Sheet conveying device and image forming apparatus

Abstract

To solve the problem in which: due to stoppage of a motor after a control method for the motor is switched from vector control to constant current control, the distance between a rotation shaft of a first rotating body and a rotation shaft of a second rotating body may not be accurately adjusted; as a result of that, an image may not be appropriately formed on a recording medium.SOLUTION: A motor drives a conveying roller that conveys a recording medium and the drive of the motor is started through constant current control, and subsequently a control mode is switched from the constant current control to vector control. That is, the recording medium is conveyed by the conveying roller driven by the motor controlled through the vector control. A stepping motor 403 is controlled through the constant current control in a period from the start to stop.SELECTED DRAWING: Figure 5

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 to control a current value in the rotating coordinate system so as to reduce the deviation between a command phase and the rotation phase of the rotor.

[0003] In vector control, the drive current flowing through the motor windings is represented by a q-axis component (torque current component), which is a current component that generates the torque for rotating the rotor, and a d-axis component (excitation current component), which is a current component that affects the strength of the magnetic flux that penetrates the motor windings. The value of the torque current component is controlled according to changes in the load torque applied to the rotor, so that the torque required for rotation is generated efficiently. As a result, increases in motor noise and power consumption caused by excess torque are suppressed. It is also possible to suppress the rotor from becoming out of synchronization with the input signal due to the load torque applied to the rotor exceeding the output torque corresponding to the drive current supplied to the motor windings, causing the motor to enter an uncontrollable state (out-of-step state).

[0004] Patent Document 1 describes a method of reducing power consumption in an image forming apparatus by controlling a stepping motor (hereinafter, referred to as a motor) that drives a load provided in the image forming apparatus through vector control. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2017-189091 A Summary of the Invention [Problem to be solved by the invention]

[0006] The above-mentioned Patent Document 1 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. The above-mentioned Patent Document 1 further 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, in the configuration of the above-mentioned Patent Document 1, the motor controlled by vector control is stopped after the control method of the motor is switched from vector control to constant current control.

[0007] FIG. 10 is a diagram showing an example of the relationship between the command speed ω_ref, which indicates the target speed of the rotor of the motor, and the actual rotation speed ω of the rotor of the motor. In FIG. 10, the dashed line indicates the command speed ω_ref, and the solid line indicates the rotation speed ω. In FIG. 10, the dashed line and the solid line are shown overlapping each other in the period from when the motor starts to be driven to when the motor starts to decelerate, and in the period from when the command speed ω_ref becomes equal to or less than the threshold value ωth to when the motor is stopped. Note that the waveform of the command speed ω_ref and the number of drive pulses output from a host device such as a CPU from when the motor starts to be driven to when it is stopped are preset, for example, based on the drive sequence of the motor. That is, the number of drive pulses output from a host device from when the control of the motor is switched from vector control to constant current control to when the motor is stopped is preset.

[0008] As shown in Fig. 10, when the command speed ω_ref decreases, the rotation speed ω does not immediately follow the command speed ω_ref, but becomes a value larger than the command speed ω_ref. In other words, the rotation phase of the rotor becomes a phase that leads the target phase of the rotor. This is because the rotor rotating at a constant speed tries to maintain rotation at the constant speed due to inertia.

[0009] For example, when the command speed ω_ref is decreased while vector control is being performed, the motor control device that controls the motor detects that the rotation phase of the rotor is ahead of the target phase, and then controls the drive current so that the rotation phase becomes the target phase. As a result, the rotation phase may end up leading the target phase by one electrical revolution or more due to a control delay. When the motor control is switched from vector control to constant current control in a state where the rotation phase leads the target phase by one electrical revolution or more, the rotation phase when the rotor stops may end up leading the phase at which the rotor should be stopped. In other words, the rotation phase of the rotor that should be stopped may differ from the actual stop phase of the rotor.

[0010] In the image forming apparatus, a cam for bringing a photosensitive drum carrying a toner image into contact with and away from a transfer roller for transferring the toner image formed on the photosensitive drum to a transfer belt is driven by a motor. In addition, in the image forming apparatus, a cam for bringing a fixing roller for fixing a toner image on a recording medium into contact with and away from a pressure roller for forming a nip portion together with the fixing roller is driven by a motor. When the control method described in the above-mentioned Patent Document 1 is applied to the control of a motor for driving a cam for adjusting the distance between the rotation axis of the first rotating body and the rotation axis of the second rotating body (bringing the first rotating body into contact with and away from the second rotating body), the following problems may occur. Specifically, the motor may be stopped after the motor control method is switched from vector control to constant current control, and therefore the distance between the rotation axis of the first rotating body and the rotation axis of the second rotating body may not be adjusted with high accuracy. If the distance between the rotation axis of the first rotating body and the rotation axis of the second rotating body is not adjusted with high accuracy, an image may not be formed appropriately on a recording medium.

[0011] In view of the above problems, an object of the present invention is to drive a motor using an appropriate control method according to the function of a load driven by the motor while suppressing power consumption in a sheet transport device. [Means for solving the problem]

[0012] In order to solve the above problems, a sheet conveying device according to the present invention comprises: A first rotating body; A second rotor that rotates while forming a nip portion with the first rotor; a moving means for moving the first rotating body so as to adjust a distance between the first rotating body and the second rotating body; A conveying roller for conveying a sheet; A first motor that drives the conveying roller; A second motor for driving the moving means; a phase determining means for determining a rotational phase of a rotor of the first motor; a control means for executing control including a first control mode for controlling the motor based on a current of a predetermined magnitude and a second control mode for controlling the motor based on the rotation phase determined by the phase determination means; Equipped with The control means controls the first motor. First Control a control mode for the first motor is started in a first control mode, and when a value corresponding to a rotation speed of a rotor of the first motor exceeds a predetermined value while the first control mode is being executed, the control mode for the first motor is switched from the first control mode to the second control mode, and when the drive of the first motor is to be stopped thereafter, the control mode is switched from the second control mode to the first control mode and then the drive of the first motor is stopped; The control means drives the second motor in the first control mode during a period from start to stop of the second motor. Effect of the Invention

[0013] According to the present invention, it is possible to suppress power consumption in an image forming apparatus and prevent an image from being improperly formed on a recording medium. [Brief description of the drawings]

[0014] [Figure 1] FIG. 2 is a cross-sectional view illustrating an image forming apparatus. [Diagram 2]3 is a diagram illustrating a configuration for bringing a transfer roller into contact with and separating a photosensitive drum corresponding to the transfer roller; FIG. [Diagram 3] FIG. 2 is a block diagram showing a control configuration of the image forming apparatus. [Figure 4] 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. [Diagram 5] FIG. 2 is a block diagram showing a configuration of a motor control device. [Figure 6] FIG. 2 is a block diagram showing a configuration of a command generator. [Figure 7] FIG. 13 is a diagram showing an example of a method for performing a microstep driving method. [Figure 8] FIG. 4 is a diagram illustrating switching of a motor control method. [Figure 9] FIG. 1 is a block diagram showing a configuration of a motor control device that performs speed feedback control. [Figure 10] 1 is a diagram showing the relationship between a command speed ω_ref and an actual rotation speed ω in conventional motor control. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] Preferred embodiments 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 embodiments 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 embodiments.

[0016] [First embodiment] [Image forming device] 1 is a cross-sectional view showing the configuration of a color electrophotographic copying machine (hereinafter referred to as an image forming apparatus) 100 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 has an original reading device 200 including an original feeding device 201 and a reading device 202, and an image printing device 301.

[0018] <Document reader> The documents P loaded on the document stacking section 2 of the document feeder 201 are fed one by one by the pickup roller 3, and then transported further downstream by the feed roller 4. A separation roller 5 that is in pressure contact with the feed roller 4 is provided at a position opposite to the 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 the function of separating documents that are fed in a two-sheet overlapping state.

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

[0020] The document P is conveyed by the feed roller 4 and the like, and is discharged onto the discharge tray 10 by the discharge roller 11 .

[0021] The reading device 202 is provided with a document reading section 16 that reads an image on the 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] Further, the document feeder 201 is provided with a document reading unit 17 that reads an image on the second side of the document being transported. The 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] The document is read as described above.

[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] <Image printing device> A sheet storage tray 18 for storing recording media is provided inside the image printing device 301. Note that the recording media are those on which an image is formed by the image forming device, and include, for example, paper, resin sheets, cloth, OHP sheets, labels, etc.

[0026] The recording medium stored in the sheet storage tray 18 is sent out by a pickup roller 19 and is sent to a registration roller 20 by each transport roller.

[0027] The leading edge of the recording medium conveyed by the pre-registration roller 37 abuts against the registration roller 20. As a result, a loop is formed between the registration roller 20 and the pre-registration roller 37, and the skew of the recording medium is corrected (reduced).

[0028] The image signal output from the document reading device 200 is input for each color component to optical scanning devices 21Y, 21M, 21C, and 21K including a semiconductor laser and a polygon mirror. Specifically, the image signal for yellow output from the document reading device 200 is input to optical scanning device 3Y, and the image signal for magenta output from the document reading device 200 is input to optical scanning device 3M. In addition, the image signal for cyan output from the document reading device 200 is input to optical scanning device 3C, and the image signal for black output from the document reading device 200 is input to optical scanning device 3K. In the following description, a configuration for forming a yellow image will be described, but the same configuration applies to magenta, cyan, and black.

[0029] The outer peripheral surface of the photosensitive drum 22Y as a photoconductor is charged by the charger 23Y. After the outer peripheral surface of the photosensitive drum 22Y is charged, a laser beam corresponding to an image signal input from the document reading device 200 to the optical scanning device 21Y is irradiated onto the outer peripheral surface of the photosensitive drum 22Y from the optical scanning device 21Y via an optical system including a polygon mirror and a mirror. As a result, an electrostatic latent image is formed on the outer peripheral surface of the photosensitive drum 22Y.

[0030] Next, the electrostatic latent image is developed by toner in a developing device 24Y as a developing unit, and a toner image is formed on the outer peripheral surface of the photosensitive drum 22Y. The toner image formed on the photosensitive drum 22Y is transferred to a transfer belt 27 as an intermediate transfer body by a transfer roller 25Y provided at a position facing the photosensitive drum 22Y. Note that the toner remaining on the outer peripheral surface of the photosensitive drum 22Y after the toner image is transferred to the transfer belt 27 is collected by a cleaning unit 26Y.

[0031] The yellow, magenta, cyan, and black toner images transferred to the transfer belt 27 as a transfer unit are transferred to the recording medium by the transfer roller pair 28. A high voltage is applied to the transfer roller pair 28, and the toner images are transferred to the recording medium due to the high voltage. In accordance with this transfer timing, the registration roller 20 sends the recording medium to the transfer roller pair 28. When the registration roller 20 sends the recording medium whose skew has been corrected to the transfer roller pair 28, the pre-registration roller 37 and the roller that forms a nip portion together with the pre-registration roller 37 may be separated. By separating the pre-registration roller 37 and the roller that forms a nip portion together with the pre-registration roller 37, it is possible to prevent wrinkles from occurring in the recording medium being conveyed by the registration roller 20.

[0032] As described above, the recording medium onto which the toner image has been transferred is sent to the fixing device 29 as a fixing section, and the toner image is fixed to the recording medium by heating and pressurizing the recording medium by the fixing device 29. In this manner, an image is formed on the recording medium by the image forming apparatus 100.

[0033] When a monochrome image is formed on a recording medium, the transfer rollers 25Y, 25M, and 25C are separated from the photosensitive drums 22Y, 22M, and 22C, respectively. FIG. 2 is a diagram for explaining a configuration for bringing the transfer rollers and the photosensitive drums corresponding to the transfer rollers into contact with each other and separating them from each other. As shown in FIG. 2(a), the rotation shaft 32a of the tension roller 32 that tensions the transfer belt 27 is held by a holding portion 35. The holding portion 35 is rotatable about the rotation shaft 35a as a rotation shaft, and is supported by a stopper 37 so as not to rotate counterclockwise in FIG. 2(a). The rotation shaft 25Ya of the transfer roller 25Y is held by a holding portion 36Y. The holding portion 36Y is rotatable about the rotation shaft 36Ya as a rotation shaft, and is supported by a stopper 38Y so as not to rotate counterclockwise in FIG. 2(a). The rotation shaft 25Ma of the transfer roller 25M is held by a holding portion 36M. The holding portion 36M is rotatable about a rotation axis 36Ma, and is supported by a stopper 38M so as not to rotate counterclockwise in FIG. 2(a). The rotation axis 25Ca of the transfer roller 25C is held by the holding portion 36C. The holding portion 36C is rotatable about a rotation axis 36Ca, and is supported by a stopper 38C so as not to rotate counterclockwise in FIG. 2(a).

[0034] The stoppers 37, 38Y, 38M, and 38C are provided on the arm portion 33. When the cam 34 rotates clockwise in FIG. 2(a), the arm portion 33 moves rightward. The cam 34 is driven by a stepping motor 403 (described later) and rotates around a rotation shaft 34a as a rotation shaft. When the cam 34 rotates a predetermined amount and the arm portion 33 moves to the right in FIG. 2(a), each holding portion rotates and the rotation shaft of each roller moves downward in the figure, as shown in FIG. 2(b). As a result, the photosensitive drum and the transfer roller are separated from each other.

[0035] When the cam 34 rotates counterclockwise by a predetermined amount in the state shown in Fig. 2(b), the arm portion 33 moves to the left and returns to the state shown in Fig. 2(a). That is, the cam 34 and the arm portion 33 as the moving member move between the first position shown in Fig. 2(a) and the second position shown in Fig. 2(b).

[0036] In this manner, in this embodiment, a monochrome image is formed on the recording medium in a state where the transfer rollers 25Y, 25M, and 25C (and the transfer belt 27) are separated from the photosensitive drums 22Y, 22M, and 22C. As a result, deterioration of the surfaces of the photosensitive drums 22Y, 22M, and 22C can be suppressed.

[0037] When an image is formed in a single-sided printing mode, the recording medium that has passed through the fixing device 29 is discharged to a discharge tray 31 by a paper discharge roller 30. When an image is formed in a double-sided printing mode, the fixing device 29 performs a fixing process on the first side of the recording medium, and then the recording medium is conveyed to a reversing path 32 by a reversing roller 38. The recording medium conveyed to the reversing path 32 is reversed between the first side and the second side by the reversing roller 38 and conveyed to a conveying guide provided with conveying rollers 33, 34, 35, and 36. The recording medium is conveyed again to the registration roller 20 by the conveying rollers 33, 34, 35, and 36, and an image is formed on the second side of the recording medium by the method described above. Thereafter, the recording medium is discharged to a paper discharge tray 31 by a paper discharge roller 30.

[0038] The configuration and functions of image forming apparatus 100 have been described above.

[0039] <Control configuration of image forming apparatus> Fig. 3 is a block diagram showing an example of a control configuration of the image forming apparatus 100. As shown in Fig. 3, 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, motor control devices 157 and 158, sensors 159, and an AC driver 160. The system controller 151 is capable of transmitting and receiving data and commands to and from each of the connected units.

[0040] 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.

[0041] 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 devices 157 and 158, and information received from operation unit 152.

[0042] 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.

[0043] High voltage control unit 155 supplies necessary voltage to high voltage unit 156 (chargers 23Y, 23M, 23C, and 23K, developers 24Y, 24M, 24C, and 24K, transfer roller pair 28, etc.) in accordance with a set value set by system controller 151.

[0044] The motor control device 157 as a control means controls a stepping motor 402 as a drive motor that drives a conveying roller that conveys a recording medium in response to a command output from the CPU 151a. The motor control device 157 also controls a stepping motor 403 that drives a cam mechanism (described later) in response to a command output from the CPU 151a. That is, the motor control device 157 in this embodiment can control a plurality of motors. Although only one motor control device is shown in FIG. 3, two or more motor control devices are actually provided in the image forming apparatus. Although only two motors are shown in FIG. 3, three or more motors are actually provided in the image forming apparatus.

[0045] 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 29.

[0046] 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.

[0047] As described above, the system controller 151 controls the operation sequence of the image forming apparatus 100 .

[0048] [Motor control device] Next, the motor control device 157 will be described. The motor control device 157 in this embodiment can control the motor to be controlled by either of the control methods of constant current control as a first control mode and vector control as a second control mode. Note that in the following description, the following control is performed based on the rotation phase θ, command phase θ_ref, and 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.

[0049] {Vector control} First, a method in which the motor control device 157 in this embodiment controls the stepping motor 402 by vector control will be described with reference to Figures 4 and 5. Note that the stepping motor 402 described below is not provided with a sensor such as a rotary encoder for detecting the rotational phase of the rotor of the motor, but may be configured with a sensor such as a rotary encoder.

[0050] FIG. 4 is a diagram showing the relationship between a stepping motor 402 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. 4, 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. 4, 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 (a 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.

[0051] 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.

[0052] 5 is a block diagram showing an example of the configuration of the motor control device 157 that controls the stepping motor 402. The motor control device 157 is configured with at least one ASIC, and executes each function described below.

[0053] 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.

[0054] The motor control device 157 determines the rotational phase θ of the rotor of the stepping motor 402 by a method described later, and performs vector control based on the result of the determination.

[0055] When the CPU 151a outputs an instruction to start driving the stepping motor 402 to the motor control device 157, the pulse generator 501 outputs a drive pulse to the command generator 500 as a command to drive the motor based on the operation sequence of the stepping motor 402. Note that the operation sequence of the motor (motor drive pattern) is stored in, for example, a memory provided inside the pulse generator 501, and the pulse generator 501 outputs a drive pulse as a pulse train based on the operation sequence.

[0056] The command generator 500 generates and outputs a command phase θ_ref that indicates a target phase of the rotor 402, based on a drive pulse output from a pulse generator 501. The configuration of the command generator 500 will be described later.

[0057] 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.

[0058] 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 output 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 output from the subtractor 101 becomes zero. Note that 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. Also, 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. Also, the D 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 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. When a permanent magnet is used for the rotor, the d-axis current command value id_ref, which affects the strength of the magnetic flux penetrating the winding, is usually set to 0, but is not limited to this.

[0059] The drive current flowing through the A-phase winding of the stepping motor 402 is detected by a current detector 507, and then converted from an analog value to a digital value by an A / D converter 510. The drive current flowing through the B-phase winding of the stepping motor 402 is detected by a current detector 508, and then converted from an analog value to a digital value by an A / D converter 510. The period (predetermined period) at which the current detectors 507 and 508 detect the current is, for example, a period (e.g., 25 μs) that is equal to or shorter than the period T at which the phase controller 502 acquires the deviation Δθ.

[0060] 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 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. 4. 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*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 .

[0061] 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. id = cosθ*iα + sinθ*iβ (3) iq = -sinθ*iα+cosθ*iβ (4) The subtractor 102 receives the q-axis current command value iq_ref output from the phase controller 502 and the current value iq output from the coordinate converter 511. 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.

[0062] Further, the subtractor 103 receives the d-axis current command value id_ref output from the phase controller 502 and the current value id output from the coordinate converter 511. 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.

[0063] The current controller 503 generates a driving voltage Vq based on PID control so as to reduce the deviation output from the subtractor 102. Specifically, the current controller 503 generates a driving voltage Vq so as to make the deviation output from the subtractor 102 zero, and outputs the generated driving voltage Vq to the coordinate inverse converter 505.

[0064] Moreover, the current controller 503 generates a driving voltage Vd based on the PID control so as to reduce the deviation output from the subtractor 103. Specifically, the current controller 503 generates a driving voltage Vd so as to make the deviation output from the subtractor 103 zero, and outputs the driving voltage Vd to the coordinate inverse converter 505.

[0065] In addition, 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.

[0066] 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. 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 .

[0067] 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 stepping motor 402 by supplying the drive currents iα and iβ to the windings of each phase of the stepping motor 402. That is, the PWM inverter 506 functions as a supply means for supplying current to the windings of each phase of the stepping motor 402. 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.

[0068] 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 stepping motor 402 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. 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 stepping motor 402 being used, and are stored in advance in the ROM 151b or a memory (not shown) provided in the motor control device 157.

[0069] The induced voltages Eα and Eβ determined by the induced voltage determiner 512 are output to a phase determiner 513 .

[0070] 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. θ=tan^-1(-Eβ / Eα) (9)

[0071] 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 memory 513a, which indicates the relationship between the induced voltages Eα and Eβ and the rotation phase θ corresponding to the induced voltages Eα and Eβ.

[0072] 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 .

[0073] When vector control is performed, the motor control device 157 repeats the above-mentioned control.

[0074] 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.

[0075] {Constant current control} Next, a method of controlling the stepping motor 402 by constant current control will be described.

[0076] 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.

[0077] In the following description, the motor is controlled by supplying a current of a predetermined magnitude to the windings of the motor during constant current control, but this is not limiting. For example, the motor may be controlled by supplying a current of a predetermined magnitude to the windings of the motor during acceleration and deceleration, respectively, during constant current control.

[0078] 5, a command generator 500 outputs a command phase θ_ref to a constant current controller 517 based on a drive pulse output from a pulse generator 501. 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 the current vector corresponding to the current command values ​​iα_ref and iβ_ref in the stationary coordinate system is always constant.

[0079] The drive currents flowing through the A-phase and B-phase windings of the stepping motor 402 are detected by current detectors 507 and 508. The detected drive currents are converted from analog values ​​to digital values ​​by the A / D converter 510, as described above.

[0080] 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.

[0081] 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.

[0082] 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.

[0083] 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 .

[0084] 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.

[0085] {command generator} Fig. 6 is a block diagram showing the configuration of a command generator 500 in this embodiment. As shown in Fig. 6, the command generator 500 has a speed generator 500a that generates a rotation speed ω_ref' indicating a target speed of a rotor of the stepping motor 402, and a command value generator 500b that generates a command phase θ_ref based on a drive pulse output from a pulse result 501.

[0086] The velocity generator 500a generates and outputs a rotation velocity ω_ref' based on the time interval between the falling edges of successive drive pulses. That is, the rotation velocity ω_ref' changes with a period corresponding to the period of the drive pulse.

[0087] 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. θ_ref=θini+θstep*n (10)

[0088] 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.

[0089] {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.

[0090] Fig. 7 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.

[0091] A method of performing microstep driving in this embodiment will be described below with reference to Figures 6 and 7. The driving pulse and command phase shown in Figure 7 indicate a state in which the rotor rotates at a constant speed.

[0092] The lead of the command phase θ_ref in the microstep driving method is 90°, which is the lead of the command phase θ_ref in the full-step driving 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 7, allowing for more precise control of the rotor rotation phase θ.

[0093] 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. θ_ref=45°+90 / N°*n (11)

[0094] 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 pulse generator 501 corresponds to the command phase. The period (frequency) of the drive pulse output from the CPU 151a corresponds to the target speed (command speed) of the stepping motor 402.

[0095] {Switching between vector control and constant current control} Next, a method of switching from constant current control to vector control will be described. As shown in FIG. 5, the motor control device 157 in this embodiment has a configuration for switching between constant current control and vector control when controlling the stepping motor 402. Specifically, the motor control device 157 has a control switch 515 and changeover switches 516a and 516b. During the period in which the constant current control is being performed, the circuit that performs the vector control may be operating or may be stopped. During the period in which the vector control is being performed, the circuit that performs the constant current control may be operating or may be stopped.

[0096] 6, the rotation speed ω_ref' output from the speed generator 500a is input to the control switch 515. The control switch 515 compares the rotation speed ω_ref' with a threshold value ωth as a predetermined value, and switches the motor control method from constant current control to vector control based on the comparison result.

[0097] 8 is a diagram for explaining the switching of the control method. Note that, although the threshold value ωth in this embodiment is set to the smallest rotation speed among the rotation speeds at which the rotation phase θ is determined with high accuracy, this is not limiting. For example, the threshold value ωth may be set to a value equal to or greater than the smallest rotation speed among the rotation speeds at which the rotation phase θ is determined with high accuracy. Also, the threshold value ωth is stored in advance in, for example, the memory 515a provided in the control switcher 515.

[0098] The control switch 515 sets the switching signal to 'H' when constant current control is performed, and sets the switching signal to 'L' when vector control is performed. The switching signal output from the control switch 515 is input to each switch as shown in Fig. 5. Note that the control switch 515 outputs the switching signal, for example, at the same cycle as the cycle at which the rotation speed ω_ref' is input.

[0099] During constant current control, if the rotation speed ω_ref' is smaller than the threshold value ωth (ω_ref'<ωth), the control switch 515 does not switch the control mode for controlling the stepping motor 402. That is, the control switch 515 outputs a switching signal 'H' so as to maintain the state in which the stepping motor 402 is controlled by the constant current control. As a result, the states of the switches 516a, 516b, and 516c are maintained, and the constant current control continues.

[0100] Furthermore, during constant current control, when the rotation speed ω_ref' becomes equal to or greater than the threshold value ωth (ω_ref'≧ωth), the control switch 515 switches the control mode for controlling the stepping motor 402. That is, the control switch 515 outputs a switching signal that is switched from 'H' to 'L' so that the stepping motor 402 is controlled by vector control. As a result, the states of the switches 516a, 516b, and 516c are switched in response to the switching signal, and vector control is performed.

[0101] During vector control, if the rotation speed ω_ref' is equal to or greater than the threshold value ωth (ω_ref'≧ωth), the control switch 515 does not switch the control mode for controlling the stepping motor 402. That is, the control switch 515 outputs a switching signal 'L' so as to maintain the state in which the stepping motor 402 is controlled by vector control. As a result, the states of the switches 516a, 516b, and 516c are maintained, and the vector control continues.

[0102] Furthermore, during vector control, when the rotation speed ω_ref' is smaller than the threshold value ωth (ω_ref'<ωth), the control switch 515 switches the control mode for controlling the stepping motor 402. That is, the control switch 515 outputs a switching signal switched from 'L' to 'H' so that the stepping motor 402 is controlled by constant current control. As a result, the states of the switches 516a, 516b, and 516c are switched in response to the switching signal, and constant current control is performed.

[0103] Next, a description will be given of a method in which the motor control device 157 controls the stepping motor 403. In this embodiment, the stepping motor 403 is controlled by constant current control as the first control mode.

[0104] When the CPU 151a outputs an instruction to start driving the stepping motor 403 to the motor control device 157, the pulse generator 810 outputs a drive pulse to the command generator 811 as a command to drive the motor based on the operation sequence of the stepping motor 403. Note that the operation sequence of the motor (motor drive pattern) is stored, for example, in a memory provided inside the pulse generator 810, and the pulse generator 810 outputs a drive pulse as a pulse train based on the operation sequence.

[0105] Similar to the command generator 501 , the command generator 811 generates and outputs a command phase θ_ref representing a target phase of the rotor 402 based on the drive pulse output from the pulse generator 810 .

[0106] The constant current controller 801 generates and outputs current command values ​​iα_ref and iβ_ref in the stationary coordinate system, which correspond to the command phase θ_ref output from the command generator 811 .

[0107] The drive currents flowing through the A-phase and B-phase windings of the stepping motor 403 are detected by current detectors 806 and 807. The detected drive currents are converted from analog values ​​to digital values ​​by an A / D converter 809 and expressed as current values ​​iα and iβ as shown in equations (1) and (2).

[0108] The subtractor 802 receives the current value iα output from the A / D converter 809 and the current command value iα_ref output from the constant current controller 801. The subtractor 802 calculates the deviation between the current command value iα_ref and the current value iα, and outputs the deviation to the current controller 804.

[0109] Further, the subtractor 803 receives the current value iβ output from the A / D converter 809 and the current command value iβ_ref output from the constant current controller 801. The subtractor 803 calculates the deviation between the current command value iβ_ref and the current value iβ, and outputs the deviation to the current controller 804.

[0110] The current controller 804 outputs the drive voltages Vα and Vβ based on the PID control so that the input deviation becomes small. Specifically, the current controller 804 outputs the drive voltages Vα and Vβ so that the input deviation approaches 0.

[0111] The PWM inverter 805 supplies drive currents to the windings of each phase of the stepping motor 403 based on the input drive voltages Vα and Vβ in the manner described above, thereby driving the stepping motor 403 .

[0112] [Application examples of vector control and constant current control] Next, an application example of vector control and constant current control in this embodiment will be described.

[0113] In this embodiment, the stepping motor 402 drives a conveying roller (for example, a conveying roller such as the registration roller 20) provided in the image printing device 301. That is, in this embodiment, the motor (for example, the stepping motor 402) that drives the conveying roller that conveys the recording medium starts to be driven by constant current control, and then the control mode is switched from constant current control to vector control. That is, in this embodiment, the recording medium is conveyed by the conveying roller driven by the motor controlled by vector control. As a result, the power consumption in the image forming apparatus is suppressed (reduced) compared to the case where the recording medium is conveyed by the conveying roller driven by the motor controlled by constant current control without using vector control. In addition, it is possible to reduce noise generated due to the motor being controlled by constant current control. Note that the stepping motor 402 is stopped after the control mode is switched from vector control to constant current control. In this embodiment, a stepping motor is used as the motor that drives the conveying roller, but a brushless DC motor or the like may be used.

[0114] On the other hand, in the contact / separation configuration as shown in FIG. 2, it is necessary to control the amount of rotation of the cam 34 with high precision. Specifically, it is necessary to control the stop position of the cam 34 with high precision. In other words, it is necessary to control the phase at which the rotor of the stepping motor 403 stops with high precision. Therefore, in this embodiment, the stepping motor 403 is controlled by constant current control during the period from start to stop. As a result, the amount of rotation of the cam 34 is controlled with high precision. As a result, an image is appropriately formed on the recording medium.

[0115] With the above configuration, it is possible to suppress power consumption in the image forming apparatus while suppressing the occurrence of an image not being properly formed on a recording medium.

[0116] In this embodiment, the stepping motor 403 drives a cam for bringing the transfer rollers 25Y, 25M, and 25C into contact with and away from the photosensitive drums 22Y, 22M, and 22C, but this is not limiting. For example, the stepping motor 403 may be configured to drive a cam for bringing a pair of rollers provided in the fixing device 29 into contact with and away from each other. This configuration can prevent an image from being improperly formed on a recording medium.

[0117] Also, for example, the stepping motor 403 may be configured to drive a cam for bringing the pre-registration roller 37 into contact with and away from a roller that forms a nip portion together with the pre-registration roller 37. With this configuration, the distance between the rotation axis of the pre-registration roller 37 and the rotation axis of the roller that forms a nip portion together with the pre-registration roller 37 can be adjusted with high precision. In other words, the nip pressure of the transport roller that transports the recording medium can be appropriately adjusted. As a result, the recording medium can be appropriately transported without damaging the recording medium, and an image is appropriately formed on the recording medium.

[0118] As described above, the stepping motor 403 may be configured to drive an adjustment member that adjusts the distance between the rotation axis of the first rotating body and the rotation axis of the second rotating body that forms a nip portion together with the first rotating body. With this configuration, the distance between the rotation axis of the first rotating body and the rotation axis of the second rotating body can be adjusted with high precision. As a result, an image is appropriately formed on the recording medium.

[0119] For example, a configuration may be adopted in which a motor that drives a first rotating body is driven by vector control, and a motor that drives an adjustment member that adjusts the distance between the rotation axis of the first rotating body and the rotation axis of a second rotating body that forms a nip portion together with the first rotating body is driven by constant current control.

[0120] In this embodiment, the stepping motor 402 and the stepping motor 403 are controlled by the motor control device 157, which is one control IC, but this is not limited to the above. For example, the control IC that controls the stepping motor 402 and the control IC that controls the stepping motor 403 may be separate ICs. In this case, the control IC that controls the stepping motor 402 and the control IC that controls the stepping motor 403 are included in the control means.

[0121] In the vector control of this embodiment, the stepping motor 402 is controlled by performing phase feedback control, but the present invention is not limited to this. For example, the stepping motor 402 may be controlled by feeding back the rotation speed ω of the rotor of the stepping motor 402. Specifically, as shown in FIG. 9, a command generator 500 outputs a command speed ω_ref representing a target speed of the rotor. Furthermore, a speed determiner 514 provided inside the motor control device 157 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. ω=dθ / dt (12)

[0122] 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. Such a configuration for performing speed feedback control may be used. In such a configuration, since the rotation speed is fed back, it is possible to control the rotation speed of the rotor to a predetermined speed. Note that the method for determining the rotation speed ω is one example, and any known method may be used.

[0123] In addition, in this embodiment, switching between constant current control and vector control is performed by comparing the rotation speed ω_ref' as a value corresponding to the rotation speed of the rotor of the stepping motor 402 with the threshold value ωth, but this is not limited to the above. For example, switching between constant current control and vector control may be performed by comparing the rotation speed ω determined by the speed determiner 514 as shown in Fig. 9 as a value corresponding to the rotation speed of the rotor of the stepping motor 402 with the threshold value ωth. [Explanation of symbols]

[0124] 22Y, 22M, 22C, 22K Photosensitive drum 27 Transfer belt 28 Transfer roller 33 Arm section 34 Cam 37 Pre-registration roller 157 Motor control device 402, 403 Stepping motor 517 Constant Current Controller 518 Vector Controller

Claims

1. A first rotating body; A second rotor that rotates while forming a nip portion with the first rotor; a moving means for moving the first rotating body so as to adjust a distance between the first rotating body and the second rotating body; A conveying roller for conveying a sheet; A first motor that drives the conveying roller; A second motor for driving the moving means; a phase determining means for determining a rotational phase of a rotor of the first motor; a control means for executing control including a first control mode for controlling the motor based on a current of a predetermined magnitude and a second control mode for controlling the motor based on the rotation phase determined by the phase determination means; Equipped with the control means starts driving the first motor in the first control mode, and when a value corresponding to the rotation speed of the rotor of the first motor exceeds a predetermined value while the first control mode is being executed, switches the control mode of the first motor from the first control mode to the second control mode, and when stopping the driving of the first motor thereafter, switches from the second control mode to the first control mode and then stops the driving of the first motor; The sheet conveying device, wherein the control means drives the second motor in the first control mode during a period from start to stop of the second motor.

2. the control means, in the second control mode, executes vector control so as to reduce a difference between the rotational phase determined by the phase determination means and an instruction phase representing a target phase of the rotor of the first motor, The sheet conveying device according to claim 1, characterized in that the vector control is a control method for driving the first motor based on a torque current component that generates torque in a rotor of the first motor, the torque current component being expressed in a rotating coordinate system based on the rotational phase determined by the phase determination means.

3. a speed determining means for determining a rotational speed of a rotor of the first motor; the control means, in the second control mode, executes vector control so as to reduce a difference between the rotation speed determined by the speed determination means and an instruction speed representing a target speed of the rotor of the first motor, The sheet conveying device according to claim 1, characterized in that the vector control is a control method for driving the first motor based on a torque current component which is expressed in a rotating coordinate system based on the rotational phase determined by the phase determination means and is a current component that generates torque in a rotor of the first motor.

4. The first motor further includes a current detection means for detecting a drive current flowing through a winding of the first motor, 4. The sheet transport device according to claim 1, wherein the phase determining means determines a rotational phase of the rotor of the first motor based on the drive current detected by the current detecting means.

5. the control means includes a voltage determination means for determining an induced voltage generated in a winding of the first motor by rotation of a rotor of the first motor based on a drive current detected by the current detection means, 5. The sheet transport device according to claim 4, wherein the phase determining means determines the rotation phase of the rotor of the first motor based on the induced voltage determined by the voltage determining means.

6. 2. The sheet transport device according to claim 1, wherein the value corresponding to the rotation speed of the rotor of the first motor is a value representing a target speed of the rotor of the first motor.

7. 7. The image forming apparatus according to claim 1, wherein the control unit includes a control IC capable of controlling the first motor and the second motor.

8. 8. The sheet transport device according to claim 1, wherein the moving means is a cam.

9. 9. The sheet conveying device according to claim 1, wherein the first motor is a stepping motor.

10. 9. The sheet conveying device according to claim 1, wherein the first motor is a DC brushless motor.

11. The sheet nipped in the nip portion is conveyed by the first rotating body and the second rotating body, 11. The sheet conveying device according to claim 1, wherein the moving means moves the first rotating body so as to adjust a distance between a rotation axis of the first rotating body and a rotation axis of the second rotating body.

12. The sheet transport device of claim 11, further comprising an abutment member that is positioned downstream of the first rotating body in the sheet transport direction, against which the sheet transported by the first rotating body and the second rotating body abuts, and which is used to correct the skew of the sheet by bending the sheet between the first rotating body and the second rotating body in the sheet transport direction.

13. 13. The sheet transport device according to claim 12, wherein the contact member is a pair of rollers that further transport the sheet transported by the first rotating body and the second rotating body.

14. A sheet conveying device according to any one of claims 1 to 10, an image forming unit for forming a toner image on the sheet conveyed by the sheet conveying device, the second rotating body is a photoreceptor on which a toner image is formed by the image forming unit, The first rotating body is a transfer roller that moves to switch an intermediate transfer body, onto which a toner image formed on the photosensitive body is transferred, between a contact state and a spaced state with respect to the photosensitive body, and is characterized in that the first rotating body forms the nip portion with the second rotating body via the intermediate transfer body.

15. A sheet conveying device according to any one of claims 1 to 10, an image forming unit for forming a toner image on the sheet conveyed by the sheet conveying device, The image forming apparatus is characterized in that the first rotating body and the second rotating body constitute a fixing unit that fixes a toner image formed on a sheet.

Images