Motor control device and image forming apparatus

Abstract

To provide a technique for stably starting a motor.SOLUTION: A motor control device includes: current supply means for supplying a coil current to a plurality of coils by controlling a voltage to be applied to the plurality of coils of a motor based on a first command value of an excitation current and a second command value of a torque current; first setting means for setting the first command value; second setting means for setting the second command value; and control means for using first control when rotation of a rotor of the motor is started, and switching to second control after rotation speed of the rotor becomes larger than predetermined speed. The first setting means sets a value larger than zero as the first command value before the control means switches from the first control to the second control.SELECTED DRAWING: Figure 9

Description

[Technical field]

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

[0002] A sensorless type motor that does not have a sensor for detecting the rotor position is used as a driving source for an image forming apparatus. When starting the motor, a motor control device that controls a sensorless type motor first detects the stop position of the rotor using a predetermined method. Patent Document 1 discloses a configuration that detects the stop position of the rotor by utilizing a characteristic that the inductance value of the motor coil changes depending on the stop position of the rotor (the rotation phase of the stopped rotor). The motor control device starts driving the motor with forced commutation control based on the detected stop position of the rotor. When the rotation speed of the rotor reaches a predetermined speed or higher, as described in Patent Document 2, the motor control device can detect the rotation position (rotation phase) and rotation speed of the rotor by the induced voltage generated in the coil. Therefore, the motor control device switches the control method from forced commutation control to sensorless control after the rotation speed of the rotor reaches a predetermined speed or higher. [Prior art documents] [Patent documents]

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

[0004] In forced commutation control, the rotation speed of the rotor may overshoot or undershoot the command speed. If forced commutation control is switched to sensorless control in a state in which the command speed is overshooting or undershooting, the coil current flowing through the motor coil may be excessively throttled due to feedback control performed in the sensorless control. If the coil current is excessively throttled, detection of the rotor rotation position and rotation speed in the sensorless control becomes unstable, which may result in unstable motor startup.

[0005] The present invention provides a technique for performing stable motor startup. [Means for solving the problem]

[0006] According to one aspect of the present invention, a motor control device includes a current supplying means for supplying coil current to a plurality of coils of a motor by controlling a voltage applied to the plurality of coils based on a first command value for an excitation current and a second command value for a torque current, a first setting means for setting the first command value, a second setting means for setting the second command value, and A forced commutation is performed by determining the rotation phase of the rotor based on an initial phase when the rotor is stopped and a command value for the rotation speed of the rotor. Using the control, after the rotational speed of the rotor becomes greater than a predetermined speed, A sensorless type rotor control system that determines the rotation phase of the rotor based on the induced voltages of the coils. A control means for switching the control; a determination means for determining a current value of the torque current based on the coil current while the control means is performing the sensorless control; The first setting means comprises: determining a setting value of the first command value greater than 0 based on the current value of the torque current determined by the determination means when the rotor was previously rotated, and switching from the forced commutation control to the sensorless control in a state where the first command value is set to the setting value; The control means Forced commutation Control from the above Sensorless Before switching to the control, the first command value is The set value The present invention is characterized in that: Effect of the Invention

[0007] According to the present invention, a stable motor start can be achieved. [Brief description of the drawings]

[0008] [Figure 1] FIG. 1 is a diagram illustrating the configuration of an image forming apparatus according to an embodiment. [Diagram 2]FIG. 2 is a control configuration diagram of an image forming apparatus according to an embodiment. [Diagram 3] FIG. 2 is a configuration diagram of a motor control unit according to one embodiment. [Figure 4] FIG. 1 is a configuration diagram of a motor according to an embodiment. [Diagram 5] FIG. 2 is a functional block diagram of a microcomputer during forced commutation control according to an embodiment. [Figure 6] FIG. 2 is a functional block diagram of a microcomputer during sensorless control according to an embodiment. [Figure 7] FIG. 10 is an explanatory diagram of a conventional motor start-up process. [Figure 8] FIG. 4 is an explanatory diagram of a motor start-up process according to an embodiment. [Figure 9] 4 is a flowchart of a motor startup process according to one embodiment. [Figure 10] 4 is a flowchart of a motor startup process according to one embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, the embodiments will be described in detail with reference to the attached drawings. Note that the following embodiments do not limit the invention according to the claims. Although the embodiments describe a number of features, not all of these features are essential to the invention, and the features may be combined in any manner. Furthermore, in the attached drawings, the same reference numbers are used for the same or similar configurations, and duplicated descriptions are omitted.

[0010] First Embodiment In the following, the present embodiment will be described using an image forming apparatus as an example of a motor control device. The present invention is not limited to an image forming apparatus, and can be applied to any motor control device that controls a sensorless type motor. FIG. 1 is a configuration diagram of an image forming apparatus according to the present embodiment. The image forming apparatus can be, for example, a printer, a copier, a multifunction machine, a facsimile, or the like. An image forming unit 101 forms a toner image on a photoconductor 102. The image forming unit 101 has a charging unit, an exposure unit, a developing unit, and the like for forming a toner image on the photoconductor 102. The image forming unit 101 transfers the toner image on the photoconductor 102 to a sheet conveyed from a cassette 104 along a conveying path. The sheet is then heated and pressed in a fixing unit 105, and the toner image is fixed. After the toner image is fixed, the sheet is discharged outside the image forming apparatus. A sensorless motor (hereinafter simply referred to as a motor) 103 is a driving source that generates a driving force for driving the photoconductor 102. However, there is no limitation on the load that the motor 103 drives, and the present invention can be applied to the control of the motor 103 that drives any load (member) within the image forming apparatus.

[0011] FIG. 2 shows the control configuration of the image forming apparatus. The printer control unit 107 controls the entire image forming apparatus including the image forming unit 101 and the fixing unit 105 described above. The printer control unit 107 has a processor (not shown) and a memory for storing programs and various control data. The processor of the printer control unit 107 executes programs stored in the memory of the printer control unit 107 to perform various processes for controlling the image forming apparatus. At that time, the printer control unit 107 uses the control data stored in the memory. The communication controller 115 communicates with the host computer 116 and receives image data of an image formed by the image forming apparatus from the host computer 116. The motor control unit 110 controls the motor 103 under the control of the printer control unit 107.

[0012] 3 shows the control configuration of the motor 103. 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 non-volatile 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 to store temporary data. 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).

[0013] 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. 3, 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. For example, a transistor or an FET can be used as the switching elements. 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.

[0014] 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 ON / OFF of each switching element, it is possible to control the coil current flowing through each of the coils 213, 214, and 215. 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 the current detection resistors 219, 220, and 221. The amplifier 218 amplifies the voltage of the current detection resistors 219, 220, and 221 corresponding to the coil current, and outputs it to the 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 coil current of each phase based on the digital value output by the AD converter 203.

[0015] FIG. 4 is a configuration diagram of the motor 103. The motor 103 has a 6-slot stator 501 and a 4-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 made of a permanent magnet. The rotation phase of the rotor 502 is defined based on the rotor 502 being in a predetermined state. As an example, as shown in FIG. 3, the state in which the S pole of the rotor 502 faces the U-phase coil 213 is defined as the reference, that is, the electrical angle is 0, and the electrical angle can be defined as increasing in the counterclockwise direction. In this embodiment, since the number of poles of the rotor 502 is 4, when the rotor rotates counterclockwise by a mechanical angle of π / 2 from the state of FIG. 3, the electrical angle becomes π.

[0016] 5 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 stored in advance in the non-volatile 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 the output torque. The current control unit 302 outputs voltage command values ​​Vd_ref and Vq_ref in a rotating coordinate system based on these values. The coordinate conversion unit 305 performs coordinate conversion from the rotating coordinate system to a stationary coordinate system, and further performs 2-phase-3-phase conversion to generate and output voltage command values ​​Vu, Vv, and Vw of the U-phase, V-phase, and W-phase from the voltage command values ​​Vd_ref and Vq_ref. 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 a PWM signal to be output to the gate driver 210 based on the voltage command values ​​Vu, Vv, and Vw.

[0017] Further, 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 3-phase-2-phase conversion, and further performs coordinate conversion from the stationary coordinate system to a rotating coordinate system to obtain a measurement value Id of the excitation component current and a measurement 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 measurement value Id of the excitation component current and the measurement value Iq of the torque component current to the current control unit 302.

[0018] When the motor 103 is started, the detection unit 301 determines the initial phase of the rotor 502, that is, the electrical angle at the time of stopping (hereinafter, stop angle) θ_std. For example, the configuration described in Patent Document 1 can be applied to detect the electrical angle at the time of stopping the rotor 502. 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 held in the non-volatile 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 at the time of starting.

[0019] 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.

[0020] FIG. 6 is a functional block diagram of the microcomputer 201 in sensorless control. The following mainly describes the points that are different from the functional block diagram in forced commutation control shown in FIG. 5. The estimator 801 estimates the electrical angle θ_est and the rotational speed ω_est of the rotor 502 based on the current values ​​Iu, Iv, and Iw, the 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 forced commutation control. The speed controller 802 calculates a command value Iq_ref for making the rotational speed ω_est 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 the forced commutation control, the speed control unit 802 calculates the command value Iq_ref and outputs it to the current control unit 302, so that the current control unit 302 obtains only the command value Id_ref from the non-volatile memory 205 and uses it.

[0021] As described above, in forced commutation control, the command values ​​Iq_ref and Id_ref both use predetermined values ​​stored in the nonvolatile memory 205. On the other hand, in sensorless control, Id_ref is a predetermined value prepared in advance, but the command value Iq_ref is dynamically set based on the rotation speed ω_est estimated by the estimator 801 and the speed command value ω_ref. Conventionally, in both forced commutation control and sensorless control, the command value Id_ref is set to 0, thereby rotating the motor 103 with high efficiency and high torque.

[0022] FIG. 7 shows the time transition of the rotation speed of the rotor 502 and the effective value of the coil current in the conventional technology. As described above, in the conventional technology, the excitation current command value Id_ref is set to 0 to make the excitation current 0, thereby controlling the motor with high efficiency and high torque. During the forced commutation control, the rotation speed of the rotor 502 may overshoot or undershoot with respect to the speed command value ω_ref depending on the load of the motor 103, etc. In such a state, when the forced commutation control is switched to the sensorless control, the torque current may be throttled depending on the load condition and the overshoot state. When the torque current is throttled and the effective value of the coil current becomes small, the induced voltage cannot be calculated correctly, and the estimation unit 801 becomes unstable in the estimation of the electrical angle θ_est and the rotation speed ω_est of the rotor 502. FIG. 7 shows a case where the motor 103 fails to start as a result of the estimation of the electrical angle θ_est and the rotation speed ω_est becoming unstable.

[0023] For this reason, in this embodiment, in both the forced commutation control and the sensorless control, the command value Id_ref is set to a predetermined value greater than 0. Therefore, even if the torque current is reduced when switching from the forced commutation control to the sensorless control, the command value Id_ref is not 0, so it is possible to prevent the effective value of the coil current from becoming too small due to the excitation current. This allows the estimator 801 to stably estimate the electrical angle θ_est and the rotational speed ω_est, as shown in Fig. 8, and makes it possible to prevent failure in starting the motor 103.

[0024] In this embodiment, the value of the command value Id_ref is set to a predetermined value, but if the value of Id_ref is set too large, torque may be insufficient under high load, and efficiency may deteriorate. For this reason, the value of the command value Id_ref may be determined based on the load of the motor 103. Specifically, the command value Id_ref may be increased as the load of the motor 103 decreases. The magnitude of the load of the motor 103 may be determined based on the measured value Iq of the torque current in the previous sensorless control. In other words, the command value Id_ref may be decreased as the measured value Iq of the torque current in the previous sensorless control increases.

[0025] FIG. 9 is a flow chart of the motor start process according to this embodiment. In S10, the motor control unit 110 sets the command values ​​Iq_ref and Id_ref stored in the non-volatile memory 205. In this embodiment, both the command values ​​Iq_ref and Id_ref are greater than 0. In S11, the motor control unit 110 starts the rotation of the motor 103 by forced commutation control. In S12, the motor control unit 110 continues the forced commutation control until the speed command value ω_ref from the printer control unit 107 becomes equal to or greater than a threshold value that is a predetermined speed. After the speed command value ω_ref becomes equal to or greater than the threshold value, the motor control unit 110 switches from the forced commutation control to the sensorless control in S13. The threshold value is equal to or greater than the rotation speed of the rotor 502 at which the estimator 801 can estimate the electrical angle θ_est and the rotation speed ω_est based on the induced voltage of the coil.

[0026] Second Embodiment Next, the second embodiment will be described focusing on the differences from the first embodiment. In the first embodiment, the motor control unit 110 sets the command value Id_ref to a value greater than 0 before the start of startup of the motor 103. In this embodiment, with an emphasis on efficiency, the command value Id_ref is set to 0 before the start of startup of the motor 103. Then, when switching to sensorless control, the command value Id_ref is set to a value greater than 0 immediately before the switching.

[0027] FIG. 10 is a flow chart of the motor start-up process according to this embodiment. In S20, the motor control unit 110 sets command values ​​Iq_ref and Id_ref. In this embodiment, the command value Iq_ref set in S20 is a value greater than 0, but the command value Id_ref set in S20 is 0. In S21, the motor control unit 110 starts the rotation of the motor 103 by forced commutation control. In S22, the motor control unit 110 continues the forced commutation control until the speed command value ω_ref from the printer control unit 107 becomes equal to or greater than a threshold value. After the speed command value ω_ref becomes equal to or greater than the threshold value, in S23, the motor control unit 110 changes the command value Id_ref to a value greater than 0. Thereafter, in S24, the motor control unit 110 switches from the forced commutation control to the sensorless control.

[0028] <Other> In the first embodiment, the command value Id_ref is set to a value greater than 0 before the start of the forced commutation control, and in the second embodiment, the command value Id_ref is set to 0 before the start of the forced commutation control, and the command value Id_ref is set to a value greater than 0 immediately before switching to the sensorless control. However, the command value Id_ref may be set to a value greater than 0 at any timing before switching to the sensorless control after the command value Id_ref is set to 0 and the forced commutation control is started. Note that the motor control unit 110 maintains the command value Id_ref at a value greater than 0 until at least a predetermined period has elapsed after setting the command value Id_ref to a value greater than 0 and switching to the sensorless control. After the predetermined period has elapsed, the command value Id_ref may be changed to 0. Alternatively, the command value Id_ref may be maintained at a value greater than 0 even after the predetermined period has elapsed. The predetermined period is determined in advance based on the period during which the influence of the overshoot and undershoot during the forced commutation control continues after switching to the sensorless control. In addition, in S12 in FIG. 9 and S22 in FIG. 10, it is determined whether or not the speed command value ω_ref is equal to or greater than the threshold value. However, it may be determined whether or not the speed command value ω_ref is greater than the threshold value.

[0029] In the above embodiments, the motor control unit 110 is one component of the image forming apparatus, so it is referred to as the motor control unit 110. However, the motor control unit 110 can be a single device and be a motor control device. Also, a device including the printer control unit 107 and the motor control unit 110 can be a motor control device. In the above embodiments, the motor 103 rotates the photoconductor 102, but the present invention can be applied to a motor that drives any rotating member in the image forming apparatus. Also, the configuration of the motor 103 is not limited to the configuration shown in FIG. 4, and it may be a motor with a different number of poles or phases.

[0030] [Other embodiments] The present invention can also be realized by a process in which a program for implementing one or more of the functions of the above-described embodiments is supplied to a system or device via a network or a storage medium, and one or more processors in a 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 implements one or more of the functions.

[0031] The invention is not limited to the above-described embodiments, and various modifications and variations are possible 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]

[0032] 211: inverter, 205: non-volatile memory, 802: speed control section, 201: microcomputer

Claims

1. a current supplying means for supplying coil currents to the plurality of coils of the motor by controlling a voltage applied to the plurality of coils based on a first command value of an excitation current and a second command value of a torque current; a first setting means for setting the first command value; A second setting means for setting the second command value; a control means for using forced commutation control when starting rotation of a rotor of the motor by determining a rotation phase of the rotor based on an initial phase when the rotor is stopped and a command value for a rotation speed of the rotor, and switching to sensorless control by determining the rotation phase of the rotor based on induced voltages of the plurality of coils after the rotation speed of the rotor becomes higher than a predetermined speed; a determination means for determining a current value of the torque current based on the coil current while the control means is performing the sensorless control; Equipped with the first setting means determines a set value of the first command value greater than 0 based on the current value of the torque current determined by the determination means when the rotor was previously rotated, and sets the set value as the first command value before the control means switches from the forced commutation control to the sensorless control such that the forced commutation control can be switched to the sensorless control with the first command value set to the set value.

2. 2. The motor control device according to claim 1, wherein the first setting means sets the set value as the first command value before the control means starts the forced commutation control.

3. 2. The motor control device according to claim 1, wherein the first setting means sets the first command value to 0 before the control means starts the forced commutation control, and sets the setting value as the first command value before the control means switches from the forced commutation control to the sensorless control.

4. the first setting means sets the first command value to 0 before the control means starts the forced commutation control, and sets the first command value to the set value when the rotational speed of the rotor becomes higher than the predetermined speed; 4. The motor control device according to claim 3, wherein the control means switches from the forced commutation control to the sensorless control after the set value is set as the first command value.

5. 5. The motor control device according to claim 1 , wherein the first setting means maintains the first command value at a value greater than 0 until at least a predetermined period of time has elapsed since the control means switches from the forced commutation control to the sensorless control.

6. 6. The motor control device according to claim 1, wherein the second setting means sets a value greater than 0 as the second command value while the control means is performing the forced commutation control.

7. 7. The motor control device according to claim 1, wherein the first setting means reduces the set value as the current value of the torque component current increases.

8. a rotating member for transporting the sheet along a transport path; an image forming unit for forming an image on the sheet conveyed along the conveying path; a motor for driving the rotating member or the image forming means; A motor control means for controlling the motor; An image forming apparatus comprising: The motor control means a current supplying means for supplying coil currents to the plurality of coils of the motor by controlling a voltage applied to the plurality of coils based on a first command value of an excitation current and a second command value of a torque current; a first setting means for setting the first command value; A second setting means for setting the second command value; a control means for using forced commutation control when starting rotation of a rotor of the motor by determining a rotation phase of the rotor based on an initial phase when the rotor is stopped and a command value for a rotation speed of the rotor, and switching to sensorless control by determining the rotation phase of the rotor based on induced voltages of the plurality of coils after the rotation speed of the rotor becomes higher than a predetermined speed; a determination means for determining a current value of the torque current based on the coil current while the control means is performing the sensorless control; Equipped with the first setting means determines a setting value of the first command value greater than 0 based on the current value of the torque current determined by the determination means when the rotor was previously rotated, and sets the setting value as the first command value before the control means switches from the forced commutation control to the sensorless control so that the forced commutation control can be switched to the sensorless control with the first command value set to the setting value.

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