Motor control device and image forming apparatus

Abstract

To provide a motor control technique to prevent a failure in starting a motor.SOLUTION: A motor control unit comprises a motor that drives a load, and control means that controls the motor. When staring the motor, the control means determines if a predetermined condition for determining that a variation in the magnitude of the load occurs is satisfied, when the predetermined condition is satisfied, starts the motor in a first mode, and when the predetermined condition is not satisfied, starts the motor in a second mode. The first mode is a mode in which the rotation speed of the motor increases gently compared to the second mode.SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0001] The present invention relates to a motor control technique. [Background technology]

[0002] Image forming apparatuses use sensorless motors (hereinafter referred to as sensorless motors) as their drive sources. When starting a sensorless motor, a motor control device first detects the rotor's stop position (rotational phase of the stopped rotor) using a predetermined method. Patent Document 1 discloses a configuration for detecting the rotor's stop position by utilizing the characteristic that the inductance value of the motor's coil changes depending on the rotor's stop position. The motor control device starts driving the motor using forced commutation control based on the detected rotor stop position. When the rotor's rotational speed reaches a predetermined speed or higher, the motor control device can detect the rotor's rotational position and rotational speed based on the induced voltage generated in the coil, as described in Patent Document 2. Therefore, after the rotor's rotational speed reaches a predetermined speed or higher, the motor control device switches from forced commutation control to sensorless control, which controls rotor rotation based on the induced voltage generated in the coil. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-104263 [Patent Document 2] Japanese Patent Application Publication No. 8-223970 Summary of the Invention [Problem to be solved by the invention]

[0004] The load on a motor can change for various reasons. For example, assume that the load is a photosensitive drum. In this case, the load can vary depending on the friction between the photosensitive drum and a cleaning blade that removes residual toner from the photosensitive drum. Furthermore, if the load is replaced, the load can fluctuate before and after replacement. Forced commutation control uses a predetermined current value to control the motor, so if the load torque is greater than the output torque obtained with that predetermined current value, startup problems such as loss of synchronization can occur.

[0005] The present invention provides a motor control technique that suppresses motor start-up failures. [Means for solving the problem]

[0006] According to one aspect of the present invention, a motor control device includes a motor that drives a load and control means that controls the motor, wherein when starting the motor, the control means determines whether a predetermined condition for determining that a fluctuation in the magnitude of the load has occurred is satisfied, and starts the motor in a first mode if the predetermined condition is satisfied, and starts the motor in a second mode if the predetermined condition is not satisfied, when starting the motor in the first mode, the control means accelerates the motor at a first acceleration using forced commutation control until the rotational speed of the motor reaches a predetermined value, and when the rotational speed of the motor reaches the predetermined value, maintains the rotational speed of the motor constant and switches control of the motor from the forced commutation control to sensorless control based on an induced voltage generated in the motor, and after switching control of the motor from the forced commutation control to the sensorless control, accelerates the motor again at a second acceleration until the rotational speed of the motor, which is rotating at a constant speed, reaches a target value, and when starting the motor in the second mode, accelerates the motor at a third acceleration greater than the first acceleration using forced commutation control, and when the rotational speed of the motor reaches a threshold value or more, switches control of the motor from the forced commutation control to the sensorless control. It is characterized by: [Effects of the Invention]

[0007] According to the present invention, it is possible to suppress starting failure of the motor. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a diagram illustrating the configuration of an image forming apparatus according to an embodiment. [Figure 2] FIG. 2 is a configuration diagram of a motor control unit according to an embodiment. [Figure 3] FIG. 1 is a configuration diagram of a motor according to an embodiment. [Figure 4] FIG. 2 is a functional block diagram of a microcomputer during forced commutation control according to an embodiment. [Figure 5] FIG. 2 is a functional block diagram of a microcomputer during sensorless control according to an embodiment. [Figure 6]1 is a diagram illustrating a motor starting method according to an embodiment. [Figure 7] FIG. 10 is a diagram showing an example of information used to determine the startup mode to be used. [Figure 8] 10 is a flowchart of booting in normal mode according to one embodiment. [Figure 9] 10 is a flowchart of a high torque mode start-up according to one embodiment. [Figure 10] 4 is a time chart showing a start-up time of a motor according to an embodiment. [Figure 11] 10 is a flowchart of booting in normal mode according to one embodiment. [Figure 12] 10 is a flowchart of a high torque mode start-up according to one embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, embodiments will be described in detail with reference to the accompanying drawings. Note that the following embodiments do not limit the scope of the invention claimed. Although multiple features are described in the embodiments, not all of these multiple features are necessarily essential to the invention, and multiple features may be combined arbitrarily. Furthermore, in the accompanying drawings, the same reference numerals are used to designate the same or similar components, and redundant explanations will be omitted.

[0010] First Embodiment FIG. 1 is a diagram illustrating the configuration of a tandem-type color image forming apparatus using an electrophotographic process according to this embodiment. In FIG. 1, the letters Y, M, C, and K at the end of a reference number indicate the color of the toner image formed by the component designated by the reference number: yellow, magenta, cyan, and black, respectively. Note that when it is not necessary to distinguish the color of the toner image formed by the component, the reference number is used without the letter at the end. The image forming apparatus includes cartridges 12. The cartridges 12 are replaceable parts for the image forming apparatus and are configured to be detachable from the main body of the image forming apparatus. Each cartridge 12 has the same configuration, including a photoconductor 13, a charging roller 15, a developing roller 16, and a cleaning blade 14, and contains toner of the corresponding color.

[0011] During image formation, the photoconductors 13 are rotated clockwise in the figure. The charging rollers 15 charge the surfaces of the corresponding photoconductors 13. The scanning unit 11 scans and exposes the surfaces of the photoconductors 13 of the corresponding cartridges 12 with light based on image data, forming electrostatic latent images on the photoconductors 13. The developing rollers 16 output a development voltage to develop the electrostatic latent images on the corresponding photoconductors 13 with toner, thereby forming toner images on the corresponding photoconductors 13. The primary transfer rollers 18 output a primary transfer voltage to transfer the toner images on the corresponding photoconductors 13 to the intermediate transfer belt 19. The cleaning blade 14 removes toner remaining on the photoconductors 13 that was not transferred to the intermediate transfer belt 19. By transferring the toner images on the photoconductors 13 of the respective cartridges 12 onto the intermediate transfer belt 19 in layers, it is possible to reproduce colors different from yellow, magenta, cyan, and black. The intermediate transfer belt 19 is rotated counterclockwise in the figure during image formation. As a result, the toner image on the intermediate transfer belt 19 is conveyed to a position facing the secondary transfer roller 29 .

[0012] Meanwhile, the sheet 21 stored in the cassette 22 is fed to the conveying path by a feed roller 25. Separation rollers 26a and 26b are provided to prevent double feeding of sheets. The sheet 21 fed to the conveying path is transported by a registration roller 27 to a position facing a secondary transfer roller 29. The secondary transfer roller 29 outputs a secondary transfer voltage to transfer the toner image on the intermediate transfer belt 19 to the sheet 21. The sheet 21 is then transported to a fixing unit 30. The fixing unit 30 has a pressure roller and a heating roller (heating film), and fixes the toner image to the sheet 21 by applying pressure and heat to the sheet 21. After the toner image is fixed, the sheet 21 is discharged outside the image forming apparatus.

[0013] The printer control unit 107 has a CPU (Central Processing Unit) 32 and controls the entire image forming apparatus. The printer control unit 107 has a non-volatile memory 32a that stores control programs executed by the CPU 32 and control data used by the CPU 32 to control the image forming apparatus. The printer control unit 107 also has a volatile memory 32b that the CPU 32 uses as a work area when controlling the image forming apparatus. The image forming apparatus also has one or more sensorless motors (not shown in FIG. 1) for driving rollers for conveying the sheet 21, such as the photoconductor 13, the intermediate transfer belt 19, the developing roller 16, the pressure roller of the fixing unit 30, and the registration roller 27. In the following description, the sensorless motor will be simply referred to as a "motor."

[0014] 2 shows the control configuration of the motor 103 provided in the image forming apparatus. The motor control unit 110 communicates with the printer control unit 107 and controls the motor 103 under the control of the printer control unit 107. The nonvolatile memory 205 of the microcomputer (MCU) 201 stores programs executed by the MCU 201 and various data used to control the motor 103. The memory 207 is used by the MCU 201 for temporary data storage. The PWM port 208 has a total of six terminals for outputting two PWM signals (high side, low side) for each of the three phases (U, V, W) of the motor 103. That is, the PWM port 208 has three high-side terminals (UH, VH, WH) and three low-side terminals (UL, VL, WL).

[0015] The inverter 211 has high-side switching elements M1, M3, and M5 and low-side switching elements M2, M4, and M6 for each of the three phases of the motor 103. In FIG. 2, M1 and M2 are U-phase switching elements, M3 and M4 are V-phase switching elements, and M5 and M6 are W-phase switching elements. The switching elements may be, for example, transistors or FETs. The gate driver 210 controls the ON / OFF of the corresponding switching element based on a PWM signal from the PWM port 208. For example, the gate driver 210 controls the ON / OFF of the switching element M1 by controlling the voltage applied to the gate G1 of the switching element M1 based on the PWM signal output from the UH terminal.

[0016] The U-, V-, and W-phase outputs 217 of the inverter 211 are connected to coils 213 (U-phase), 214 (V-phase), and 215 (W-phase) of the motor 103. By controlling the ON / OFF of each switching element, the coil current flowing through each of the coils 213, 214, and 215 can be controlled. In this manner, the inverter 211 functions as a current supply unit that supplies the coil current to each of the coils 213, 214, and 215. The coil current flowing through each of the coils 213, 214, and 215 is converted into a voltage by current detection resistors 219, 220, and 221. An amplifier 218 amplifies the voltage of the current detection resistors 219, 220, and 221, which corresponds to the coil current, and outputs the amplified voltage to an AD converter 203 of the microcomputer 201. The AD converter 203 converts the voltage output by the amplifier 218 into a digital value. The current value calculation unit 209 determines the current value of the coil current of each phase based on the digital value output by the AD converter 203 .

[0017] FIG. 3 is a configuration diagram of the motor 103. The motor 103 has a six-slot stator 501 and a four-pole rotor 502. The stator 501 has a U-phase coil 213, a V-phase coil 214, and a W-phase coil 215. The rotor 502 is formed of a permanent magnet. The rotational phase of the rotor 502 is defined based on a state in which the rotor 502 is in a predetermined state. As an example, as shown in FIG. 3, the state in which the south pole of the rotor 502 faces the U-phase coil 213 is defined as a reference, that is, an electrical angle of 0, and the electrical angle can be defined as increasing in the counterclockwise direction. In this embodiment, the number of poles of the rotor 502 is four, so when the rotor rotates counterclockwise by a mechanical angle of π / 2 from the state in FIG. 3, the electrical angle becomes π.

[0018] 4 is a functional block diagram of the microcomputer 201 during forced commutation control. In this embodiment, the microcomputer 201 performs vector control of the motor 103. The current control unit 302 acquires an excitation current command value Id_ref and a torque current command value Iq_ref, which are pre-stored in the nonvolatile memory 205. The current control unit 302 also receives a measured excitation current value Id and a measured torque current value Iq from the coordinate conversion unit 306. The excitation current is a component of the coil current that contributes to the generation of magnetic flux, and the torque current is a component of the coil current that contributes to output torque. Based on these values, the current control unit 302 outputs voltage command values ​​Vd_ref and Vq_ref in a rotating coordinate system. The coordinate conversion unit 305 performs coordinate conversion from the rotating coordinate system to a stationary coordinate system, and further performs two-phase-to-three-phase conversion to generate and output voltage command values ​​Vu, Vv, and Vw for the U-phase, V-phase, and W-phase from the voltage command values ​​Vd_ref and Vq_ref. Note that the coordinate conversion from the rotating coordinate system to the stationary coordinate system is performed based on the electrical angle θ_ref output from the angle calculation unit 303. The microcomputer 201 generates PWM signals to be output to the gate driver 210 based on the voltage command values ​​Vu, Vv, and Vw.

[0019] Furthermore, the current values ​​Iu, Iv, and Iw of the coil currents of the U phase, V phase, and W phase detected by the current value calculation unit 209 based on the output of the amplifier 218 are input to a coordinate conversion unit 306. The coordinate conversion unit 306 converts the current values ​​Iu, Iv, and Iw into current values ​​in a stationary coordinate system by three-phase-two-phase conversion, and further performs coordinate conversion from the stationary coordinate system to a rotating coordinate system to obtain a measured value Id of the excitation component current and a measured value Iq of the torque component current. The coordinate conversion from the stationary coordinate system to the rotating coordinate system is performed based on the electrical angle θ_ref output from the angle calculation unit 303. The coordinate conversion unit 306 outputs the measured value Id of the excitation component current and the measured value Iq of the torque component current to the current control unit 302.

[0020] When the motor 103 is started, the detection unit 301 determines the initial phase of the rotor 502, i.e., the electrical angle at the time of stopping (hereinafter referred to as the stop angle) θ_std. The detection of the electrical angle at the time of stopping the rotor 502 can be performed using, for example, the configuration described in Patent Document 1. In this case, the detection unit 301 detects the stop angle θ_std by detecting the inductance of each of the coils 213, 214, and 215 based on the current values ​​Iu, Iv, and Iw. The detection unit 301 outputs the detected stop angle θ_std to the subtractor 307. The offset setting unit 304 outputs the offset amount Δ stored in the nonvolatile memory 205 to the subtractor 307. The subtractor 307 outputs the electrical angle obtained by subtracting the offset amount Δ from the stop angle θ_std as the initial angle θ_ini to the angle calculation unit 303. Note that the electrical angle obtained by subtracting the offset amount Δ from the stop angle θ_std is set as the initial angle θ_ini in order to prevent loss of synchronism during start-up.

[0021] The angle calculation unit 303 calculates the electrical angle θ_ref of the rotor 502 based on the initial angle θ_ini and the speed command value ω_ref input from the printer control unit 107, and notifies the coordinate conversion units 305 and 306. Specifically, the angle calculation unit 303 calculates the electrical angle θ_ref of the rotor 502 by setting the initial angle θ_ini as an initial value and increasing the electrical angle based on the speed command value ω_ref.

[0022] FIG. 5 is a functional block diagram of the microcomputer 201 during sensorless control. The following description will focus on differences from the functional block diagram during forced commutation control shown in FIG. 4. An estimator 801 estimates the electrical angle θ_est and rotational speed ω_est of the rotor 502 based on the current values ​​Iu, Iv, and Iw, voltage command values ​​Vd_ref and Vq_ref, and the estimated rotational speed ω_est. The estimated electrical angle θ_est is used for coordinate conversion in the coordinate converters 305 and 306, as in the case of forced commutation control. Furthermore, a speed controller 802 calculates a command value Iq_ref for causing the rotational speed ω_est to follow the speed command value ω_ref, based on the speed command value ω_ref from the printer controller 107 and the rotational speed ω_est estimated by the estimator 801. Unlike forced commutation control, the speed control unit 802 calculates the command value Iq_ref and outputs it to the current control unit 302, so the current control unit 302 obtains only the command value Id_ref from the nonvolatile memory 205 and uses it.

[0023] FIG. 6A shows the speed change of the motor 103 when the motor 103 is started. The dotted line indicates the time change of the speed command value ω_ref. The motor control unit 110 starts rotating the motor 103 using forced commutation control. Then, for example, at time Ta when the speed command value ω_ref reaches a threshold value, the motor control unit 110 switches the motor control from forced commutation control to sensorless control. Note that sensorless control is applicable when the rotation speed of the motor 103 is equal to or higher than the threshold value. Thereafter, the speed command value ω_ref increases to the target value and becomes constant at the target value. After time Ta, the motor control unit 110 performs sensorless control of the motor 103 in accordance with the speed command value ω_ref. FIG. 6B shows a case where the start of the motor 103 fails because the load on the motor 103 becomes too large due to a load fluctuation of the motor 103. In the case of a motor with a Hall element, even if the load becomes heavy, the speed change at start-up only becomes gradual. However, in forced commutation control for a motor 103 without a Hall element, if the load torque exceeds the output torque of the motor 103, the motor 103 will lose synchronization. The output torque of the motor 103 during forced commutation control is determined by the coil current during forced commutation control, i.e., the excitation current command value Id_ref and the torque current command value Iq_ref. As explained using FIG. 4, the excitation current command value Id_ref and the torque current command value Iq_ref during forced commutation control are predetermined values ​​stored in advance in the non-volatile memory 205. The load torque of the motor 103 is the sum of the acceleration torque for accelerating the rotor 502 and the steady torque required to rotate the motor 103 at a constant speed.

[0024] FIG. 6(C) shows the speed change of the motor 103 when the rate of increase of the speed command value ω_ref is slower than in FIGS. 6(A) and 6(B). As shown in FIG. 6(C), by controlling the acceleration of the motor 103 to be smaller than in FIGS. 6(A) and 6(B), the acceleration torque is reduced, and it is possible to prevent the sum of the acceleration torque and the steady-state torque from exceeding the output torque, resulting in loss of synchronization. Also, in FIG. 6(C), acceleration is stopped for a predetermined time when switching to sensorless control. When switching from forced commutation control to sensorless control, the control of the motor 103 may become unstable. However, the risk of startup failure can be reduced by switching with the acceleration torque set to approximately zero. Note that starting up as shown in FIG. 6(C) reduces the risk of loss of synchronization compared to starting up as shown in FIGS. 6(A) and 6(B). However, it takes longer for the rotational speed of the motor 103 to reach the target speed, i.e., it takes longer for the startup of the motor 103 to be completed.

[0025] In the following explanation, the load on the motor 103 is the photoreceptor 13. First, the load torque of the photoreceptor 13 will be explained. As described above, a cleaning blade (photoreceptor cleaner) 14 is provided to remove residual toner from the photoreceptor 13. As the frictional force between the cleaning blade 14 and the photoreceptor 13 increases, the torque required to rotate the photoreceptor 13 increases. Therefore, the load torque of the motor 103 changes depending on the surface condition of the photoreceptor 13 and the state of the toner present between the photoreceptor 13 and the cleaning blade 14. For example, if no printing is performed for a long period of time, the surface condition of the photoreceptor 13 may change, and the frictional force between the photoreceptor 13 and the cleaning blade 14 may increase. Therefore, if the printer is started as shown in FIG. 6A after being left unused for a long period of time, a startup failure may occur.

[0026] For this reason, this embodiment provides multiple startup modes. In the following description, the basic startup mode shown in FIG. 6(A) will be referred to as the "normal mode." On the other hand, as shown in FIG. 6(C), a startup mode in which the speed of the motor 103 increases more slowly than in the basic mode, thereby enabling startup even under heavy (large) loads, will be referred to as the "high torque mode." The normal mode has a shorter startup time (time required to reach the target speed) than the high torque mode, but is more likely to cause startup failure when the load becomes heavy. Conversely, the high torque mode has a longer startup time than the normal mode, but is less likely to cause startup failure even under heavy loads.

[0027] When starting the motor 103, the printer control unit 107 determines whether the load state satisfies a predetermined condition for determining that a fluctuation in load magnitude has occurred. If the predetermined condition is satisfied, the printer control unit 107 sets the motor to high-torque mode; otherwise, it sets the motor to normal mode. FIG. 7 shows examples of the predetermined conditions. The information shown in FIG. 7 is pre-stored in the non-volatile memory 32a of the printer control unit 107. As shown in FIG. 7, the high-torque mode is used after a predetermined period of inactivity, i.e., when starting the motor 103, if the stop time up to that point is longer than the predetermined period of time. Furthermore, when starting the motor for the first time after replacing the cartridge 12, the high-torque mode is used because the load torque may be heavy. Note that replacing the cartridge 12 includes replacing it with a new cartridge 12 and replacing it with a cartridge 12 that has already been used. The predetermined condition for determining whether to use the high-torque mode is a condition for determining whether the load torque is fluctuating, more specifically, whether the load may be heavier (larger) than a reference value, and may include conditions other than those shown in FIG. 7. The acceleration of the motor 103 at startup in normal mode can be determined based on a reference load value. The printer control unit 107 sets the startup mode to the high torque mode when predetermined conditions for using the high torque mode are met, and sets the startup mode to the normal mode when the predetermined conditions are not met.

[0028] 8 is a flowchart of the motor startup process when the normal mode is set. In S10, the motor control unit 110 performs forced commutation control on the motor 103 at acceleration X. That is, the printer control unit 107 increases the speed command value ω_ref in accordance with the acceleration X. When the speed command value ω_ref becomes equal to or greater than the threshold value Th in S11, the motor control unit 110 switches to sensorless control in S12. Thereafter, the printer control unit 107 accelerates the motor 103 at acceleration X toward the target speed, and when the speed command value ω_ref reaches the target value, the printer control unit 107 keeps the speed command value ω_ref constant at the target value.

[0029] FIG. 9 is a flowchart of the motor startup process when the high-torque mode is selected. In S20, the motor control unit 110 performs forced commutation control of the motor 103 using acceleration Y. That is, the printer control unit 107 increases the speed command value ω_ref according to acceleration Y. Note that acceleration Y is smaller than acceleration X used in normal mode. When the speed command value ω_ref reaches a predetermined value AV in S21, the printer control unit 107 stops acceleration in S22, i.e., maintains the speed command value ω_ref constant at the predetermined value AV. Note that the predetermined value AV is a value that enables sensorless control, i.e., a value equal to or greater than threshold Th. The motor control unit 110 waits for a period P1 in S23 and then switches to sensorless control in S24. Thereafter, the printer control unit 107 waits for a period P2 in S25 and then accelerates the motor 103 using acceleration Y toward the target speed in S26. When the speed command value ω_ref reaches the target value, the printer control unit 107 maintains the speed command value ω_ref constant at the target value. The period P1 and the period P2 may be the same or different periods. As an example, the period P1 and the period P2 are 100 milliseconds.

[0030] 9, the printer control unit 107 stopped acceleration when switching from forced commutation control to sensorless control (S22). As described above, this was done to reduce the load torque by setting the acceleration torque to approximately zero, since control can become unstable when switching from forced commutation control to sensorless control. However, instead of stopping acceleration, the configuration may be such that acceleration is changed to acceleration Z, which is smaller than acceleration Y, and the control is switched to sensorless control while accelerating at acceleration Z. Furthermore, the configuration may be such that the control is switched to sensorless control while acceleration Y is maintained.

[0031] Also, in the process of FIG. 9, after switching to sensorless control, the printer control unit 107 accelerates the motor 103 at acceleration Y. However, after switching to sensorless control, the motor 103 can be accelerated at an acceleration greater than acceleration Y, for example, acceleration X, the same as in normal mode. Furthermore, although acceleration X is used in normal mode and acceleration Y is used in high torque mode, the present invention is not limited to accelerating the motor 103 at a constant acceleration. In other words, acceleration X and acceleration Y may be functions of time. In this case, the maximum value of acceleration Y may be configured to be smaller than the maximum value of acceleration X. Alternatively, the maximum value of acceleration Y may be configured to be smaller than the minimum value or average value of acceleration X. Furthermore, the average value of acceleration Y may be configured to be smaller than the average value of acceleration X.

[0032] As described above, when it is determined that the load may be heavier than the reference value, the acceleration torque is reduced by slowing down the speed increase at startup compared to when it is determined that this is not the case. This configuration can reduce the occurrence of startup failures.

[0033] In this embodiment, the load of the motor 103 is the photoconductor 13. However, the present invention can be applied to the control of any motor whose load weight can vary, and the motor load is not limited to the photoconductor 13. Also, a condition for determining the load weight can be set, and if it is determined based on the condition that the load is heavier than a reference value, the high torque mode is used, and if not, the normal mode is used. Furthermore, a configuration can be adopted in which the load weight is determined, and if the load is heavier than a reference value, the high torque mode is used, and if not, the normal mode is used.

[0034] Second Embodiment Next, the second embodiment will be described, focusing on differences from the first embodiment. FIGS. 10A and 10B are timing charts for startup in normal mode. Time T0 in FIG. 10 corresponds to the timing at which the image forming apparatus receives a print job. FIG. 10A illustrates a case in which the fixing unit 30 is in a state where it is warmed to a certain degree at time T0 (hereinafter referred to as a warm state). On the other hand, FIG. 10B illustrates a case in which the fixing unit 30 is in a state where its temperature is lower than the warm state (hereinafter referred to as a cold state) at time T0. The printer control unit 107 can determine whether the fixing unit 30 is in a cold or warm state based on, for example, the measurement results of a temperature sensor provided in the fixing unit 30. Specifically, if the measurement results of the temperature sensor indicate a temperature higher than a predetermined temperature, the fixing unit 30 is determined to be in a warm state; otherwise, the fixing unit 30 is determined to be in a cold state. The printer control unit 107 can also determine whether the fixing unit 30 is in a cold or warm state based on the time elapsed since the completion of the previous print job. Specifically, if the time that has elapsed since the completion of the previous print job is longer than a predetermined time, the printer is determined to be in a warm state, and otherwise the printer is determined to be in a cold state.

[0035] When the printer control unit 107 receives a print job at time T0, it performs various preparation processes for image formation. This preparation process includes a fixing preparation process for raising the fixing unit 30 to a predetermined fixing temperature. That is, when the printer control unit 107 receives a print job, it starts temperature control of the fixing unit 30. When the warm-up of the fixing unit 30 is complete (fixing preparation is complete), the printer control unit 107 starts activating the motor 103. For example, the printer control unit 107 determines that fixing preparation is complete when the temperature of the fixing unit 30 reaches a predetermined temperature. Note that the predetermined temperature of the fixing unit 30 at which fixing preparation is complete can be lower than the fixing temperature at which the fixing unit 30 performs the fixing process. This is because it is sufficient that the fixing temperature is reached when the sheet onto which the toner image has been transferred reaches the fixing unit 30. Note that the predetermined temperature does not need to be a constant temperature. For example, the fixing temperature can be controlled depending on the type of sheet. Therefore, the predetermined temperature at which fixing preparation is complete can be determined based on the required fixing temperature.

[0036] In FIG. 10A, fixing preparation is completed at time T11, and therefore, printer control unit 107 starts activating motor 103 at time T11. Then, at time T12, activation of motor 103 is completed, i.e., the speed of motor 103 reaches the target speed. Printer control unit 107 starts image formation a predetermined period after activation of motor 103 is completed. In contrast, in FIG. 10B, since fixing unit 30 is in a cold state at time T0, the time until fixing preparation is completed is longer than in FIG. 10A, where fixing unit 30 is in a warm state. Fixing preparation is completed at time T21, which is after time T11. The time required for motor activation is the same as in FIG. 10A, but the time required for preparation of fixing unit 30 is longer than in FIG. 10A. Therefore, in FIG. 10B, time T22 at which activation of motor 103 is completed is later than in FIG. 10A. In this way, when the fixing unit 30 is in a cold state, the period from when the print job is received until when image formation can start becomes longer, and therefore the period from when the print job is received until when the sheet on which the image is formed is output also becomes longer. Note that the reason why the motor 103 is started after the fixing preparation is completed is to shorten the rotation time of the photoconductor 13 and extend the life of the photoconductor 13.

[0037] FIG. 10C is a timing chart showing the start of the motor 103 in high torque mode using the same sequence as in FIGS. 10A and 10B. It is assumed that the fixing unit 30 is in a cold state at time T0. The timing at which the fixing unit 30 is ready is time T21, as in FIG. 10B. However, because the acceleration of the motor 103 is lower in high torque mode than in normal mode, the start-up time of the motor 103 is longer than in normal mode. In FIG. 10C, the start-up of the motor 103 is completed at time T32, which is later than time T22. Therefore, the time from receiving a print job to starting image formation is longer than in FIG. 10B.

[0038] For this reason, in this embodiment, if the fixing unit 30 is in a cold state when a print job is received and activation of the motor 103 in high-torque mode is required, the printer control unit 107 starts activation of the motor 103 together with the start of fixing preparation, as shown in FIG. 10(D). In the example of FIG. 10(D), activation of the motor 103 is completed at time T42, which is earlier than time T32. Note that the difference between time T32 and time T42 corresponds to the difference between time T0 and time T21. This configuration allows the activation of the motor 103 to be completed earlier. Therefore, it is possible to prevent the period from receiving the print job to the timing at which image formation begins and the period from receiving the print job to the timing at which the image forming apparatus outputs a sheet with an image formed on it from being too long.

[0039] 11 and 12 are flowcharts of the processing executed by printer control unit 107 when a print job is received. Note that Fig. 11 shows the case where motor 103 is started in normal mode, and Fig. 12 shows the case where motor 103 is started in high torque mode. Note that the same step numbers are assigned to processing steps that are the same as those in the flowcharts of Figs. 8 and 9, and their explanations will be omitted.

[0040] When starting in normal mode, upon receiving a print job, the printer control unit 107 starts fixing preparation in S30 and waits until fixing preparation is complete. Once fixing preparation is complete, the printer control unit 107 performs the same processing as in the flowchart of FIG. 8. On the other hand, when starting in high torque mode, upon receiving a print job, the printer control unit 107 determines whether the fixing unit 30 is in a cold state in S40. If the fixing unit 30 is not in a cold state, the printer control unit 107 waits until fixing preparation is complete in S41, and once fixing preparation is complete, starts starting the motor 103 at acceleration Y in S20. On the other hand, if the fixing unit 30 is in a cold state in S40, the printer control unit 107 starts fixing preparation and starts starting the motor 103 at acceleration Y in S20.

[0041] Furthermore, the printer control unit 107 determines whether the fixing preparation is complete in S42 before S26, and after the fixing preparation is complete, accelerates the motor 103 again in S26. This is to prevent the motor 103 from being started and image formation from starting when the fixing preparation is not complete if the answer is Yes in S40.

[0042] In this embodiment, when the high torque mode is required and the fixing unit 30 is in a warm state when a print job is received, the motor 103 is started after waiting for the fixing preparation to be completed. However, in the high torque mode, the motor 103 can be configured to always start starting when the fixing preparation starts. Furthermore, in the high torque mode, the motor 103 can be configured to start starting by the time the fixing preparation is completed, rather than starting starting when the fixing preparation starts. In other words, in the high torque mode, the timing to start the motor 103 starting can be configured to be earlier than in the normal mode.

[0043] In addition, in this embodiment, the load of the motor 103 is the photosensitive member 13. However, this embodiment can also be applied to other loads whose start timing is controlled depending on the state of the fixing unit 30. For example, this embodiment can be applied to the case where the load is any member of the image forming unit, including the cartridge 12 that forms an image on a sheet and the intermediate transfer belt 19.

[0044] <Other> In the above embodiments, the motor control unit 110 is referred to as a single component of the image forming apparatus. However, the motor control unit 110 can also be referred to as a motor control device. Furthermore, a device including the printer control unit 107 and the motor control unit 110 can also be referred to as a motor control device. The present invention can also be applied to the control of motors that drive any component, such as motors that drive image forming units involved in image formation, such as the cartridge 12 and the intermediate transfer belt 19, or motors that drive rollers (rotating members) for transporting the sheet 21. For example, the load of the motor 103 can be one or more of the photoreceptor 13, the developing roller 16, the intermediate transfer belt 19, the pressure roller of the fixing unit 30, and the roller for transporting the sheet 21. Furthermore, the configuration of the motor 103 is not limited to the configuration shown in FIG. 3 , and a motor with a different number of poles and phases may be used. Furthermore, the high-torque mode can be configured in multiple stages depending on the estimated required output torque. For example, a first high-torque mode, a second high-torque mode, and a third high-torque mode can be provided. The first high-torque mode, the second high-torque mode, and the third high-torque mode each have different accelerations at startup.

[0045] [Other embodiments] The present invention can also be realized by supplying a program that realizes one or more functions of the above-described embodiments to a system or device via a network or a storage medium, and having one or more processors in the computer of the system or device read and execute the program.The present invention can also be realized by a circuit (e.g., ASIC) that realizes one or more functions.

[0046] The invention is not limited to the above-described embodiments, and various changes and modifications can be made without departing from the spirit and scope of the invention. Accordingly, the following claims are appended to apprise the public of the scope of the invention. [Explanation of symbols]

[0047] 103: Motor, 107: Printer control unit, 110: Motor control unit

Claims

1. a motor that drives a load; a control means for controlling the motor; A motor control device comprising: When starting the motor, the control means determines whether a predetermined condition for determining that a fluctuation in the magnitude of the load is occurring is satisfied, and starts the motor in a first mode if the predetermined condition is satisfied, and starts the motor in a second mode if the predetermined condition is not satisfied; The control means When starting the motor in the first mode, the motor is accelerated at a first acceleration by forced commutation control until the rotational speed of the motor reaches a predetermined value, and when the rotational speed of the motor reaches the predetermined value, the rotational speed of the motor is made constant and control of the motor is switched from the forced commutation control to sensorless control based on an induced voltage generated in the motor, and after control of the motor is switched from the forced commutation control to the sensorless control, the motor, which is rotating at a constant speed, is accelerated again at a second acceleration until the rotational speed of the motor reaches a target value, When starting the motor in the second mode, the motor is accelerated at a third acceleration greater than the first acceleration by the forced commutation control, and when the rotation speed of the motor becomes equal to or greater than a threshold, control of the motor is switched from the forced commutation control to the sensorless control.

2. a motor that drives a load; a control means for controlling the motor; a motor control device that starts the motor in a first mode or a second mode, a load torque of the motor in the first mode is greater than a load torque of the motor in the second mode; The control means When starting the motor in the first mode, the motor is accelerated at a first acceleration by forced commutation control until the rotational speed of the motor reaches a predetermined value, and when the rotational speed of the motor reaches the predetermined value, the rotational speed of the motor is made constant and control of the motor is switched from the forced commutation control to sensorless control based on an induced voltage generated in the motor, and after control of the motor is switched from the forced commutation control to the sensorless control, the motor, which is rotating at a constant speed, is accelerated again at a second acceleration until the rotational speed of the motor reaches a target value, When starting the motor in the second mode, the motor is accelerated at a third acceleration greater than the first acceleration by the forced commutation control, and when the rotation speed of the motor becomes equal to or greater than a threshold, control of the motor is switched from the forced commutation control to the sensorless control.

3. A motor control device as described in claim 1 or 2, wherein the specified value is equal to or greater than the threshold value.

4. 2. The motor control device according to claim 1, wherein the predetermined condition is satisfied when the motor is started if the time the motor has been stopped up to that time is greater than a predetermined time.

5. The motor control device according to claim 1 , wherein the predetermined condition is satisfied when the motor is started for the first time since the load of the motor has been replaced.

6. 6. The motor control device according to claim 1, wherein the motor is a sensorless motor that does not have a sensor for detecting the rotational position of a rotor.

7. 7. The motor control device according to claim 1, wherein the load includes at least one of a photosensitive member of an image forming device, a developing roller that forms a toner image on the photosensitive member by developing an electrostatic latent image formed on the photosensitive member, an intermediate transfer belt onto which the toner image formed on the photosensitive member is transferred, a roller that fixes the toner image transferred from the intermediate transfer belt onto a sheet, and a roller for transporting the sheet.

8. a rotating member for transporting the sheet along the transport path; an image forming means for forming an image on the sheet conveyed through the conveying path; a motor that drives the rotating member or the image forming means; a control means for determining whether a predetermined condition for determining that a fluctuation in the magnitude of the load on the motor has occurred is satisfied when the motor is started, and for starting the motor in a first mode if the predetermined condition is satisfied, and for starting the motor in a second mode if the predetermined condition is not satisfied; Equipped with The control means When starting the motor in the first mode, the motor is accelerated at a first acceleration by forced commutation control until the rotational speed of the motor reaches a predetermined value, and when the rotational speed of the motor reaches the predetermined value, the rotational speed of the motor is made constant and control of the motor is switched from the forced commutation control to sensorless control based on an induced voltage generated in the motor, and after control of the motor is switched from the forced commutation control to the sensorless control, the motor, which is rotating at a constant speed, is accelerated again at a second acceleration until the rotational speed of the motor reaches a target value, When the motor is started in the second mode, the motor is accelerated at a third acceleration greater than the first acceleration by the forced commutation control, and when the rotation speed of the motor reaches or exceeds a threshold, control of the motor is switched from the forced commutation control to the sensorless control.

9. a fixing unit for fixing the image formed on the sheet by the image forming unit, the motor drives the image forming means, 9. The image forming apparatus according to claim 8, wherein the control means starts temperature control of the fixing means when a print job is received, and if the predetermined condition is not satisfied when the print job is received, starts the motor in the second mode at a first timing after starting the temperature control, and if the predetermined condition is satisfied when the print job is received, starts the motor in the first mode at a second timing before the first timing.

10. 10. The image forming apparatus according to claim 9, wherein the second timing is a timing at which temperature control of the fixing unit is started.

11. 11. The image forming apparatus according to claim 9, wherein the control unit determines the state of the fixing unit when the print job is received, and if the predetermined condition is satisfied and the state of the fixing unit is in a first state, starts the motor in the first mode at the second timing.

12. 12. The image forming apparatus according to claim 11, wherein the control unit starts the motor in the first mode at a third timing after the second timing when the predetermined condition is satisfied and the fixing unit is in a second state different from the first state upon receiving the print job.

13. 13. The image forming apparatus according to claim 12, wherein the fixing unit in the first state is in a state where the temperature of the fixing unit is lower than that of the fixing unit in the second state.

14. 14. The image forming apparatus according to claim 9, wherein the first timing is a timing at which the temperature of the fixing unit reaches a predetermined temperature.

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