller 151 controls the operation unit 152 so that an operation screen for the user to set the type of recording medium to be used (hereinafter referred to as paper type) and the like is displayed on a display unit provided on the operation unit 152. The system controller 151 receives information set by the user from the operation unit 152, and controls the 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 status of the image forming apparatus to the operation unit 152. Note that the information indicating the status of the image forming apparatus is, for example, information regarding the number of images formed, the progress of the image forming operation, and sheet jams and multiple feeds in the document reading device 201 and the image printing device 301. The operation unit 152 displays the information received from the system controller 151 on the display unit.

[0041] As described above, the system controller 151 controls the operation sequence of the image forming apparatus 100 .

[0042] [Motor control device] Next, a motor control device according to the present embodiment will be described. The motor control device according to the present embodiment can control the motor using either of the vector control as the first control mode and the constant current control as the second control mode. In the following description, the following control is performed based on the rotation phase θ, the command phase θ_ref, and the current phase as electrical angles, but for example, the electrical angle may be converted to a mechanical angle and the following control may be performed based on the mechanical angle.

[0043] <Vector control> First, a method for vector control performed by motor control device 157 in this embodiment will be described with reference to Figures 3 and 4. Note that 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.

[0044] FIG. 3 is a diagram showing the relationship between a stepping motor (hereinafter referred to as a motor) 509 consisting of two phases, A phase (first phase) and B phase (second phase), and a rotating coordinate system represented by a d-axis and a q-axis. In FIG. 3, an α-axis corresponding to the A-phase winding and a β-axis corresponding to the B-phase winding are defined in a stationary coordinate system. In FIG. 3, a d-axis is defined along the direction of the magnetic flux created by the magnetic poles of the permanent magnet used in the rotor 402, and a q-axis is defined along a direction 90 degrees counterclockwise from the d-axis (direction perpendicular to the d-axis). The angle between the α-axis and the d-axis is defined as θ, and the rotation phase of the rotor 402 is represented by the angle θ. In vector control, a rotating coordinate system based on the rotation phase θ of the rotor 402 is used. Specifically, vector control uses the current components in a rotating coordinate system of a current vector corresponding to the drive current flowing through the windings, including the q-axis component (torque current component) that generates torque in the rotor and the d-axis component (excitation current component) that affects the strength of the magnetic flux penetrating the windings.

[0045] Vector control is a control method for controlling a motor by performing phase feedback control to control the values ​​of torque current components and excitation current components so as to reduce the deviation between a command phase representing a target phase of the rotor and the actual rotation phase. There is also a method for controlling a motor by performing speed feedback control to control the values ​​of torque current components and excitation current components so as to reduce the deviation between a command speed representing a target speed of the rotor and the actual rotation speed.

[0046] 4 is a block diagram showing an example of the configuration of the motor control device 157 that controls the motor 509. The motor control device 157 is configured with at least one ASIC, and executes each function described below.

[0047] As shown in FIG. 4, the motor control device 157 has a constant current controller 517 that performs constant current control, and a vector controller 518 that performs vector control.

[0048] The motor control device 157 includes, as circuits for vector control, a phase controller 502, a current controller 503, a coordinate inverse converter 505, a coordinate converter 511, a PWM inverter 506 for supplying a drive current to the windings of the motor, and the like. The coordinate converter 511 converts the current vector corresponding to the drive current flowing through the A-phase and B-phase windings of the motor 509 from a stationary coordinate system represented by the α-axis and β-axis to a rotating coordinate system represented by the q-axis and d-axis. As a result, the drive current flowing through the windings is represented by a current value of a q-axis component (q-axis current) and a current value of a d-axis component (d-axis current), which are current values ​​in the rotating coordinate system. The q-axis current corresponds to a torque current that generates a torque in the rotor 402 of the motor 509. The d-axis current corresponds to an excitation current that affects the strength of the magnetic flux that penetrates the windings of the motor 509. The motor control device 157 can control the q-axis current and the d-axis current independently. As a result, the motor control device 157 can efficiently generate the torque required for rotating the rotor 402 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.

[0049] The motor control device 157 determines the rotation phase θ of the rotor 402 of the motor 509 by a method described later, and performs vector control based on the result. The CPU 151a outputs a drive pulse to the command generator 500 as a command to drive the motor based on the operation sequence of the motor 509. Note that the operation sequence of the motor (motor drive pattern) is stored in, for example, ROM 151b, and the CPU 151a outputs the drive pulse based on the operation sequence stored in ROM 151b.

[0050] The command generator 500 generates and outputs a command phase θ_ref representing a target phase of the rotor 402, based on a driving pulse output from the CPU 151a. The configuration of the command generator 500 will be described later.

[0051] The subtractor 101 calculates and outputs the deviation between the rotational phase θ of the rotor 402 of the motor 509 and the command phase θ_ref.

[0052] The phase controller 502 acquires the deviation Δθ at a period T (for example, 200 μs). The phase controller 502 generates and outputs a q-axis current command value iq_ref and a d-axis current command value id_ref based on proportional control (P), integral control (I), and differential control (D) so that the deviation Δθ acquired from the subtractor 101 becomes small. Specifically, the phase controller 502 generates and outputs a q-axis current command value iq_ref and a d-axis current command value id_ref based on the P control, I control, and D control so that the deviation Δθ acquired from the subtractor 101 becomes zero. The P control is a control method in which the value of the object to be controlled is controlled based on a value proportional to the deviation between a command value and an estimated value. The I control is a control method in which the value of the object to be controlled is controlled based on a value proportional to the time integral of the deviation between a command value and an estimated value. D control is a control method for controlling the value of a controlled object based on a value proportional to the time change of the deviation between a command value and an estimated value. In this embodiment, the phase controller 502 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. In this embodiment, the d-axis current command value id_ref, which affects the strength of the magnetic flux penetrating the winding, is set to 0, but is not limited to this.

[0053] The drive current flowing through the A-phase winding of motor 509 is detected by current detector 507 and then converted from an analog value to a digital value by A / D converter 510. The drive current flowing through the B-phase winding of motor 509 is detected by current detector 508 and then converted from an analog value to a digital value by A / D converter 510. The cycle in which current detectors 507 and 508 detect the current is, for example, equal to or shorter than the cycle T in which phase controller 502 acquires deviation Δθ (for example, 25 μs).

[0054] The current value of the drive current converted from an analog value to a digital value by the A / D converter 510 is expressed as the current values ​​iα and iβ in the stationary coordinate system by the following equation using the phase θe of the current vector shown in Fig. 3. 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.

[0055] iα=I*cosθe (1) iβ=I*sinθe (2) These current values ​​iα and iβ are input to a coordinate converter 511 and an induced voltage determiner 512 .

[0056] The coordinate converter 511 converts the current values ​​iα and iβ in the stationary coordinate system into a current value iq of the q-axis current and a current value id of the d-axis current in the rotating coordinate system by the following equation.

[0057] id = cosθ*iα + sinθ*iβ (3) iq = -sinθ*iα+cosθ*iβ (4) The coordinate converter 511 outputs the converted current value iq to the subtractor 102. The coordinate converter 511 also outputs the converted current value id to the subtractor 103.

[0058] The subtractor 102 calculates the deviation between the q-axis current command value iq_ref and the current value iq, and outputs the deviation to the current controller 503 .

[0059] Further, the subtractor 103 calculates the deviation between the d-axis current command value id_ref and the current value id, and outputs the deviation to the current controller 503 .

[0060] The current controller 503 generates the drive voltages Vq and Vd based on PID control so that the input deviations are each reduced. Specifically, the current controller 503 generates the drive voltages Vq and Vd so that the input deviations are each reduced to zero, and outputs the drive voltages to the coordinate inverse converter 505. Note that, although the current controller 503 in this 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.

[0061] The coordinate inverse converter 505 inversely converts the drive voltages Vq and Vd in the rotating coordinate system output from the current controller 503 into drive voltages Vα and Vβ in the stationary coordinate system by the following equations.

[0062] Vα=cosθ*Vd-sinθ*Vq (5) Vβ=sinθ*Vd+cosθ*Vq (6) The coordinate inverse converter 505 outputs the inversely converted drive voltages Vα and Vβ to the induced voltage determiner 512 and the PWM inverter 506 .

[0063] The PWM inverter 506 has a full-bridge circuit. The full-bridge circuit is driven by a PWM (pulse width modulation) 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 supplies the drive currents iα and iβ to windings of each phase of the motor 509, thereby driving the motor 509. Note that, although the PWM inverter has a full-bridge circuit in this embodiment, the PWM inverter may be a half-bridge circuit or the like.

[0064] Next, a configuration for determining the rotation phase θ will be described. The rotation phase θ of the rotor 402 is determined using the values ​​of induced voltages Eα and Eβ induced in the A-phase and B-phase windings of the motor 509 by the rotation of the rotor 402. The values ​​of the induced voltages are determined (calculated) by an induced voltage determiner 512. Specifically, the induced voltages Eα and Eβ are determined by the following equations from the current values ​​iα and iβ input from the A / D converter 510 to the induced voltage determiner 512 and the drive voltages Vα and Vβ input from the coordinate inverse converter 505 to the induced voltage determiner 512.

[0065] Eα=Vα-R*iα-L*diα / dt (7) Eβ=Vβ-R*iβ-L*diβ / dt (8) Here, R is the winding resistance, and L is the winding inductance. The values ​​of the winding resistance R and the winding inductance L are specific to the motor 509 being used, and are stored in advance in the ROM 151b or a memory (not shown) provided in the motor control device 157.

[0066] The induced voltages Eα and Eβ determined by the induced voltage determiner 512 are output to a phase determiner 513 .

[0067] The phase determiner 513 determines the rotational phase θ of the rotor 402 of the motor 509 based on the ratio between the induced voltages Eα and Eβ output from the induced voltage determiner 512, using the following equation.

[0068] θ=tan^-1(-Eβ / Eα) (9) In this embodiment, the phase determiner 513 determines the rotation phase θ by performing a calculation based on the formula (9), but this is not limiting. For example, the phase determiner 513 may determine the rotation phase θ by referring to a table stored in the ROM 151b or the like that indicates the relationship between the induced voltages Eα and Eβ and the rotation phase θ corresponding to the induced voltages Eα and Eβ.

[0069] The rotation phase θ of the rotor 402 obtained as described above is input to the subtractor 101 , the coordinate inverse converter 505 , and the coordinate converter 511 .

[0070] When vector control is performed, the motor control device 157 repeats the above-mentioned control.

[0071] As described above, the motor control device 157 in this embodiment performs vector control using phase feedback control that controls the current value in the rotating coordinate system so as to reduce the deviation between the command phase θ_ref and the rotational phase θ. By performing vector control, it is possible to prevent the motor from going out of step, and to prevent an increase in motor noise and power consumption due to surplus torque.

[0072] <Constant current control> Next, the constant current control in this embodiment will be described.

[0073] In constant current control, a predetermined current is supplied to the windings of the motor to control the drive current flowing through the windings. Specifically, in constant current control, a drive current having a magnitude (amplitude) corresponding to a torque obtained by adding a predetermined margin to the torque assumed to be necessary for the rotor to rotate is supplied to the windings so that the motor does not lose step-out even if the load torque applied to the rotor fluctuates. This is because constant current control does not use a configuration in which the magnitude of the drive current is controlled based on a determined (estimated) rotation phase or rotation speed (feedback control is not performed), and therefore the drive current cannot be adjusted according to the load torque applied to the rotor. Note that the larger the magnitude of the current, the greater the torque applied to the rotor. Also, the amplitude corresponds to the magnitude of the current vector.

[0074] In the following description, during constant current control, the motor is controlled by supplying a current of a predetermined magnitude to the motor windings; however, for example, during constant current control, the motor may be controlled by supplying a current of a predetermined magnitude to the motor windings depending on whether the motor is accelerating or decelerating.

[0075] 4, a command generator 500 outputs a command phase θ_ref to a constant current controller 517 based on a drive pulse output from a CPU 151a. The constant current controller 517 generates and outputs current command values ​​iα_ref and iβ_ref in a stationary coordinate system corresponding to the command phase θ_ref output from the command generator 500. In this embodiment, the magnitude of a current vector corresponding to the current command values ​​iα_ref and iβ_ref in a stationary coordinate system is always constant.

[0076] Drive currents flowing through A-phase and B-phase windings of motor 509 are detected by current detectors 507 and 508. The detected drive currents are converted from analog values ​​to digital values ​​by A / D converter 510, as described above.

[0077] The subtractor 102 receives the current value iα output from the A / D converter 510 and the current command value iα_ref output from the constant current controller 517. The subtractor 102 calculates the deviation between the current command value iα_ref and the current value iα, and outputs the deviation to the current controller 503.

[0078] Further, the subtractor 103 receives the current value iβ output from the A / D converter 510 and the current command value iβ_ref output from the constant current controller 517. The subtractor 103 calculates the deviation between the current command value iβ_ref and the current value iβ, and outputs the deviation to the current controller 503.

[0079] The current controller 503 outputs the drive voltages Vα and Vβ based on the PID control so that the input deviation becomes small. Specifically, the current controller 503 outputs the drive voltages Vα and Vβ so that the input deviation approaches zero.

[0080] The PWM inverter 506 supplies drive currents to the windings of each phase of the motor 509 based on the input drive voltages Vα and Vβ in the manner described above, thereby driving the motor 509 .

[0081] As described above, in the constant current control of this embodiment, neither phase feedback control nor speed feedback control is performed. That is, in the constant current control of this embodiment, the drive current supplied to the windings is not adjusted according to the rotation state of the rotor. Therefore, in the constant current control, a current obtained by adding a predetermined margin to the current required to rotate the rotor is supplied to the windings so that the motor does not go out of step.

[0082] <Command generator> Fig. 5 is a block diagram showing the configuration of a command generator 500 in this embodiment. As shown in Fig. 5, the command generator 500 has a speed generator 500a that generates a rotation speed ω_ref' in place of a command speed based on a drive pulse output from the CPU 151a, and a command value generator 500b that generates a command phase θ_ref based on the drive pulse.

[0083] The speed generator 500a generates a rotation speed ω_ref' based on the time interval between the falling edges of successive drive pulses, and outputs the rotation speed ω_ref' to a control switcher 515, which will be described later. The rotation speed ω_ref' changes with a period corresponding to the period of the drive pulse.

[0084] The command value generator 500b generates and outputs a command phase θ_ref according to the following equation (10) based on the drive pulse output from the CPU 151a.

[0085] θ_ref=θini+θstep*n (10) Here, θini is the phase (initial phase) of the rotor when the motor starts to drive, θstep is the increment (amount of change) of θ_ref per drive pulse, and n is the number of pulses input to the command value generator 500b.

[0086] {Microstep drive method} In this embodiment, a microstep driving method is used in the constant current control. Note that the driving method used in the constant current control is not limited to the microstep driving method, and may be, for example, a full step driving method or other driving method.

[0087] Fig. 6 is a diagram showing an example of a method for performing the microstep driving method, in which a driving pulse output from a CPU 151a, a command phase θ_ref generated by a command value generator 500b, and currents flowing through the A-phase and B-phase windings are shown.

[0088] A method of performing microstep driving in this embodiment will be described below with reference to Figures 5 and 6. Note that the driving pulse and command phase shown in Figure 6 show a state in which the rotor rotates at a constant speed.

[0089] The lead of the command phase θ_ref in the microstep drive method is 90°, which is the lead of the command phase θ_ref in the full-step drive method, divided by 1 / N (N is a positive integer), resulting in a current waveform that smoothly changes to a sine wave as shown in Figure 6, allowing for more precise control of the rotor rotation phase θ.

[0090] When micro-step driving is performed, the command value generator 500b generates and outputs a command phase θ_ref according to the following equation (11) based on the driving pulse output from the CPU 151a.

[0091] θ_ref=45°+90 / N°*n (11) In this way, when one drive pulse is input, the command value generator 500b updates the command phase θ_ref by adding 90 / N° to the command phase θ_ref. That is, the number of drive pulses output from the CPU 151a corresponds to the command phase. The period (frequency) of the drive pulses output from the CPU 151a corresponds to the target speed (command speed) of the rotor of the motor 509.

[0092] <Switching between vector control and constant current control> Next, switching between vector control and constant current control in this embodiment will be described. In this embodiment, the following configuration is applied to prevent the motor control from becoming unstable.

[0093] As shown in Fig. 4, the motor control device 157 in this embodiment has a configuration for switching between constant current control and vector control. Specifically, the motor control device 157 has a control switch 515 and switches 516a, 516b, and 516c. During the period in which the constant current control is being performed, the induced voltage determiner 512, the phase determiner 513, and the coordinate converter 519 may be operating. During the period in which the vector control is being performed, the circuit that performs the constant current control may be operating.

[0094] The control switch 515 sets the switching signal to 'L' when constant current control is performed, and sets the switching signal to 'H' when vector control is performed. The switching signal is input to switches 516a, 516b, and 516c as shown in Fig. 4. Note that the control switch 515 outputs the switching signal, for example, at the same cycle as the cycle T at which the CPU 151a outputs the rotation speed ω_ref'.

[0095] In this embodiment, when rotating the motor 509, the CPU 151a outputs information indicating whether to rotate the motor 509 in a first direction or in a second direction opposite to the first direction to the motor control device 157. The control switch 515 stores the information in the memory 515a.

[0096] The control switch 515 determines the timing (switching timing) for switching between the vector control and the constant current control based on the previous rotation direction of the motor 509 stored in the memory 515a and the information on the rotation direction output from the CPU 151a. After determining the timing, the control switch 515 overwrites the information on the rotation direction output from the CPU 151a in the memory 515a.

[0097] Fig. 7 is a diagram for explaining the timing of switching between vector control and constant current control. Fig. 7(a) is a diagram showing the switching timing when the control switch 515 switches between the previous rotation direction of the motor 509 stored in the memory 515a and the rotation direction indicated by the information output from the CPU 151a, and Fig. 7(b) is a diagram showing the switching timing when the control switch 515 switches between the previous rotation direction of the motor 509 stored in the memory 515a and the rotation direction indicated by the information output from the CPU 151a, and the rotation direction is different.

[0098] 7(a), an increase in load torque caused by backlash between the gear provided on the rotating shaft of the motor 509 and the gear provided on the rotating shaft of the reverse roller 321 does not occur during acceleration of the motor 509. Therefore, in this embodiment, when the previous rotation direction of the motor 509 stored in the memory 515a and the rotation direction indicated by the information output from the CPU 151a are the same direction, the control switcher 515 switches the control method as follows.

[0099] Specifically, when the rotation speed ω_ref' is equal to or greater than the threshold value ωth (ω_ref'≧ωth), the control switch 515 outputs a switching signal = 'H'. On the other hand, when the rotation speed ω_ref' is less than the threshold value ωth (ω_ref'<ωth), the control switch 515 outputs a switching signal = 'L'. Note that the threshold value ωth in this embodiment is set to a value greater than the smallest rotation speed ω_min among the rotation speeds at which the rotation phase θ is determined with high precision. That is, in vector control, the rotation phase θ is determined with high precision. Also in constant current control, if the rotation speed of the motor rotor is equal to or greater than ω_min, the rotation phase θ is determined with high precision.

[0100] 7(b), an increase in load torque occurs during acceleration of the motor 509 due to backlash between a gear provided on the rotation shaft of the motor 509 and a gear provided on the rotation shaft of the reverse roller 321. Therefore, in this embodiment, when the previous rotation direction of the motor 509 stored in the memory 515a differs from the rotation direction indicated by the information output from the CPU 151a, the control switcher 515 switches the control method as follows.

[0101] Specifically, when the rotation speed ω_ref' reaches the rotation speed ω_tgt while the constant current control is being executed, the control switch 515 switches the switching signal from 'L' to 'H'. The rotation speed ω_tgt corresponds to the rotation speed of the motor 509 when the reversing roller 321 conveys the recording medium. In other words, the motor 509 drives the reversing roller 321 while the rotation speed is ω_tgt as a predetermined speed.

[0102] On the other hand, when the rotation speed ω_ref′ becomes smaller than the threshold value ωth in a state in which the vector control is being executed, the control switch 515 switches the switching signal from 'H' to 'L'.

[0103] As described above, in this embodiment, if the previous rotation direction of the motor 509 is different from the rotation direction indicated by the information output from the CPU 151a, when the rotation speed ω_ref' reaches ω_tgt, the control method is switched from constant current control to vector control. As a result, it is possible to prevent the motor control from becoming unstable.

[0104] Furthermore, in this embodiment, if the previous rotation direction of the motor 509 is the same as the rotation direction indicated by the information output from the CPU 151a, the control method is switched from constant current control to vector control when the rotation speed ω_ref' becomes equal to or greater than ωth. As a result, the period during which vector control is executed can be made as long as possible compared to when the rotation direction indicated by the information output from the CPU 151a is different. In other words, power consumption in driving the motor can be suppressed.

[0105] In addition, in this embodiment, when the rotation speed ω_ref' becomes smaller than the threshold value ωth while the vector control is being executed, the control method is switched from the vector control to the constant current control. As a result, the period during which the vector control is executed can be extended as long as possible. In other words, the power consumption during the drive of the motor can be suppressed.

[0106] In this embodiment, when the previous rotation direction of the motor 509 is different from the rotation direction indicated by the information output from the CPU 151a, the control method is switched from the constant current control to the vector control when the rotation speed ω_ref' reaches ω_tgt, but this is not limited to the above. For example, when the previous rotation direction of the motor 509 is different from the rotation direction indicated by the information output from the CPU 151a, the control method may be switched from the constant current control to the vector control a predetermined time after the motor 509 is started. The predetermined time is a time longer than the time from the start of the motor 509 until an increase in the load torque due to backlash occurs, and is a time determined in advance by an experiment or the like.

[0107] For a motor that drives a load that rotates in only one direction, such as the conveying roller 307, a configuration may be applied in which the control method switches from constant current control to vector control when the rotation speed ω_ref′ becomes equal to or greater than ωth.

[0108] In this embodiment, the configuration for switching the control method of the motor that drives the reversing roller 321 has been described, but the configuration for switching the control method in this embodiment is not limited to being applied to the reversing roller 321. For example, it is also applied to the conveying roller 320 and the like.

[0109] In the vector control of this embodiment, the motor 509 is controlled by performing phase feedback control, but the present invention is not limited to this. For example, the motor 509 may be controlled by feeding back the rotation speed ω of the rotor 402. Specifically, as shown in FIG. 8, the CPU 151a outputs a command speed ω_ref representing a target speed of the rotor. Furthermore, a speed determiner 514 provided inside the motor control device determines the rotation speed ω based on the time change of the rotation phase θ output from the phase determiner 513. The following equation (12) is used to determine the speed.

[0110] ω=dθ / dt (12) The speed controller 600 is configured to generate and output the q-axis current command value iq_ref so that the deviation between the rotation speed ω and the command speed ω_ref becomes small. The motor 509 may be controlled by performing such speed feedback control. In such a configuration, since the rotation speed is fed back, the rotation speed of the rotor can be controlled to a predetermined speed.

[0111] In the motor control device of this embodiment, the circuit performing vector control and the circuit performing constant current control share some parts (current controllers 503, 504, PWM inverter 506, etc.), but this is not limited to this. For example, the circuit performing vector control and the circuit performing constant current control may be provided independently.

[0112] In addition, the rotation speed ω_ref' may be determined based on the period in which the magnitude of a periodic signal correlated with the rotation period of the rotor 402, such as the drive current iα or iβ, the drive voltage Vα or Vβ, or the induced voltage Eα or Eβ, becomes 0.

[0113] In addition, in this embodiment, a stepping motor is used as the motor that drives the load, but other motors such as a DC motor, a brushless DC motor, etc. may be used. Furthermore, the motor is not limited to a two-phase motor, and this embodiment can be applied to other motors such as a three-phase motor.

[0114] In addition, in this embodiment, a permanent magnet is used as the rotor, but the present invention is not limited to this. [Explanation of symbols]

[0115] 157 Motor control device 318 Fixing unit 321 Reversing roller 322 Transport roller 325 Reverse Pass 326 Double-sided pass 402 Rotor 502 Phase Controller 507,508 Current detector 509 Motor 513 Phase determiner 517 Constant Current Controller 518 Vector Controller

Claims

1. An image forming unit that forms an image on a sheet; A conveyance roller that rotates the sheet on which an image is formed on the first surface by the image forming unit in a predetermined direction and conveys it to a first conveyance path, and then reverses the front and back of the sheet by rotating in a direction opposite to the predetermined direction and conveys the sheet to a second conveyance path; A motor that drives the conveyance roller; A gear train that transmits the driving force of the motor to the first conveyance roller; Detection means for detecting a drive current flowing through the winding of the motor; Phase determination means for determining the rotational phase of the rotor of the motor based on the drive current detected by the detection means; A first control mode that performs vector control for controlling the drive current flowing through the winding of the motor based on a torque current component, which is a current component represented in a rotational coordinate system with the rotational phase determined by the phase determination means as a reference and which generates torque in the rotor, and a second control mode that controls the drive current flowing through the winding based on a current having a predetermined magnitude, and control means; having; The control means rotates the conveyance roller in the predetermined direction by rotating the rotor in a first direction, and rotates the conveyance roller in a direction opposite to the predetermined direction by rotating the rotor in a second direction, which is opposite to the first direction. The control means starts controlling the drive current in the second control mode, and then, when a value corresponding to the rotational speed of the rotor reaches a predetermined speed, switches the control mode for controlling the drive current from the second control mode to the first control mode. The predetermined speed is a speed corresponding to the speed at which the conveyance roller conveys the sheet, and is a constant value. An image forming apparatus characterized by this.

2. The image forming apparatus according to claim 1, wherein the control means switches the control mode from the first control mode to the second control mode when a value corresponding to the rotation speed of the rotor becomes smaller than a second predetermined speed that is smaller than the predetermined speed in a state where the drive current is controlled by the first control mode.

3. An image forming unit that forms an image on a sheet, a conveyance roller that rotates a sheet having an image formed on a first surface by the image forming unit in a predetermined direction and conveys the sheet to a first conveyance path, and then reverses the front and back of the sheet by rotating in a direction opposite to the predetermined direction and conveys the sheet to a second conveyance path, a motor that drives the conveyance roller, a gear train that transmits the driving force of the motor to the first conveyance roller, detection means for detecting a drive current flowing through the winding of the motor, phase determination means for determining the rotation phase of the rotor of the motor based on the drive current detected by the detection means, a first control mode for performing vector control to control the drive current flowing through the winding of the motor based on a current component that is a current component represented in a rotation coordinate system with the rotation phase determined by the phase determination means as a reference and that generates torque in the rotor; and a second control mode for controlling the drive current flowing through the winding based on a current having a predetermined magnitude, and control means including the second control mode, having the control means rotates the conveyance roller in the predetermined direction by rotating the rotor in a first direction, and rotates the conveyance roller in a direction opposite to the predetermined direction by rotating the rotor in a second direction that is opposite to the first direction, When the conveyance roller rotates in the predetermined direction, the control means starts controlling the drive current in the second control mode, and then, when the value corresponding to the rotation speed of the rotor reaches a first predetermined speed, the control mode for controlling the drive current is switched from the second control mode to the first control mode. When the conveyance roller rotates in the reverse direction, the control means starts controlling the drive current in the second control mode, and then, when the value corresponding to the rotation speed of the rotor reaches a second predetermined speed higher than the first predetermined speed, the control mode for controlling the drive current is switched from the second control mode to the first control mode. An image forming apparatus characterized by this.

4. In any of the states where the control means is controlling the drive current in the first control mode while the conveyance roller is rotating in the predetermined direction and where the control means is controlling the drive current in the first control mode while the conveyance roller is rotating in the reverse direction, when the value corresponding to the rotation speed of the rotor becomes smaller than the first predetermined speed, the control mode is switched from the first control mode to the second control mode. The image forming apparatus according to claim 3, characterized by this.

5. The first control mode is a control mode for controlling the drive current based on the torque current component so that the deviation between the rotation phase determined by the phase determination means and the command phase representing the target phase of the rotor becomes small. The image forming apparatus according to claim 1 or 3, characterized by this.

6. The image forming apparatus has speed determination means for determining the rotation speed of the rotor. The first control mode is a control mode for controlling the drive current based on the torque current component so that the deviation between the rotation speed determined by the speed determination means and the command speed representing the target speed of the rotor becomes small. The image forming apparatus according to claim 1 or 3, characterized by this.

7. The conveyance roller conveys the sheet in the direction of discharging the sheet from the image forming apparatus by rotating in the reverse direction. The image forming apparatus according to claim 1 or 3, characterized by this.

8. The image forming apparatus according to claim 1 or 3, wherein the conveyance roller conveys the sheet to the image forming unit so as to form an image on the second surface of the sheet by rotating in the reverse direction.

Images