Patent Publication Number: US-11664751-B2

Title: Motor control apparatus and image forming apparatus that detect rotor position

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a Continuation of U.S. patent application Ser. No. 16/781,101, filed on Feb. 4, 2020, which claims priority to Japanese Patent Application No. 2019-027653, filed Feb. 19, 2019, the entire contents of which are both hereby incorporated by reference herein. 
    
    
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to a motor control technique, and more particularly, to a technique for suppressing fluctuations in the output voltage of a power supply in a detection processing of the rotor position in a motor. 
     Description of the Related Art 
     A sensorless DC brushless motor having no Hall element is used as a driving source for a rotating member of an image forming apparatus. For the sensorless DC brushless motor, the rotor position can be detected using an induced voltage during high-speed rotation of the rotor. However, during stoppage of the rotor or during low-speed rotation with a low induced voltage, the rotor position cannot be detected using the induced voltage. For this reason, US-2015-145454 discloses a configuration in which the rotor position is detected by measuring the coil impedance, which changes depending on the rotor position. In US-2015-145454, the coil impedance is measured by passing a current through the coil. 
     Here, a switching power supply that supplies operating power to the motor performs feedback control in order to make the output DC voltage constant. However, in the configuration described in US-2015-145454, since the amount of change per unit time in the current flowing through the coil is large, it cannot be followed by feedback control, causing a voltage drop or ripples in the output voltage of the switching power supply. Although the voltage drop and the ripples can be reduced by increasing the capacity of a smoothing capacitor of the switching power supply, the substrate area is increased, leading to an increase in costs. 
     Japanese Patent Laid-Open No. 2014-147259 discloses a configuration in which the on-time of a switching element of the switching power supply is increased in order to suppress fluctuations in the output voltage of the switching power supply due to a load change. 
     However, if the on-time of the switching element of the switching power supply is increased irrespective of a small load, power is excessive until the load increases, resulting in that the output voltage becomes temporarily higher than that in the steady state. In the rotor position detection processing described in US-2015-145454, a value of the current flowing through the coil, that is, the load changes depending on the rotor position. Therefore, it is difficult to adjust the timing at which the switching element is turned on in advance, and it is difficult to apply the technique described in Japanese Patent Laid-Open No. 2014-147259 in order to reduce ripples. 
     SUMMARY OF THE INVENTION 
     According to an aspect of the present invention, a motor control apparatus includes: a switching power supply; a first motor configured to operate with a voltage from the switching power supply; and a control unit configured to control the first motor, wherein the control unit is further configured to cause the switching power supply to supply power of the switching power supply to a load other than the first motor before detecting an initial position of a rotor of the first motor using a current flowing through the first motor. 
     Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a configuration diagram of an image forming apparatus according to an embodiment; 
         FIG.  2    is a configuration diagram of a switching power supply unit according to an embodiment. 
         FIG.  3    is a diagram illustrating an output characteristic of the switching power supply unit according to an embodiment. 
         FIG.  4    is a configuration diagram of a motor control unit according to an embodiment. 
         FIGS.  5 A and  5 B  are configuration diagrams of a motor according to an embodiment. 
         FIG.  6    is a graph illustrating a relationship between an excitation phase and a combined inductance according to an embodiment. 
         FIG.  7 A  is a waveform chart illustrating an excitation current in rotor position detection processing. 
         FIG.  7 B  is a waveform chart illustrating an output voltage of the switching power supply unit in the rotor position detection processing. 
         FIGS.  8 A and  8 B  are sequence diagrams of the rotor position detection processing according to an embodiment. 
         FIGS.  9 A and  9 B  are operation explanatory diagrams of the switching power supply unit in the rotor position detection processing according to an embodiment. 
         FIG.  10    is a configuration diagram of a switching power supply unit according to an embodiment. 
         FIGS.  11 A to  11 C  are operation explanatory diagrams of the switching power supply unit in the rotor position detection process according to an embodiment. 
         FIGS.  12 A to  12 D  are diagrams illustrating a driving signal in the rotor position detection processing according to an embodiment. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     Hereinafter, embodiments will be described in detail with reference to the attached drawings. Note, the following embodiments are not intended to limit the scope of the claimed invention. Multiple features are described in the embodiments, but limitation is not made an invention that requires all such features, and multiple such features may be combined as appropriate. Furthermore, in the attached drawings, the same reference numerals are given to the same or similar configurations, and redundant description thereof is omitted. 
     First Embodiment 
       FIG.  1    is a configuration diagram of an image forming apparatus  1  according to the present embodiment, such as a printer, a copier, a multifunction device, and a facsimile. The image forming apparatus  1  forms a full color image by superimposing four color toner images of yellow (Y), magenta (M), cyan (C), and black (K). In  FIG.  1   , Y, M, C, and K at ends of reference numerals indicate that the colors of the toner images involved in the formation of members indicated by the reference numerals are yellow, magenta, cyan, and black. In the following description, when it is not necessary to distinguish the colors from each other, reference numerals excluding Y, M, C, and K at the ends are used. At image formation, a photosensitive member  11  is rotationally driven in a clockwise direction in the drawing. A charging unit  12  charges the surface of the photosensitive member  11  to a uniform potential. An exposing unit  13  exposes the surface of the photosensitive member  11  with light to form an electrostatic latent image on the photosensitive member  11 . A developing roller  15  of a developing unit develops the electrostatic latent image on the photosensitive member  11  with toner and visualizes the image as a toner image. A primary transfer unit  16  transfers the toner image formed onto the photosensitive member  11  to an intermediate transfer belt  17  by primary transfer bias. The toner image formed on each photosensitive member  11  is superimposed and transferred onto the intermediate transfer belt  17  to form a full-color image on the intermediate transfer belt  17 . The intermediate transfer belt  17  is rotationally driven in the counterclockwise direction in the figure by a driving roller  20 . As a result, the toner image transferred onto the intermediate transfer belt  17  is conveyed to a position opposed to a secondary transfer unit  19 . 
     On the other hand, a recording material (sheet) P stored in a cassette  2  is fed to a conveyance path  26  by a feeding roller  4 , and is conveyed to the position opposed to the secondary transfer unit  19  by a conveying roller  5 . The secondary transfer unit  19  transfers the toner image on the intermediate transfer belt  17  onto the recording material P by secondary transfer bias. Thereafter, the recording material P is conveyed to a fixing device  22 . The fixing device  22  heats and presses the recording material P to fix the toner image on the recording material P. The recording material P on which the toner image is fixed is discharged to the outside of the image forming apparatus  1  by a discharge roller  23 . A stepping motor  7  transmits a driving force to the feeding roller  4  and the conveying roller  5  through a gear mechanism not illustrated. Further, the DC brushless motor  6  is controlled by a motor control unit  41  such that its driving force is transmitted to the photosensitive member  11 , the charging unit  12 , the developing roller  15 , the primary transfer unit  16 , and the driving roller  20  through a gear mechanism not illustrated. It is noted that the DC brushless motor  6  is a sensorless-type motor that includes no Hall element and requires initial position detection processing at activation. On the contrary, the stepping motor  7  is a motor that does not require the initial position detection processing at activation. The stepping motor  7  and the DC brushless motor  6  operate with power from a switching power supply unit  100 . The switching power supply unit  100  operates with AC power supplied from an external power supply  40  such as a commercial power supply. A control unit  3  controls the entire image forming apparatus  1 . 
       FIG.  2    is a configuration diagram of the switching power supply unit  100 . Note that the switching power supply unit  100  in the present embodiment is a current resonance type. The AC voltage supplied from the external power supply  40  is applied to a rectifier diode bridge  104  via an input filter  103 . The rectifier diode bridge  104  rectifies the AC voltage and outputs a DC voltage. A primary smoothing capacitor  105  is connected to the rectifier diode bridge  104  in parallel. A DC voltage output from the rectifier diode bridge  104  is applied to a primary winding  109  of a transformer  108  via a switching FET  106 . A current resonance capacitor  111  is connected to the primary winding  109  in series. A switching FET  107  is connected to the primary winding  109  in parallel. The transformer  108  includes an auxiliary winding  301  in addition to secondary windings  201  and  202 . 
     A power supply control IC  110  includes a VH terminal, a VSEN terminal, a VGH terminal and a VGL terminal that output driving signals for driving the switching FETs  106  and  107 , a Vcc terminal that is a power supply terminal, and an FB terminal for feeding back an output voltage Vo. A voltage smoothed by the primary smoothing capacitor  105  is input to the VH terminal of the power supply control IC  110 , and a voltage acquired by dividing the smoothed voltage by resistors  120  and  121  is input to the VSEN terminal. First, using the voltage input to the VH terminal, the power supply control IC  110  increases the voltage at the Vcc terminal to an activation start voltage. When the voltage input to the VSEN terminal increases to an operation start voltage, the power supply control IC  110  outputs driving signals from the VGH terminal and the VGL terminal, and starts switching control of the switching FETs  106  and  107 . Thereby, when the transformer  108  is driven, power is supplied from the auxiliary winding  301  to the Vcc terminal of the power supply control IC  110 . When power supply from the auxiliary winding  301  to the Vcc terminal is started, the power supply control IC  110  cuts off power supply from the VH terminal to the Vcc terminal. In  FIG.  2   , a dashed line indicates a current during turn-on of the switching FET  106 , and a dotted line indicates a current during turn-on of the switching FET  107 . 
     Further, when the power supply control IC  110  starts switching control of the switching FETs  106  and  107 , an induced voltage is generated in each of the secondary windings  201  and  202  of the transformer  108 . This induced voltage is smoothed by a rectifying/smoothing circuit  203  including a rectifying diode and a smoothing capacitor, and is supplied to a load  204  as a DC output voltage Vo. In the present embodiment, the load  204  includes the DC brushless motor  6  and the stepping motor  7 . A voltage acquired by dividing the output voltage Vo by resistors  402  and  403  is input to a shunt regulator  404 . The shunt regulator  404  turns on/off of a photocoupler  405  according to the input voltage. The power supply control IC  110  includes a constant current circuit therein and outputs a constant current from the FB terminal. Charges of this constant current are stored in a capacitor  401 . Accordingly, the voltage at the FB terminal changes depending on the on/off of the photocoupler  405 . The power supply control IC  110  controls the output voltage Vo to be constant by controlling the switching frequency of the switching FETs  106  and  107  according to the voltage of the FB terminal. 
     In the current resonance-type switching power supply unit  100 , the switching frequency changes according to the load  204 .  FIG.  3    illustrates an output characteristic of the switching power supply unit  100 . As illustrated in  FIG.  3   , the output characteristic draws a curve having a maximum value at a resonance frequency f 0  due to an excitation inductance Lp and a leakage inductance Ls of the transformer  108  and a capacitance Ci of the current resonance capacitor  111 . As the load is smaller, the frequency increases, and as the load is larger, the frequency decreases. 
       FIG.  4    is a configuration diagram of the motor control unit  41  that controls the DC brushless motor  6 . The motor control unit  41  includes a processing unit  51  embodied as, for example, a microcomputer. A communication port  52  performs serial data communication with the control unit  3 . A pulse width modulation (PWM) port  58  outputs a PWM signal for driving each switching element of a three-phase inverter  60 . The three-phase inverter  60  has a total of six switching elements on a high (H) side and a low (L) side for each of three phases (U, V, W) of the DC brushless motor  6 . The switching element each are an FET, for example, and driven with an individual PWM signal. Therefore, the PWM port  58  has a total of six terminals of U-H, V-H, W-H, U-L, V-L, and W-L corresponding to the six switching elements. A DC voltage is applied from the switching power supply unit  100  to the three-phase inverter  60 . The PWM signal turns on/off each of the switching elements of the three-phase inverter  60 , passing the excitation current through a plurality of coils  73  (U phase),  74  (V phase) and  75  (W phase) of the DC brushless motor  6 . In this way, the three-phase inverter  60  operates as an exciting unit for exciting the DC brushless motor  6 . The excitation current flowing through each of the coils  73 ,  74 , and  75  each is converted into a voltage by the resistor  63 , and is input to an AD converter  53  of the processing unit  51  as a value indicating the excitation current. The nonvolatile memory  55  is a holding unit for holding data used by the processing unit  51  for processing. 
     Next, the structure of the DC brushless motor  6  will be described with reference to  FIGS.  5 A and  5 B . In this embodiment, the DC brushless motor  6  has a six-slot stator  71  and a four-pole rotor  72 , and the stator  71  is provided with the three-phase (U, V, W) coils  73 ,  74 ,  75 . The rotor  72  is composed of a permanent magnet and has two north poles and two south poles. The position of the rotor  72  (rotation phase at stoppage or low-speed rotation) is determined by the combination of the excited coils  73 ,  74 ,  75 , that is, the excitation phase. In the following description, exciting the X-Y phase excitation means exciting the X-Y phase such that the X phase becomes the N pole and the Y phase becomes the S pole. For example, when the U-V phase is excited, the U phase (coil  73 ) becomes the N pole and the V phase (coil  74 ) becomes the S pole, and the rotor  72  stops at the position illustrated in  FIG.  5 A . Next, when the U-W phase is excited, the U phase (coil  73 ) becomes the N pole and the W phase (coil  75 ) becomes the S pole, and the rotor  72  stops at the position illustrated in  FIG.  5 B . 
     Subsequently, detection of the rotational position (rotational phase) of the rotor  72  during the stoppage of the DC brushless motor  6  will be described. In the present embodiment, the position of the rotor  72  is detected by utilizing the fact that the inductance of each of the coils  73 ,  74 , and  75  changes depending on the position of the rotor  72 . Generally, the coil is configured to wind a copper around a core formed of laminated electromagnetic steel sheets. Further, when an external magnetic field is present, the magnetic permeability of the magnetic steel sheet is low, and the coil inductance proportional to the magnetic permeability is also small. For example, as illustrated in  FIG.  5 A , it is assumed that the rotor  72  is stopped such that the U-phase coils  73  are opposed to only the south pole of the rotor  72 . In this case, since the influence of the external magnetic field by the rotor  72  is large, the decreasing rate of the inductance of the coil  73  increases. The decreasing rate of the inductance also changes depending on the direction of the current flowing through the U-phase coil  73 . Specifically, the decreasing rate of the inductance becomes larger when the direction of the magnetic field generated by the current flowing through the coil  73  is the same as the direction of the external magnetic field from the rotor  72  than when the direction is reversed. Therefore, in the case of  FIG.  5 A , comparing the case where the U phase (coil  73 ) is excited to the N pole and with the case where the case where the U phase (coil  73 ) is excited to the S pole, the decreasing rate of the inductance is greater when the U phase (coil  73 ) is excited to the N pole. On the other hand, in the state of  FIG.  5 A , the W phase (coil  75 ) is opposed to both the S pole and the N pole of the rotor  72 . Therefore, the coil  75  is less affected by the external magnetic field from the rotor  72  than the coil  73  and thus, the decreasing rate of the inductance of the coil  75  is smaller than that of the coil  73 . In this manner, the inductances of the coils  73 ,  74 , and  75  vary depending on the position of the rotor  72 . 
       FIG.  6    illustrates the combined inductance measured by applying an excitation current to each excitation phase in the case where the rotor  72  is stopped at the position where the U-V phase is excited. In the following description, the position of the rotor  72  is indicated by its excitation phase. For example, the rotational position of the rotor  72  illustrated in  FIG.  5 A  when the U-V phase is excited is referred to as the U-V phase position. As illustrated in  FIG.  6   , since the rotor  72  is stopped at the U-V phase position, the combined inductance measured when the U-V phase is excited is smaller than the combined inductance measured when the other excitation phases are excited. As described above, in this embodiment, all the excitation phases are sequentially excited to measure their combined inductances, and in accordance with a determination of the magnitude relationship of the combined inductances, the rotational position of the rotor  72  is determined. In the following description, excitation for determining the rotational position of the rotor  72  is referred to as position determination excitation. 
     In the present embodiment, the position determination excitation of each excitation phase is divided into an A period (first period) and a B period following the A period. For example, when the U-V phase is excited, during the period A (first period), a PWM signal having a predetermined duty, for example, 80% duty is output from the U-H terminal. In the period A, it is assumed that the V-L terminal is at a high level (duty is 100%), and the other terminals are at a low level (duty is 0%). In the B period (second period) following the A period, a PWM signal having a predetermined duty, for example, 80% duty is output from the V-H terminal. In the period B, it is assumed that the U-L terminal is at a high level (duty is 100%), and the other terminals are at a low level (duty is 0%). The excitation current flowing from the U-phase coil  73  toward the V-phase coil  74  increases in the A period, and decreases in the B period. The time lengths of the A period and the B period are determined based on necessary detection accuracy, with an upper limit being the period during which the rotor  72  does not rotate. In this example, each time length is set to 0.5 ms. 
       FIG.  7 A  illustrates a change over time in the excitation current flowing when excitation phases are sequentially subjected to the position determination excitation. The excitation current is detected by the resistor  63  and the AD converter  53  in  FIG.  4   . In the period in which the duty of the PWM signal is constant, the coil inductance changes depending on the magnitude of the excitation current and thus, the excitation current increases or decreases curvilinearly rather than linearly. The processing unit  51  detects a peak value of the excitation current at the position determination excitation of each excitation phase, thereby determining the relative magnitude of the combined inductance of each excitation phase to detect the position of the rotor  72 . Specifically, since the peak value of the excitation current increases as the combined inductance decreases, the processing unit  51  determines that the position of the rotor  72  is the excitation phase position where the peak value of the excitation current is maximum. 
     When a current as illustrated in  FIG.  7 A  is passed from the switching power supply unit  100  operating in a state where the load  204  is small, that is, the output current is small, ripples as illustrated in  FIG.  7 B  are generated in the output voltage Vo of the switching power supply unit  100 . In order to reduce the ripples, it is necessary to increase the capacitance of the capacitor included in the switching power supply unit  100 , or to reduce the impedance by thickening a wiring between the DC brushless motor  6  and the switching power supply unit  100 . However, this makes the motor control unit  41  and the switching power supply unit  100  larger. 
     Therefore, in this embodiment, prior to the position determination excitation of the rotor  72  of the DC brushless motor  6 , the stepping motor  7  is put into the hold excitation state, thereby reducing the ripples in the switching power supply unit  100 . Specifically, as illustrated in  FIG.  8 A , when receiving a print job, the control unit  3  first performs hold excitation of the stepping motor  7 . When a predetermined period Td has elapsed since the hold excitation of the stepping motor  7 , the control unit  3  starts the position determination excitation and detects an initial position of the rotor  72  of the DC brushless motor  6 . When detecting the initial position of the rotor  72 , the control unit  3  controls the motor control unit  41  to activate the DC brushless motor  6  and transitions the DC brushless motor  6  to a steady operation of rotating at a target rotational speed. The period Td is a period elapsed until the change in the switching frequency of the switching power supply unit  100  due to the hold excitation of the stepping motor  7  is settled, that is, a period elapsed until the fluctuations in the output voltage of the switching power supply unit  100  is settled, or a longer period. As illustrated in  FIG.  8 B , the hold excitation of the stepping motor  7  may be canceled at start of the position determination excitation. That is, the control unit  3  continues the hold excitation of the stepping motor  7  at least until the processing of detecting the initial position of the rotor  72  of the DC brushless motor  6  is started. 
     Hereinafter, the reason why the ripples in the switching power supply unit  100  can be reduced by the control as illustrated in  FIGS.  8 A and  8 B  will be described.  FIG.  9 A  illustrates the same output characteristic of the same switching power supply unit  100  as that in  FIG.  3   . A frequency f 1  in  FIG.  9 A  is a switching frequency before the hold excitation of the stepping motor  7 , and the image forming apparatus  1  is in a light-load state before a printing operation. A frequency f 1 ′ is a switching frequency during the hold excitation of the stepping motor  7 . A frequency f 2  is a switching frequency at the position detection processing of the rotor  72  of the DC brushless motor  6 , and a frequency f 2 ′ is a switching frequency in the case where the position detection processing of the rotor  72  of the DC brushless motor  6  is performed during the hold excitation of the stepping motor  7 . 
     When the position determination excitation of the rotor  72  of the DC brushless motor  6  is performed without performing the hold excitation of the stepping motor  7 , the switching frequency of the switching power supply unit  100  changes from f 1  to f 2  in  FIG.  9 A  by a frequency T 1 . While the switching frequency changes, ripples occurs in the output voltage Vo of the switching power supply unit  100 . In the present embodiment, since the position determination excitation of the rotor  72  of the DC brushless motor  6  is started during the hold excitation of the stepping motor  7 , the switching frequency of the switching power supply unit  100  changes from f 1 ′ to f 2 ′ in  FIG.  9 A  by a frequency T 2 . As illustrated in  FIG.  9 A , since the change in the output power with respect to the change in frequency is larger toward a maximum value (frequency f 0 ) of the output characteristic, T 2  is smaller than T 1 . That is, by performing the hold excitation of the stepping motor  7  prior to the position determination excitation, the change in the switching frequency can be reduced and thus, the ripples of the output voltage of the switching power supply unit  100  can be suppressed. 
     As illustrated in  FIG.  8 B , the hold excitation of the stepping motor  7  may be canceled at start of the position determination excitation. By canceling hold excitation of the stepping motor  7  at start of position determination excitation, the switching frequency of the switching power supply unit  100  changes from f 1 ′ to f 2  in  FIG.  9 B  by a frequency T 3 . However, the change T 3  is smaller than T 2 . Therefore, the ripples of the output voltage of the switching power supply unit  100  can be further suppressed. 
     As described above, the position determination excitation of the rotor  72  of the DC brushless motor  6  is started after the hold excitation of the stepping motor  7 . With this configuration, the change in the switching frequency of the switching power supply unit  100  can be reduced, thereby reducing the ripples of the output voltage Vo. Further, in the configuration of the present embodiment, the hold excitation of the stepping motor  7  is merely performed prior to the start of the position determination excitation of the rotor  72  of the DC brushless motor  6 , which can be executed without any restrictions on the sequence in image formation. Note that the stepping motor  7  may be rotationally controlled instead of performing the hold excitation of the stepping motor  7 . 
     In the present embodiment, in order to reduce the change in the switching frequency at start of position determination excitation of the rotor  72  of the DC brushless motor  6 , power is supplied to the stepping motor  7  in advance. However, in order to reduce the change in the switching frequency at start of position determination excitation, a predetermined amount of power or more may be supplied to another load in the image forming apparatus  1  in advance. 
     Second Embodiment 
     The following describes a second embodiment mainly about differences from the first embodiment. In the first embodiment, the switching power supply unit  100  is a current resonance type. In the present embodiment, the flyback type switching power supply unit  100  is used. 
       FIG.  10    is a configuration diagram of the switching power supply unit  100  in the present embodiment. Similar components to the components of the switching power supply unit  100  ( FIG.  2   ) in the first embodiment are given the same referential numerals, and detailed description thereof is omitted. Hereinafter, the configuration of the switching power supply unit  100  of the present embodiment will be described focusing on differences from the switching power supply unit  100  of the first embodiment. A power supply control IC  110  has a VH terminal, a CS terminal, an OUT terminal that outputs a driving signal for driving a switching FET  106 , a Vcc terminal that is a power supply terminal, and an FB terminal for feeding back an output voltage Vo. An inter-terminal voltage of a current detection resistor  112  for converting a current flowing through a primary winding  109  and the switching FET  106  into a voltage is input to the CS terminal. The power supply control IC  110  charges a capacitor  307  connected to the Vcc terminal with a voltage, which is smoothed by a primary smoothing capacitor  105  and input to the VH terminal. When the voltage at the Vcc terminal rises to an activation start voltage, the power supply control IC  110  outputs the driving signal from the OUT terminal. As a result, power is supplied from an auxiliary winding  301  to the Vcc terminal, and power supply from the VH terminal to the Vcc terminal is cut off. The driving signal output from the OUT terminal is determined by the voltage input to the CS terminal and a voltage input to the FB terminal (hereinafter referred to as FB voltage). Specifically, the power supply control IC  110  outputs a low level while the voltages while the CS terminal and the FB terminal are equal, and outputs a high level during other periods. Therefore, the output voltage Vo can be controlled by controlling the voltage at the FB terminal. 
     The power supply control IC  110  in the present embodiment changes the switching frequency for switching the switching FET  106  according to the FB voltage.  FIG.  11 A  illustrates a switching frequency characteristic of the switching power supply unit  100  according to the present embodiment. The FB voltage becomes higher as the load of the load  204  becomes larger. In the section where the FB voltage is between Vfb 1  and Vfb 2 , a discontinuous operation is performed at the lowest switching frequency. A continuous operation is performed when the FB voltage is Vfb 2  or more, and the switching frequency increases to a maximum frequency fmax as the load  204  increases. 
     Also in the present embodiment, as in the first embodiment, the hold excitation of the stepping motor  7  is performed prior to the start of the position determination excitation of the DC brushless motor  6 . Vfba 1  in  FIG.  11 B  is the FB voltage before the hold excitation of the stepping motor  7 , and the image forming apparatus  1  is in a light-load state before a printing operation. At this time, the power supply control IC  110  is in a discontinuous mode of discontinuously performing the switching operation, in which a discontinuous driving signal as illustrated in  FIG.  12 A  is output from the OUT terminal. A voltage Vfba 1 ′ is an FB voltage during the hold excitation of the stepping motor  7 . At this time, the power supply control IC  110  is in a continuous mode of continuously performing the switching operation, in which a driving signal as illustrated in  FIG.  12 B  is output from the OUT terminal. The voltage Vfba 2  is an FB voltage at the position determination excitation of the rotor  72  of the DC brushless motor  6 . At this time, the power supply control IC  110  is in a continuous mode, in which a driving signal as illustrated in  FIG.  12 C , having a higher frequency than the driving signal in  FIG.  12 B  is output from the OUT terminal. A voltage Vfba 2 ′ is an FB voltage at the hold excitation of the stepping motor  7  and the position determination excitation of the rotor  72  of the DC brushless motor  6 . At this time, the power supply control IC  110  is in a continuous mode, in which a driving signal as illustrated in  FIG.  12 D , having a higher frequency than the driving signal in  FIG.  12 C  is output from the OUT terminal. 
     When the position determination excitation of the rotor  72  of the DC brushless motor  6  is performed without performing the hold excitation of the stepping motor  7 , the FB voltage of the switching power supply unit  100  changes from Vfba 1  to Vfba 2  in  FIG.  11 B . At this time, the power supply control IC  110  must transition from the discontinuous mode to the continuous mode, generating voltage ripples of the output voltage Vo due to the mode transition and the change in the switching frequency. In the present embodiment, since the position determination excitation of the rotor  72  of the DC brushless motor  6  is started during the hold excitation of the stepping motor  7 , the FB voltage transitions from Vfba′ 1  to Vfba′ 2  in  FIG.  11 B . At this time, the power supply control IC  110  remains in the continuous mode and no mode transition occurs. That is, the mode transition may be prevented by performing the hold excitation of the stepping motor  7 , thereby suppressing ripples of the output voltage of the switching power supply unit  100 . 
     As illustrated in  FIG.  11 C , the hold excitation of the stepping motor  7  may be canceled at the start of position determination excitation. By canceling the hold excitation of the stepping motor  7  at the start of the position determination excitation, the change in the switching frequency of the switching power supply unit  100  can be further reduced to further suppress the ripples of the output voltage of the switching power supply unit  100 . 
     As described above, the position determination excitation of the rotor  72  of the DC brushless motor  6  is preformed after the hold excitation of the stepping motor  7 . The ripples of the output voltage Vo can be reduced by transitioning the operation mode of the power supply control IC  110  to the continuous mode in advance through the hold excitation of the stepping motor  7 . Further, in the configuration of the present embodiment, the hold excitation of the stepping motor  7  is merely performed prior to the start of the position determination excitation of the rotor  72  of the DC brushless motor  6 , which can be executed without any restrictions on the sequence in image formation. Note that the stepping motor  7  may be rotationally controlled instead of performing the hold excitation of the stepping motor  7 . Furthermore, before performing the position determination excitation, a predetermined amount of power or more for transitioning the operation mode of the switching power supply unit  100  to the continuous mode may be supplied to a load in the image forming apparatus other than the stepping motor  7 . 
     In each of the above-described embodiments, the motor control unit  41  is described as a component of the image forming apparatus  1 . However, the motor control unit  41  may be a single device that serves as a motor control apparatus. Further, an apparatus including the control unit  3  and the motor control unit  41  may be a motor control apparatus. In the above embodiments, the DC brushless motor  6  supplies a driving force to the image forming unit such as the photosensitive member  11  of the image forming apparatus  1 . However, the DC brushless motor  6  may supply a driving force to a conveying unit for conveying the recording material P. Further, the configuration of the DC brushless motor  6  is not limited to the configuration illustrated in  FIGS.  5 A and  5 B , and may be a motor having another number of poles or phases. 
     Other Embodiments 
     Embodiments of the present invention can also be realized by a computer of a system or apparatus that reads out and executes computer executable instructions (e.g., one or more programs) recorded on a storage medium (which may also be referred to more fully as a ‘non-transitory computer-readable storage medium’) to perform the functions of one or more of the above-described embodiments and/or that includes one or more circuits (e.g., application specific integrated circuit (ASIC)) for performing the functions of one or more of the above-described embodiments, and by a method performed by the computer of the system or apparatus by, for example, reading out and executing the computer executable instructions from the storage medium to perform the functions of one or more of the above-described embodiments and/or controlling the one or more circuits to perform the functions of one or more of the above-described embodiments. The computer may comprise one or more processors (e.g., central processing unit (CPU), micro processing unit (MPU)) and may include a network of separate computers or separate processors to read out and execute the computer executable instructions. The computer executable instructions may be provided to the computer, for example, from a network or the storage medium. The storage medium may include, for example, one or more of a hard disk, a random-access memory (RAM), a read only memory (ROM), a storage of distributed computing systems, an optical disk (such as a compact disc (CD), digital versatile disc (DVD), or Blu-ray Disc (BD)™), a flash memory device, a memory card, and the like. 
     While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions. 
     This application claims the benefit of Japanese Patent Application No. 2019-027653, filed on Feb. 19, 2019, which is hereby incorporated by reference herein in its entirety.