Image forming apparatus

Abstract

To solve the problem in which: when an image is formed on thick paper, the accuracy of calculating torque may be reduced due to a relatively small inductive voltage induced by winding of a motor.SOLUTION: When image formation is performed on thick paper, torque T is determined based on a torque constant Kt that is determined when an image forming apparatus 100 is powered on. When image formation is performed on normal paper, torque T is determined based on the torque constant Kt that is determined when the image forming apparatus 100 is powered on. Every time a current value iq, inductive voltages Eα, Eβ, and a rotational phase θ are input, the torque constant Kt is determined. As a result of this, load torque applied to a motor can be accurately determined.SELECTED DRAWING: Figure 5

Description

Technical Field

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

Background Art

[0002] Conventionally, a configuration for calculating a torque constant for calculating the torque applied to the rotor of a motor based on the induced voltage induced in the winding of the motor and the rotational speed of the rotor of the motor as the rotor rotates is known (Patent Document 1). In Patent Document 1, an abnormality in a load that is a driving target of the motor is detected based on the calculated torque.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] The induced voltage induced in the winding of the motor as the rotor of the motor rotates becomes smaller as the rotational speed of the rotor of the motor becomes smaller. That is, the accuracy of calculating the torque constant decreases as the rotational speed of the rotor of the motor decreases, and as a result, the accuracy of calculating the torque also decreases.

[0005] In an image forming apparatus, for example, the speed at which thick paper is conveyed when an image is formed on the thick paper is smaller (for example, 1 / 2 times) than the speed at which plain paper is conveyed when an image is formed on the plain paper. Therefore, when an image is formed on thick paper, the accuracy of calculating the torque may decrease due to the relatively small induced voltage induced in the winding of the motor. As a result, the accuracy of detecting an abnormality in the load that is the driving target of the motor also decreases. Further, for example, in a configuration for predicting the life of a load that is a driving target of the motor based on torque, the accuracy of predicting the life decreases.

[0006] In view of the above problems, the present invention aims to determine the load torque applied to a motor with greater accuracy. [Means for solving the problem]

[0007] To solve the above problems, the image forming apparatus according to the present invention is: In an image forming apparatus equipped with image forming means for forming an image on a recording medium, A transport unit for transporting the recording medium, A motor that drives the transport unit, A detection means for detecting the drive current flowing through the windings of the motor, A phase determination means that determines the rotational phase of the motor rotor based on the drive current detected by the detection means, A control means for performing vector control to control the rotation of the motor based on a torque current component, which is a current component that generates torque in the rotor and is represented in a rotating coordinate system based on the rotational phase determined by the phase determination means, and an excitation current component, which is a current component that affects the intensity of the magnetic flux passing through the winding and is represented in the rotating coordinate system; A voltage determination means that determines the magnitude of the induced voltage induced in the winding by the rotation of the rotor, based on the drive current detected by the detection means, A first determination means for determining a torque constant based on the rotational phase determined by the phase determination means and the magnitude of the induced voltage determined by the voltage determination means, Based on the value of the torque current component of the drive current detected by the detection means and the torque constant determined by the first determination means, The aforementioned A second determination means for determining the load torque applied to the rotor, It has, The control means rotates the motor at a first speed when an image is formed on a first recording medium having a first basis weight, and rotates the motor at a second speed slower than the first speed when an image is formed on a second recording medium having a second basis weight greater than the first basis weight. When the power supply of the image forming apparatus is turned on from an off state, the control means performs an initial operation to rotate the motor at a third speed greater than the second speed. The first determination means determines the torque constant based on the rotational phase determined by the phase determination means and the magnitude of the induced voltage determined by the voltage determination means during the initial operation. The second determination means determines the load torque based on the torque constant determined based on the rotation phase and the magnitude of the induced voltage, which were determined when the motor was rotating at the third speed during the initial operation, if an image is formed on the second recording medium. The second determination means is characterized in that, when an image is formed on the first recording medium, it determines the load torque based on the torque constant determined based on the rotational phase determined by the phase determination means and the magnitude of the induced voltage determined by the voltage determination means while the motor is rotating at the first speed for transporting the first recording medium. [Effects of the Invention]

[0008] According to the present invention, the load torque applied to the motor can be determined with greater precision. [Brief explanation of the drawing]

[0009] [Figure 1] This is a cross-sectional view illustrating an image forming apparatus according to the first embodiment. [Figure 2] This is a block diagram showing the control configuration of the image forming apparatus. [Figure 3] This figure shows the relationship between a two-phase motor consisting of phases A and B, and the d-axis and q-axis of a rotating coordinate system. [Figure 4]It is a block diagram showing the configuration of a motor control device. [Figure 5] It is a block diagram showing the configuration of a torque detector. [Figure 6] It is a timing chart showing the timing for determining (acquiring) the torque constant Kt when cardboard is conveyed. [Figure 7] It is a timing chart showing the timing for determining (acquiring) the torque constant Kt when plain paper is conveyed. [Figure 8] It is a diagram showing the relationship between the number of image formation sheets (printing sheets) and the torque of the motor 509. [Figure 9] It is a block diagram showing the configuration of a motor control device that performs speed feedback control. [Embodiments for Carrying Out the Invention]

[0010] Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. However, the shapes of the component parts described in this embodiment and their relative arrangements, etc. should be appropriately changed according to the configuration of the device to which this invention is applied and various conditions, and the scope of this invention is not intended to be limited to the following embodiments. In the following description, the case where a motor control device is provided in an image forming apparatus will be described, but the motor control device is not limited to being provided in an image forming apparatus. For example, the motor control device is also used in a sheet conveying device that conveys sheets such as recording media and originals.

[0011] [First Embodiment] [Image Forming Apparatus] FIG. 1 is a cross-sectional view showing the configuration of a monochrome electrophotographic copying machine (hereinafter referred to as an image forming apparatus) 100 having a sheet conveying device used in this embodiment. Note that the image forming apparatus is not limited to a copying machine, and for example, a facsimile apparatus, a printing machine, a printer, etc. may be used. Further, the recording method is not limited to the electrophotographic method, and for example, an inkjet method, etc. may be used. Furthermore, the form of the image forming apparatus may be either monochrome or color.

[0012] 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 a document reading apparatus 200 including a document feeder 201 and a reading apparatus 202, and an image printing apparatus 301. The document feeder 201 is rotatable with respect to the reading apparatus 202.

[0013] <Document Reading Apparatus> The document P placed on the document stacking unit 2 of the document feeder 201 is fed one by one by the pickup roller 3, and then further conveyed downstream by the feed roller 4. A separation roller 5 that presses against the feed roller 4 is provided at a position facing the feed roller 4. The separation roller 5 is configured to rotate when a load torque of a predetermined torque or more is applied to the separation roller 5, and has a function of separating documents fed in a double-stacked state.

[0014] 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 axis of the paper feed roller 4 so as to be rotatable about the rotation axis of the feed roller 4.

[0015] The document P is conveyed by various conveying rollers such as the feed roller 4 and the conveying roller 6, and is discharged to the discharge tray 10 by the discharge roller 11.

[0016] The document reading apparatus 202 is provided with a document reading unit 16 that reads the image on the first side of the conveyed document. The image information read by the document reading unit 16 is output to the image printing apparatus 301.

[0017] In addition, the document feeder 201 is provided with a document reading unit 17 that reads the image on the second side of the conveyed document. The image information read by the document reading unit 17 is output to the image printing apparatus 301 in the same manner as described for the document reading unit 16.

[0018] As described above, the document is read.

[0019] There are two document scanning modes: a first scanning mode and a second scanning mode. The first scanning mode reads the image of a document that is transported using the method described above. The second scanning mode reads the image of a document placed on the document glass 214 (transparent material) using a document scanning unit 16 that moves at a constant speed. The document is placed on the document glass 214 when the document feeder 201 is rotated relative to the scanning unit 202. Typically, images of sheet-like documents are scanned in the first scanning mode, while images of bound documents such as books and booklets are scanned in the second scanning mode.

[0020] <Image Printing Device> Inside the image printing device 301 are sheet storage trays 302 and 304. Each of the sheet storage trays 302 and 304 can store different types of recording media. For example, sheet storage tray 302 stores A4-sized plain paper, and sheet storage tray 304 stores A4-sized cardboard. A recording medium is any material on which an image is formed by the image forming device; for example, paper, resin sheets, cloth, OHP sheets, labels, etc., are included in recording media.

[0021] The recording media stored in the sheet storage tray 302 are fed by the pickup roller 303 and sent to the registration roller 308 by the transport roller 306. Similarly, the recording media stored in the sheet storage tray 304 are fed by the pickup roller 305 and sent to the registration roller 308 by the transport rollers 307 and 306.

[0022] The image signal output from the document reader 200 is input to the optical scanning device 311, which includes a semiconductor laser and a polygon mirror. The outer surface of the photosensitive drum 309 is charged by the charger 310. After the outer surface of the photosensitive drum 309 is charged, laser light corresponding to the image signal input from the document reader 200 to the optical scanning device 311 is irradiated onto the outer surface of the photosensitive drum 309 from the optical scanning device 311, via the polygon mirror and mirrors 312 and 313. As a result, an electrostatic latent image is formed on the outer surface of the photosensitive drum 309.

[0023] Next, the electrostatic latent image is developed by the toner in the developer unit 314, and a toner image is formed on the outer surface of the photosensitive drum 309. The toner image formed on the photosensitive drum 309 is transferred to the recording medium by the transfer charger 315, which is located opposite the photosensitive drum 309 (the transfer position). The registration roller 308 feeds the recording medium to the transfer position in accordance with the transfer timing at which the image is transferred to the recording medium by the transfer charger 315.

[0024] As described above, the recording medium onto which the toner image has been transferred is fed to the fuser 318 by the transport belt 317, where it is heated and pressurized to fix the toner image to the recording medium. In this way, an image is formed on the recording medium by the image forming apparatus 100.

[0025] When image formation is performed in single-sided printing mode, the recording medium that has passed through the fuser 318 is discharged to an output tray (not shown) by the output rollers 319 and 324. When image formation is performed in double-sided printing mode, after the first surface of the recording medium is fixed by the fuser 318, the recording medium is transported to the inversion path 325 by the output roller 319, the transport roller 320, and the inversion roller 321. The recording medium is then transported again to the registration roller 308 by the transport rollers 322 and 323, and an image is formed on the second surface of the recording medium in the manner described above. The recording medium is then discharged to an output tray (not shown) by the output rollers 319 and 324.

[0026] Furthermore, when a recording medium with an image formed on its first surface is discharged face down from the image forming apparatus 100, the recording medium that has passed through the fuser 318 is transported through the discharge roller 319 toward the transport roller 320. Then, just before the rear end of the recording medium passes through the nip portion of the transport roller 320, the rotation of the transport roller 320 is reversed, so that the recording medium is discharged from the image forming apparatus 100 via the discharge roller 324 with its first surface facing downwards.

[0027] The above describes the configuration and function of the image forming apparatus 100. For example, various rollers in the transport section, such as the pickup rollers 3, 303, 305 and the registration roller 308, as well as the photosensitive drum 309, developer 314, and transport belt 317, correspond to the load. The motor control device of this embodiment can be applied to the motors that drive these loads.

[0028] <Control configuration of an image forming apparatus> Figure 2 is a block diagram showing an example of the control configuration of the image forming apparatus 100. As shown in Figure 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, the operation unit 152, the analog-to-digital (A / D) converter 153, the high-voltage control unit 155, the motor control device 157, the sensors 159, and the AC driver 160. The system controller 151 is capable of sending and receiving data and commands to and from each of the connected units.

[0029] The CPU 151a executes various sequences related to a predetermined image formation sequence by reading and executing various programs stored in the ROM 151b.

[0030] RAM151c is a memory device. RAM151c stores various data, such as setting values ​​for the high-voltage control unit 155, command values ​​for the motor control device 157, and information received from the operation unit 152.

[0031] The system controller 151 transmits setting value data of various devices located inside the image forming apparatus 100, which are necessary for image processing in the image processing unit 112, to the image processing unit 112. Furthermore, the system controller 151 receives signals from sensors 159 and sets the setting values ​​of the high-voltage control unit 155 based on the received signals.

[0032] The high-voltage control unit 155 supplies the necessary voltage to the high-voltage unit 156 (charger 310, developer 314, transfer charger 315, etc.) according to the setting value set by the system controller 151.

[0033] The motor control device 157 controls the motor 509 that drives the load provided in the image printing device 301 in accordance with the command output from the CPU 151a. Although Figure 2 shows one motor as the motor that drives the load, in reality, the image forming apparatus is equipped with two or more motors. Furthermore, a configuration in which one motor control device controls multiple motors is also possible.

[0034] The A / D converter 153 receives a detection signal from the thermistor 154, which detects the temperature of the fuser heater 161, converts the detection signal from an analog signal to a digital signal, and transmits it 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 fuser heater 161 so that its temperature reaches the temperature required for the fixing process. The fuser heater 161 is a heater used for the fixing process and is included in the fuser unit 318.

[0035] The system controller 151 controls the operation unit 152 to display an operation screen on the display unit provided on the operation unit 152, which allows the user to set the type of recording medium to be used (hereinafter referred to as paper type). The system controller 151 receives the 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. This information includes, for example, the number of images to be formed, the progress of the image forming operation, and information regarding sheet jams or double feedings in the image printer 301 and the document feeder 201. The operation unit 152 displays the information received from the system controller 151 on its display unit.

[0036] As described above, the system controller 151 controls the operation sequence of the image forming apparatus 100.

[0037] [Motor control device] Next, the motor control device 157 in this embodiment will be described. In this embodiment, the motor control device 157 controls the motor 509 by vector control.

[0038] <Vector control> First, the method by which the motor control device 157 in this embodiment performs vector control will be explained using Figures 3 and 4. Note that the motor in the following description is not equipped with sensors such as a rotary encoder for detecting the rotational phase of the motor rotor.

[0039] Figure 3 shows the relationship between a stepping motor (hereinafter referred to as the motor) 509, which consists of two phases, A phase (first phase) and B phase (second phase), and a rotating coordinate system represented by the d-axis and q-axis. In Figure 3, in the stationary coordinate system, the α-axis, which corresponds to the winding of the A phase, and the β-axis, which corresponds to the winding of the B phase, are defined. Also in Figure 3, the d-axis is defined along the direction of the magnetic flux created by the magnetic poles of the permanent magnets used in the rotor 402, and the q-axis is defined along the 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 rotational phase of the rotor 402 is represented by the angle θ. In vector control, a rotating coordinate system based on the rotational phase θ of the rotor 402 is used. Specifically, in vector control, the current vector corresponding to the drive current flowing through the windings is used, and its current components in the rotating coordinate system are 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 passing through the windings.

[0040] Vector control is a motor control method that uses phase feedback control to control the values ​​of the torque current component and the excitation current component so that the deviation between the command phase, which represents the target phase of the rotor, and the actual rotational phase is minimized. Another method of controlling a motor is to use speed feedback control to control the values ​​of the torque current component and the excitation current component so that the deviation between the command speed, which represents the target speed of the rotor, and the actual rotational speed is minimized.

[0041] Figure 4 is a block diagram showing an example configuration of the motor control device 600 that controls the motor 509. The motor control device 157 consists of at least one ASIC and performs the functions described below.

[0042] The motor control device 157 includes a phase controller 502, a current controller 503, a coordinate inverse converter 505, a coordinate converter 511, etc., as a circuit for performing vector control. The coordinate converter 511 transforms the current vectors corresponding to the drive currents 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 currents flowing through the windings are represented by the current value of the q-axis component (q-axis current) and the current value of the d-axis component (d-axis current), which are current values ​​in the rotating coordinate system. The q-axis current corresponds to the torque current that generates torque in the rotor 402 of the motor 509. The d-axis current corresponds to the excitation current that affects the strength of the magnetic flux passing through the windings of the motor 509. The motor control device 600 can control the q-axis current and the d-axis current independently. As a result, the motor control unit 157 can efficiently generate the torque necessary for the rotor 402 to rotate by controlling the q-axis current in accordance with the load torque applied to the rotor 402. In other words, in vector control, the magnitude of the current vector shown in Figure 4 changes in accordance with the load torque applied to the rotor 402.

[0043] The motor control device 157 determines the rotational phase θ of the rotor 402 of the motor 509 by a method described later, and performs vector control based on the determination result. The CPU 151a generates a command phase θ_ref representing the target phase of the rotor 402 of the motor 509, and outputs the command phase θ_ref to the motor control device 157. In practice, the CPU 151a outputs a pulse signal to the motor control device 600, where the number of pulses corresponds to the command phase and the pulse frequency corresponds to the target speed. The command phase θ_ref is generated, for example, based on the target speed of the motor 509.

[0044] The subtractor 101 calculates the difference between the rotational phase θ of the rotor 402 of the motor 509 and the command phase θ_ref, and outputs the difference to the phase controller 502.

[0045] The phase controller 502 acquires the deviation output from the subtractor 101 at a predetermined time period T (for example, 200 μs). Based on proportional control (P), integral control (I), and differential control (D), the phase controller 502 generates and outputs the q-axis current command value iq_ref and the d-axis current command value id_ref as target values ​​so that the deviation output from the subtractor 101 becomes small. Specifically, the phase controller 502 generates and outputs the q-axis current command value iq_ref and the d-axis current command value id_ref so that the deviation output from the subtractor 101 becomes 0 based on P control, I control, and D control. In other words, the phase controller 502 functions as a first setting means. P control is a control method that controls the value of the object to be controlled based on a value proportional to the deviation between the command value and the estimated value. I control is a control method that controls the value of the object to be controlled based on a value proportional to the time integral of the deviation between the command value and the estimated value. Furthermore, D control is a control method that controls the value of the object to be controlled based on a value proportional to the time change of the deviation between the command value and the 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 also 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 passing through the winding, is set to 0, but is not limited to this.

[0046] The drive currents flowing through the A-phase and B-phase windings of motor 509 are detected by current detectors 507 and 508. The detected drive current values ​​are expressed as current values ​​iα and iβ in the stationary coordinate system, using the phase θe of the current vector shown in Figure 3, by the following equation. The phase θe of the current vector is defined as the angle between the α-axis and the current vector. I represents the magnitude of the current vector. iα = I * cosθe (1) iβ=I*sinθe (2) These current values ​​iα and iβ are input to the coordinate converter 511 and the induced voltage determiner 512.

[0047] The coordinate converter 511 converts the current values ​​iα and iβ in the stationary coordinate system to the current value iq for the q-axis and the current value id for the d-axis in the rotating coordinate system using 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 as inputs. The subtractor 102 calculates the difference between the q-axis current command value iq_ref and the current value iq, and outputs this difference to the current controller 503.

[0048] Furthermore, 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 as inputs. The subtractor 103 calculates the difference between the d-axis current command value id_ref and the current value id, and outputs this difference to the current controller 503.

[0049] The current controller 503 generates drive voltages Vq and Vd based on PID control so that the input deviations are minimized. Specifically, the current controller 503 generates drive voltages Vq and Vd so that the input deviations are zero and outputs them to the coordinate inverse converter 505. In this embodiment, the current controller 503 generates drive voltages Vq and Vd based on PID control, but is not limited to this. For example, the current controller 503 may generate drive voltages Vq and Vd based on PI control.

[0050] The coordinate inverse converter 505 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 using the following equation. 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.

[0051] The PWM inverter 506 has a full-bridge circuit. The full-bridge circuit is driven by a PWM (pulse width modulation) signal based on 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 corresponding to the drive voltages Vα and Vβ, and drives the motor 509 by supplying the drive currents iα and iβ to the windings of each phase of the motor 509. In this embodiment, the PWM inverter has a full-bridge circuit, but the PWM inverter may also be a half-bridge circuit or the like.

[0052] Next, the method for determining the rotational phase θ will be explained. To determine the rotational phase θ of the rotor 402, the values ​​of the 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 are used. The values ​​of the induced voltages are determined (calculated) by the induced voltage determination unit 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 determination unit 512 and the drive voltages Vα and Vβ input from the coordinate inverse converter 505 to the induced voltage determination unit 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 winding inductance L (hereinafter referred to as control values) are specific to the motor 509 being used and are pre-stored in ROM 151b.

[0053] The induced voltages Eα and Eβ determined by the induced voltage determiner 512 are output to the phase determiner 513.

[0054] The phase determiner 513 determines the rotational phase θ of the rotor 402 of the motor 509 based on the ratio of the induced voltage Eα and the induced voltage Eβ output from the induced voltage determiner 512, according to the following equation. θ = tan⁻¹(-Eβ / Eα) (9) In this embodiment, the phase determiner 513 determines the rotational phase θ by performing calculations based on equation (9), but this is not limited to this. For example, the phase determiner 513 may determine the rotational phase θ by referring to a table stored in ROM 151b or the like that shows the relationship between induced voltages Eα and Eβ and the corresponding rotational phase θ'.

[0055] The rotational phase θ of the rotor 402 obtained as described above is output to the subtractor 101, the inverse coordinate converter 505, and the coordinate converter 511.

[0056] The motor control device 157 repeatedly performs the above-described control.

[0057] As described above, the motor control device 157 in this embodiment performs vector control using phase feedback control, which controls the current value in the rotating coordinate system so that the deviation between the command phase θ_ref and the rotation phase θ is small. By performing vector control, it is possible to suppress the motor losing synchronization, the increase in motor noise due to excess torque, and the increase in power consumption.

[0058] <torque detector> The torque detector 520 is described below. In this embodiment, the load torque applied to the motor can be determined with greater accuracy by applying the following configuration.

[0059] As shown in Figure 4, the motor control device 157 has a torque detector 520. 。 The torque detector 520 receives the current value iq, the induced voltages Eα and Eβ, and the rotational phase θ as input.

[0060] Figure 5 is a block diagram showing the configuration of the torque detector 520. As shown in Figure 5, the torque detector 520 includes a coordinate converter 601, a speed determiner 602, a divider 603, a torque constant memory 604, and a multiplier 606.

[0061] The coordinate converter 601 uses the input induced voltages Eα, Eβ and rotation phase θ to determine the q-axis component Eq of the induced voltage based on the following equation (10). Eq = -sinθ*Eα + cosθ*Eβ (10) The speed determination unit 602 determines the rotational speed ω based, for example, on the time change of the rotational phase θ. Alternatively, the speed determination unit 602 may calculate and output a speed ω_ref corresponding to the target speed of the rotor based on the time change of the command phase θ_ref. In other words, the speed determination unit 602 only needs to be configured to calculate a value corresponding to the rotational speed of the rotor.

[0062] To divider 603 at Eq component of induced voltage is round Rolling speed ω in The result is divided and output as the torque constant Kt to the torque constant memory 604.

[0063] The torque constant memory 604 stores the input torque constant Kt.

[0064] The multiplier 606 calculates and outputs the load torque T by multiplying the current value iq by the torque constant Kt output from the switch 605.

[0065] Figure 6 is a timing chart showing the timing for determining (acquiring) the torque constant Kt when transporting cardboard with a higher basis weight than ordinary paper. In the following explanation, as an example, a configuration in which the motor 509 drives the roller provided during the fixing phase 318 will be described.

[0066] The amount of heat required to fix an image onto cardboard is greater than the amount of heat required to fix an image onto plain paper. Therefore, in this embodiment, when an image is formed on cardboard, the speed at which the cardboard is transported is slower than the speed at which plain paper is transported.

[0067] As shown in Figure 6, in this embodiment, when the power supply of the image forming apparatus 100 is turned on from the off state, the motor control device 157 performs an initial operation to rotate the motor 509 at a first speed (or a third speed that is slower than the first speed and faster than the second speed). The torque detector 520 determines the torque constant Kt during the initial operation using the method described above. The torque constant memory 604 stores the input torque constant Kt. The first speed is, for example, the speed at which plain paper is transported, and is a speed at which the torque constant Kt can be determined with relatively high accuracy.

[0068] Subsequently, when an instruction to start an image formation job to form an image on the recording medium is input to the CPU 151a, the motor control device 157 rotates the motor 509 at a second speed. The second speed is, for example, the speed at which cardboard is transported, and is a speed at which the accuracy of determining the torque constant Kt is relatively low.

[0069] The torque detectors 520, corresponding to the first, second, and third determination units, do not determine the torque constant Kt during the period when the motor 509 is driven at the second speed. Furthermore, during the image forming job in which an image is formed on cardboard (during the period when the motor 509 is driven at the second speed), the torque detectors 520 determine the torque T based on the torque constant Kt stored in the torque constant memory 604, at the same period as the period in which the current value iq, induced voltages Eα and Eβ, and rotational phase θ are input.

[0070] In this embodiment, during an image formation job (printing job), an image adjustment operation is performed each time an image is formed on a predetermined number of sheets of cardboard. The image adjustment operation involves creating an image of a toner patch and reading it with a sensor to perform color misalignment correction, density correction, etc., while the motor rotation speed is the same high speed as for plain paper. By performing this operation in synchronization with the timing, the operation time required to acquire the torque constant Kt can be reduced, thereby suppressing a decrease in productivity.

[0071] The torque detector 520 determines the torque constant Kt when an image adjustment operation is performed. That is, in this embodiment, the torque constant Kt is updated each time an image adjustment operation is performed during an image forming job (printing job) on cardboard. As a result, torque calculation errors caused by changes in the torque constant due to motor temperature can be reduced.

[0072] Figure 7 is a timing chart showing the timing for determining (acquiring) the torque constant Kt when plain paper is being transported.

[0073] As shown in Figure 7, in this embodiment, when an instruction to start an image forming job to form an image on plain paper is input to the CPU 151a, the motor control device 157 rotates the motor 509 at a first speed.

[0074] The torque detector 520 determines the torque constant Kt each time the current value iq, induced voltages Eα and Eβ, and rotational phase θ are input during a plain paper image forming job (printing job). Furthermore, the torque detector 520 determines the torque T at the same frequency as the input period for the current value iq, induced voltages Eα and Eβ, and rotational phase θ. As a result, torque calculation errors caused by changes in the torque constant due to motor temperature can be reduced.

[0075] <Life detection based on Torque T> Figure 8 shows the relationship between the number of images formed (number of prints) and the torque of the motor 509. It can be seen that the load torque of the motor 509 increases as the number of prints increases. This phenomenon occurs because the rollers slide against each other in the nip section of the fuser 318, causing the rollers to wear down.

[0076] In this embodiment, for example, when the torque T detected by the torque detector 520 exceeds the threshold Tth1, the CPU 151a sends information to the server managing the operating status indicating that the fuser 318 is nearing the end of its lifespan. Service personnel then perform maintenance according to a plan based on this information. Downtime can be reduced by replacing the fuser unit according to a plan during regular maintenance rather than having service personnel called in to perform maintenance only when the fuser unit has reached the end of its lifespan and is unusable.

[0077] Furthermore, if the torque T detected by the torque detector 520 exceeds the threshold Tth2, the CPU 151a stops each load of the image forming apparatus 100 and notifies the user of an error indicating that maintenance is required via the display unit provided on the operation unit 152. By preventing excessive torque from being applied to drive transmission components such as gears, failure of drive transmission components can be prevented, and the number of parts requiring maintenance can be reduced.

[0078] As described above, in this embodiment, when image formation is performed on cardboard, the torque T is determined based on the torque constant Kt determined when the power of the image forming apparatus 100 is turned ON. Also, when image formation is performed on plain paper, , electric The torque constant Kt is determined each time the current value iq, induced voltages Eα and Eβ, and rotational phase θ are input. As a result, the load torque applied to the motor can be determined with greater accuracy.

[0079] In this embodiment, the motor 509 is controlled by phase feedback control, but the invention is not limited to this. For example, the motor 509 may be controlled by feeding back the rotational speed ω of the rotor 402. Specifically, as shown in Figure 9, a speed controller 500 is provided inside the motor control device, and the CPU 151a outputs a command speed ω_ref representing the target speed of the rotor. In addition, a speed determiner 514 is provided inside the motor control device, and the speed determiner 514 determines the rotational speed ω based on the time change of the rotational phase θ output from the phase corrector 520. The speed controller 500 is configured to generate and output a q-axis current command value iq_ref and a d-axis current command value id_ref so as to minimize the deviation between the rotational speed ω and the command speed ω_ref. The motor 509 may be controlled by such speed feedback control.

[0080] Furthermore, although a stepping motor is used as the motor to drive the load in this embodiment, other motors such as DC motors may also be used. Also, the motor is not limited to a two-phase motor, but may be other motors such as a three-phase motor.

[0081] Furthermore, while a permanent magnet is used as the rotor in this embodiment, the invention is not limited to this. [Explanation of Symbols]

[0082] 151a CPU 157 Motor control device 318 Fuser 402 Rotor 507, 508 Current detectors 509 Stepping motor 513 Phase determiner 520 Torque sensor

Claims

1. In an image forming apparatus equipped with image forming means for forming an image on a recording medium, A transport unit for transporting the recording medium, A motor that drives the transport unit, A detection means for detecting the drive current flowing through the windings of the motor, A phase determination means that determines the rotational phase of the motor rotor based on the drive current detected by the detection means, Control means for performing vector control of the rotation of the motor based on a torque current component, which is a current component that generates torque in the rotor and is represented in a rotating coordinate system based on the rotational phase determined by the phase determination means, and an excitation current component, which is a current component that affects the strength of the magnetic flux passing through the winding and is represented in the rotating coordinate system; A voltage determination means that determines the magnitude of the induced voltage induced in the winding by the rotation of the rotor, based on the drive current detected by the detection means, A first determination means for determining a torque constant based on the rotational phase determined by the phase determination means and the magnitude of the induced voltage determined by the voltage determination means, A second determination means determines the load torque applied to the rotor based on the value of the torque current component of the drive current detected by the detection means and the torque constant determined by the first determination means. It has, The control means rotates the motor at a first speed when an image is formed on a first recording medium having a first basis weight, and rotates the motor at a second speed slower than the first speed when an image is formed on a second recording medium having a second basis weight greater than the first basis weight. When the power supply of the image forming apparatus is turned on from an off state, the control means performs an initial operation to rotate the motor at a third speed greater than the second speed. The first determination means determines the torque constant based on the rotational phase determined by the phase determination means and the magnitude of the induced voltage determined by the voltage determination means during the initial operation. The second determination means determines the load torque based on the torque constant determined based on the rotation phase and the magnitude of the induced voltage, which were determined when the motor was rotating at the third speed during the initial operation, if an image is formed on the second recording medium. The image forming apparatus is characterized in that, when an image is formed on the first recording medium, the second determination means determines the load torque based on the torque constant determined based on the rotation phase determined by the phase determination means and the magnitude of the induced voltage determined by the voltage determination means while the motor is rotating at the first speed for transporting the first recording medium.

2. The image forming apparatus according to claim 1, further comprising a third determination means for determining the lifespan of the transport unit based on the load torque determined by the second determination means.

3. The image forming apparatus according to claim 1 or 2, characterized in that the third speed is the first speed.

4. The image forming apparatus according to any one of claims 1 to 3, characterized in that the control means controls the rotation of the motor so that the deviation between the target value of the torque current component, which is set 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 is small, and the value of the torque current component of the drive current detected by the detection means is small.

5. The image forming apparatus has a speed determination means for determining the rotational speed of the rotor, The image forming apparatus according to any one of claims 1 to 3, characterized in that the control means controls the rotation of the motor so as to reduce the deviation between a target value of the torque current component, which is set so as to reduce the deviation between the rotation speed determined by the speed determination means and a command speed representing the target speed of the rotor, and the value of the torque current component of the drive current detected by the detection means.

6. The image forming apparatus according to claim 1 or 2, wherein the control means, when an image is formed on the second recording medium, rotates the motor at the first speed after each predetermined number of image formations to form a measurement image and performs an adjustment operation to read the measurement image, and determines the load torque based on the torque constant determined based on the rotation phase determined by the phase determination means and the magnitude of the induced voltage determined by the voltage determination means during the adjustment operation.

7. The image forming apparatus according to claim 1 or 2, characterized in that when an image is formed on the first recording medium, the control means determines the load torque based on the torque constant determined based on the rotation phase determined by the phase determination means and the magnitude of the induced voltage determined by the voltage determination means each time the torque current component is acquired.

Images