Motor control device and image forming apparatus

Abstract

To provide a technique to shorten the time required for determination of a stop position of a rotor of a motor to be controlled.SOLUTION: When a processing unit 51 excites a plurality of excitation phases of a motor 150, in a first period, drives, with a first PWM signal, a first switching element connected with a first phase coil in the excitation phase to be excited, and in a second period after the first period, drives, with a second PWM signal, a second switching element connected with a second phase coil in the excitation phase. In that case, the processing unit 51 controls the duty ratio of the second PWM signal to be output to the second switching element in the second period based on a supply voltage supplied by a low-voltage power source 120. The processing unit 51 determines a stop position of a rotor of the motor 150 based on a result of measurement of excitation current obtained by exciting the plurality of excitation phases.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a motor control device and an image forming apparatus. [Background technology]

[0002] Motors such as DC brushless motors, brushed DC motors, and stepping motors are used as drive sources for rotating members used in image forming apparatuses. As DC brushless motors, sensorless motors that do not have a Hall element for detecting the rotational position (rotational phase) of the rotor are also used. In sensorless motors, in order to avoid problems such as loss of synchronism or reverse rotation that may occur when the motor is started, the rotor stop position is detected and a start-up process is performed according to the detected stop position. Patent Document 1 discloses a configuration for detecting the rotor stop position based on the excitation current when a voltage is applied to the coil of the motor for a short period of time. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2015-104263 A Summary of the Invention [Problem to be solved by the invention]

[0004] The rotor stop position can be determined (detected) by generating excitation current in sequence for multiple combinations of coils, measuring the generated excitation current, and based on the measurement results. In this case, the accuracy of rotor stop position determination can be improved by starting measurement from a state where the excitation current is zero. For this reason, if the excitation current decay rate is slow, the waiting time until the excitation current becomes zero becomes long, and the timing at which measurement can be started is delayed, resulting in a longer time required to determine the rotor stop position.

[0005] Furthermore, when the excitation current is regenerated to the power supply in order to attenuate the excitation current in a short time, the energy of the regenerated excitation current increases the output voltage of the power supply. If the output voltage of the power supply changes while the excitation current is measured in sequence for multiple coil combinations, this is one of the factors that reduces the accuracy of determining the rotor stop position. Furthermore, the time required to determine the rotor stop position increases due to the waiting time until the increase in the output voltage of the power supply converges.

[0006] SUMMARY OF THE PRESENT EMBODIMENTS Accordingly, an object of the present invention is to provide a technique for shortening the time required to determine the stopping position of the rotor of a motor to be controlled. [Means for solving the problem]

[0007] A motor control device according to one aspect of the present invention includes: excitation means for exciting an excitation phase to be excited among a plurality of excitation phases of the motor by driving the plurality of switching elements; measurement means for measuring an excitation current flowing through a coil of the excitation phase excited by the excitation means; control means for driving a first switching element connected to a first phase coil of the excitation phase to be excited with a first PWM signal during a first period when exciting the plurality of excitation phases, and for driving a second switching element connected to a second phase coil of the excitation phase with a second PWM signal during a second period after the first period; and determination means for determining a stop position of a rotor of the motor based on a measurement result of the excitation current obtained by the measurement means when exciting the plurality of excitation phases, wherein the control means: In the second period, a PWM signal having a duty ratio that changes in a pattern in which the duty ratio takes a second value larger than the first value at the beginning of the second period and then gradually increases from the first value over time is output to the second switching element. It is characterized by the following features. Effect of the Invention

[0008] According to the present invention, it is possible to reduce the time required to determine the stopping position of the rotor of the motor to be controlled. [Brief description of the drawings]

[0009] [Figure 1]FIG. 1 is a cross-sectional view showing an example of a hardware configuration of an image forming apparatus. [Diagram 2] FIG. 1 is a block diagram showing an example of a control configuration of an image forming apparatus. [Diagram 3] Block diagram showing a configuration example of a motor control unit [Figure 4] A diagram showing an example of a motor configuration [Diagram 5] A diagram showing an example of detection of maximum excitation current and inductance for each excitation phase. [Figure 6] A diagram showing an example of the relationship between inverter drive and the excitation current flowing through the motor. [Figure 7] A diagram showing an example of time variations in PWM signal, excitation current, and voltage of a low-voltage power supply [Figure 8] A diagram showing an example of time variations in PWM signal, excitation current, and voltage of a low-voltage power supply [Figure 9] A diagram showing an example of time variations in PWM signal, excitation current, and voltage of a low-voltage power supply [Figure 10] A diagram showing an example of time variations in PWM signal, excitation current, and voltage of a low-voltage power supply DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, the embodiments will be described in detail with reference to the accompanying drawings. Note that the following embodiments do not limit the invention according to the claims, and not all combinations of features described in the embodiments are essential to the invention. Two or more features among the multiple features described in the embodiments may be arbitrarily combined. In addition, the same reference numbers are used for the same or similar configurations, and duplicated descriptions are omitted.

[0011] [First embodiment] In the first and second embodiments, a case will be described in which a motor control device is provided in an image forming apparatus such as a printing apparatus (printer), a copier, a multifunction machine, or a facsimile machine.

[0012] <Image forming device> FIG. 1 is a cross-sectional view showing an example of the hardware configuration of an image forming apparatus according to the first embodiment. The image forming apparatus 10 forms a full-color image by superimposing toner images of four colors, yellow (Y), magenta (M), cyan (C), and black (K). In FIG. 1, the suffixes Y, M, C, and K of the reference symbols indicate that the colors of the toner images associated with the members indicated by the reference symbols are yellow, magenta, cyan, and black, respectively. In the following description, when it is not necessary to distinguish between colors, the reference symbols are used without the suffixes Y, M, C, and K.

[0013] Image forming apparatus 10 at least includes a photoconductor 11, a charging unit 12, an exposure unit 13, a developing roller 15 (developer), and a primary transfer unit 16 for each color of toner image to be formed. Image forming apparatus 10 further includes at least an intermediate transfer belt 17 (intermediate transfer body), a secondary transfer unit 19, a drive roller 20, a paper feed cassette 21, a transport path 23, a fixing unit 24, and a motor 150. Photoconductor 11, charging unit 12, developing roller 15, primary transfer unit 16, intermediate transfer belt 17, secondary transfer unit 19, and fixing unit 24 constitute an image forming unit that forms an image on a recording material P (sheet) that is fed from paper feed cassette 21 and transported through transport path 23.

[0014] During image formation, the photoconductor 11 is driven to rotate in a clockwise direction in FIG. 1. The charging unit 12 charges the surface of the photoconductor 11 to a uniform potential. The exposure unit 13 exposes the surface of the photoconductor 11 to light based on image data of the image to be formed, forming an electrostatic latent image on the photoconductor 11. The development roller 15 develops the electrostatic latent image on the photoconductor 11 with toner, making the electrostatic latent image visible as a toner image. The primary transfer unit 16 transfers the toner image formed on the photoconductor 11 to the intermediate transfer belt 17 by a primary transfer bias. Note that the toner images formed on the photoconductors 11 are transferred to the intermediate transfer belt 17 in a superimposed manner, forming a full-color image on the intermediate transfer belt 17.

[0015] The intermediate transfer belt 17 is driven to rotate by the drive roller 20 and rotates in a counterclockwise direction in FIG. 1. As a result, the toner image transferred to the intermediate transfer belt 17 is transported to a position facing the secondary transfer unit 19. Meanwhile, a recording material P (sheet) stored in a paper feed cassette 21 is fed to a transport path 23 and transported along the transport path 23 to a position facing the secondary transfer unit 19. The transport path 23 is provided with a transport roller for transporting the recording material P. The secondary transfer unit 19 transfers the toner image on the intermediate transfer belt 17 to the recording material P by a secondary transfer bias. Thereafter, the recording material P is transported to a fixing unit 24. The fixing unit 24 applies heat and pressure to the recording material P to fix the toner image to the recording material P. After the toner image is fixed, the recording material P is discharged to the outside of the image forming apparatus 10.

[0016] In this embodiment, the motor 150 is configured as a DC brushless motor. The driving force of the motor 150 is transmitted to the photoconductor 11, the charging unit 12, the developing roller 15, the primary transfer unit 16, and the driving roller 20 via a gear mechanism (not shown). The driving force of the motor 150 is also transmitted to a conveying roller (rotating member) for conveying the recording material P along the conveying path via the gear mechanism. In this way, the motor 150 is used as a driving source for the conveying roller (rotating member) for conveying the recording material P (sheet) along the conveying path, or as a driving source for an image forming unit that forms an image on the sheet conveyed along the conveying path.

[0017] Fig. 2 is a block diagram showing an example of a control configuration of the image forming apparatus 10. As shown in Fig. 2, the image forming apparatus 10 further includes a control unit 40, a low-voltage power supply 120, sensors 130, a motor control unit 41, a high-voltage power supply 160, a display unit 200, and a communication controller 210. The motor control unit 41 controls the motor 150 according to instructions from the control unit 40.

[0018] The control unit 40 has a microcomputer that uses a microprocessor as a CPU and a memory. The microcomputer controls each device in the image forming apparatus 10 based on various control programs and various data stored in the memory. The sensors 130 are a plurality of sensors for detecting the state of each device in the image forming apparatus 10 or the state of the recording material P.

[0019] The low-voltage power supply 120 is a switching power supply that outputs a DC voltage. The output voltage of the low-voltage power supply 120 is controlled so as to be maintained within a predetermined voltage control range. In addition, the output voltage of the low-voltage power supply 120 is controlled so as to be within the voltage control range even with respect to fluctuations in the load on the low-voltage power supply 120. However, there are cases where the output voltage of the low-voltage power supply 120 cannot follow a sudden load fluctuation. For example, when the load increases suddenly, an undershoot occurs in the output voltage, and when the load decreases suddenly, an overshoot occurs in the output voltage. The DC voltage output by the low-voltage power supply 120 is supplied to each device in the image forming apparatus 10, and is used, for example, to rotate and drive the motor 150.

[0020] The high-voltage power supply 160 generates various bias voltages (e.g., a charging bias voltage, a developing bias voltage, and a transfer bias voltage) required for image formation. The communication controller 210 communicates with an external device such as a host computer 220. For example, the communication controller 210 receives data for printing from the host computer 220.

[0021] When the control unit 40 receives image data of an image to be formed from the host computer 220 via the communication controller 210, it starts forming an image on the recording material P based on the received image data. When the control unit 40 starts forming an image, it controls the motor control unit 41 to rotate the motor 150. As a result, the control unit 40 performs drive control of rotating members such as the photoreceptor 11 and transport control of the recording material P. The control unit 40 controls the exposure unit 13 to form an electrostatic latent image on the photoreceptor 11. The control unit 40 further controls the high-voltage power supply 160 to output bias voltages for image formation to the charging unit 12, the developing roller 15, the primary transfer unit 16, and the secondary transfer unit 19. The control unit 40 also performs display control to display a screen such as a screen showing the state of the image forming apparatus 10 on the display unit 200, and controls the sensors 130 for detecting the state of the recording material P or the image forming apparatus 10.

[0022] <Motor control unit> 3 shows an example of the configuration of the motor control unit 41. In this embodiment, the motor control unit 41 is provided as one component of the image forming apparatus 10, but when configured as one device, it may be called a motor control device. Also, a device including the control unit 40 and the motor control unit 41 may be called a motor control device.

[0023] The motor control unit 41 includes a processing unit 51 and an inverter 60. The processing unit 51 can be realized by a microcomputer or the like. The processing unit 51 has a communication port 52 and a pulse width modulation (PWM) port 58. The processing unit 51 performs serial data communication with the control unit 40 via the communication port 52. In addition, the processing unit 51 outputs a PWM signal for driving each switching element of the inverter 60 via the PWM port 58.

[0024] The inverter 60 is connected to a motor 150 to be controlled by the motor control unit 41. The motor 150 is a three-phase motor having three-phase (U-phase, V-phase, W-phase) windings (coils) 73 to 75. The inverter 60 is a three-phase inverter configured with six switching elements including three high-side switching elements corresponding to the U-phase, V-phase, and W-phase, respectively, and three low-side switching elements corresponding to the U-phase, V-phase, and W-phase, respectively. That is, the inverter 60 includes high-side and low-side switching elements connected to the U-phase coil 73, high-side and low-side switching elements connected to the V-phase coil 74, and high-side and low-side switching elements connected to the W-phase coil 75. Each switching element of the inverter 60 is configured with, for example, a transistor or a FET.

[0025] The PWM port 58 has six terminals respectively corresponding to the six switching elements of the inverter 60. That is, the PWM port 58 has high-side and low-side terminals (UH terminal and UL terminal) corresponding to the U phase, high-side and low-side terminals (VH terminal and VL terminal) corresponding to the V phase, and high-side and low-side terminals (WH terminal and WL terminal) corresponding to the W phase.

[0026] The inverter 60 operates by receiving a DC voltage from the low-voltage power supply 120. Three switching elements on the high side of the inverter 60 are one example of a plurality of switching elements each connected to the low-voltage power supply 120 and each connected to a different coil of the motor 150. Each switching element of the inverter 60 is driven by a PWM signal output from a corresponding terminal of the PWM port 58. The PWM signal output from the PWM port 58 controls the on and off of each switching element of the inverter 60. As a result, a current for excitation flows from the inverter 60 to the coil 73 (U phase), the coil 74 (V phase), and the coil 75 (W phase) of the motor 150. The processing unit 51 controls the on and off of each switching element of the inverter 60 to control the current (excitation current) flowing through each of the coils 73 to 75. In this way, the inverter 60 functions as an excitation unit that excites the coils to be excited among the multiple coils 73 to 75 of the motor 150 (excites the excitation phase to be excited among the multiple excitation phases of the motor 150) by driving multiple switching elements.

[0027] The resistor 63 is used to detect the excitation current supplied to each of the coils 73 to 75. Specifically, the excitation current supplied to each of the coils 73 to 75 is converted into a voltage by the resistor 63. The converted voltage is input to the AD converter 53 of the processing unit 51. The AD converter 53 performs analog / digital (A / D) conversion on the input voltage to convert the input voltage into a digital value, and outputs the digital value as a value indicating the detection result of the excitation current. The non-volatile memory 55 functions as a storage unit that stores data and the like used in processing by the processing unit 51.

[0028] <Motor configuration> 4 shows a specific example of the configuration of the motor 150. The motor 150 has a six-slot stator 71 and a four-pole rotor 72. The stator 71 has three-phase (U-phase, V-phase, W-phase) coils, namely, a U-phase coil 73, a V-phase coil 74, and a W-phase coil 75, and the coils 73 to 75 are connected in a star connection. Each of the coils 73 to 75 is divided into two slots, and the coils in the two slots are connected to each other, for example, by copper wire (not shown). The rotor 72 is made of a permanent magnet and has two sets of N and S poles. The rotor 72 is rotatable about a motor shaft 76.

[0029] In this embodiment, there are six excitation phases in total, UV, UW, VU, VW, WU, and WV, as combinations of coils to be excited among the coils 73 to 75 (i.e., excitation phases). In this specification, for example, "exciting the UV phase" means driving the inverter 60 by a PWM signal output from the PWM port 58 to pass an excitation current from the U-phase coil to the V-phase coil. When the UV phase is excited in this way, an excitation current flows from the U-phase coil 73 to the V-phase coil 74, and at this time, the U-phase coil becomes an N pole and the V-phase coil becomes an S pole.

[0030] Generally, coils such as coils 73 to 75 are configured by winding copper wire around a core made of laminated electromagnetic steel sheets. The magnetic permeability of the electromagnetic steel sheets is reduced when an external magnetic field is present. Since the inductance of a coil is proportional to the magnetic permeability of the core, the inductance of the coil is reduced when the magnetic permeability of the core is reduced. Therefore, the amount of reduction in the inductance of the coil due to the influence of the external magnetic field varies depending on the magnitude of the influence of the external magnetic field. Specifically, the greater the influence of the external magnetic field caused by rotor 72, the greater the amount of reduction in the inductance of the coil.

[0031] 4A, only the S pole of rotor 72 faces U-phase coil 73, and both the S pole and N pole of rotor 72 (the intermediate portion between the S pole and the N pole) face W-phase coil 75. In this case, the U-phase coil 73 is more affected by the external magnetic field caused by rotor 72 than the W-phase coil 75. Therefore, the amount of decrease in inductance of U-phase coil 73 is greater than the amount of decrease in inductance of W-phase coil 75.

[0032] Also, the amount of change in inductance of the coils 73 to 75 differs depending on whether the direction of the magnetic field generated by the excitation current flowing through the coil is the same as or opposite to the direction of the external magnetic field generated by the rotor 72. For example, in the state of FIG. 4(A), when an excitation current is passed in a direction that makes the U phase an N pole, the amount of decrease in inductance of the coil 73 is greater than when an excitation current is passed in a direction that makes the U phase an S pole. Note that when the direction of the magnetic field generated by the excitation current flowing through a certain coil is the same as the direction of the external magnetic field generated by the rotor 72, as in the case of the coil 73 in FIG. 4(A), the amount of decrease in inductance of the coil is the largest. In this way, when the motor 150 is stopped, the inductance of each of the coils 73 to 75 changes depending on the stop position (rotation phase) and excitation phase of the rotor 72.

[0033] Furthermore, when the motor 150 is stopped, the position (rotation phase) at which the rotor 72 stops is determined according to the combination of excited coils (i.e., the excitation phase) among the coils 73 to 75. For example, when the UV phase is excited, an excitation current flows from the U phase coil 73 to the V phase coil 74, and the U phase coil 73 becomes the N pole and the V phase coil 74 becomes the S pole. As a result, the rotor 72 stops at the position shown in FIG. 4(A). Next, when the UW phase is excited, an excitation current flows from the U phase coil 73 to the W phase coil 75, and the U phase coil 73 becomes the N pole and the W phase coil 75 becomes the S pole. As a result, the rotor 72 stops at the position shown in FIG. 4(B).

[0034] As described above, when the rotor 72 is stopped, the inductance (composite inductance) of a certain excitation phase detected when that excitation phase is excited differs depending on the stop position of the rotor 72. When the inductance of the excitation phase differs, the speed of the rise of the excitation current also differs when the excitation current flows through the coil that constitutes that excitation phase.

[0035] FIG. 5 is a diagram showing an example of detection of the maximum value of the excitation current corresponding to each excitation phase and the inductance of each excitation phase, obtained when each excitation phase is excited in sequence while the rotor 72 is stopped at the position shown in FIG. 4(A). The position shown in FIG. 4(A) corresponds to the position where the rotor 72 stops when the UV phase is excited. FIG. 5(A) shows an example of the detection result of the maximum value of the excitation current, obtained by exciting each excitation phase in sequence for a predetermined period and measuring the excitation current when each excitation phase is excited. FIG. 5(B) shows an example of the detection result of the inductance (composite inductance) of each excitation phase, corresponding to the measurement result of the excitation current shown in FIG. 5(A).

[0036] For example, when the UV and VU phases are excited while the rotor 72 is stopped at the position shown in Fig. 4(A), the inductance of each excited phase and the maximum value of the corresponding excitation current are detected as follows. When the VU phase is excited, an excitation current flows from the V phase coil 74 to the U phase coil 73, so that the V phase coil 74 becomes the N pole and the U phase coil 73 becomes the S pole. At this time, as shown in Fig. 4(A), the N pole of the rotor 72 faces the V phase coil 74, and the S pole of the rotor 72 faces the U phase coil 73. In this case, as shown in Fig. 5, the inductance of both the V phase coil 74 and the U phase coil 73 becomes large, the inductance of the VU phase becomes maximum, and the maximum value of the excitation current of the VU phase becomes minimum.

[0037] On the other hand, when the UV phase is excited, an excitation current flows from the U phase coil 73 to the V phase coil 74, so that the U phase coil 73 becomes an N pole and the V phase coil 74 becomes an S pole. At this time, as shown in Fig. 4(A), the U phase coil 73 faces the S pole of the rotor 72, and the V phase coil 74 faces the N pole of the rotor 72. In this case, as shown in Fig. 5, the inductance of both the U phase coil 73 and the V phase coil 74 becomes small, the inductance of the UV phase becomes minimum, and the maximum value of the excitation current becomes maximum.

[0038] Therefore, in this embodiment, each excitation phase is excited in sequence, and the excitation current flowing through the coil constituting each excitation phase is measured, and based on the relative magnitude relationship of the maximum value of the excitation current (or impedance), the stop position of the rotor 72 is determined (estimated). For example, if the maximum value of the excitation current detected when the UV phase is excited is greater than the maximum value of the excitation current detected when any of the other excitation phases is excited, it can be determined that the rotor 72 is stopped at a position corresponding to the UV phase (the position shown in FIG. 4(A)).

[0039] <Relationship between inverter drive and excitation current> Next, with reference to Fig. 6, a description will be given of the drive of the inverter 60 and how an excitation current flows through the motor 150 in accordance with the drive. In this embodiment, in order to determine the stop position of the rotor 72, the excitation phases are excited in sequence for a predetermined time, so that an excitation current flows through the coil constituting the excitation phase to be excited, and the excitation current is measured. Here, the excitation phase to be excited is excited over a first period and a second period following the first period. The following description will be given taking the case of exciting the UV phase as an example.

[0040] First, in the first period, the processing unit 51 outputs a PWM signal having a set duty ratio and alternating between a high (H) level and a low (L) level from the UH terminal of the PWM port 58 to the inverter 60. Also, a voltage having a polarity inverted from that of the voltage output from the UH terminal is output from the UL terminal. That is, when the UH terminal is at the H level, the UL terminal is set to the L level, and when the UH terminal is at the L level, the UL terminal is set to the H level. The VL terminal is set to a constant H level, and the other terminals are set to a constant L level.

[0041] In the first period, the processing unit 51 drives the inverter 60 by the PWM signals output from the UH terminal and the UL terminal of the PWM port 58. FIG. 6(A) shows a case where the output voltage of the UH terminal is at the H level and the output voltage of the UL terminal is at the L level. FIG. 6(B) shows a case where the output voltage of the UH terminal is at the L level and the output voltage of the UL terminal is at the H level. The driving state of the inverter 60 is alternately switched between the state shown in FIG. 6(A) and the state shown in FIG. 6(B). By driving the inverter 60 in this way, an excitation current is generated that flows in the UV phase (i.e., flows in the coils 73 and 74 that constitute the UV phase) as shown by the arrows in FIG. 6(A) and (B).

[0042] When the polarity of the voltages output from the UH terminal and the UL terminal is switched between H level and L level, a period is provided during which the voltages output from both terminals are both at L level in order to prevent a through current from flowing through the switching element of the inverter 60.

[0043] Next, in a second period following the first period, the processing unit 51 drives the inverter 60 so that an excitation current continues to flow through the UV phase. Specifically, the processing unit 51 outputs a PWM signal having a set duty ratio from the VH terminal of the PWM port 58 to the inverter 60. Also, a voltage having a polarity inverted from that of the voltage output from the VH terminal is output from the VL terminal. That is, when the VH terminal is at the H level, the VL terminal is set to the L level, and when the VH terminal is at the L level, the VL terminal is set to the H level. The UL terminal is set to a constant H level, and the other terminals are set to a constant L level.

[0044] In the second period, the processing unit 51 drives the inverter 60 by the PWM signal output from the VH terminal and the VL terminal of the PWM port 58. The driving state of the inverter 60 is alternately switched between the state shown in FIG. 6(C) and the state shown in FIG. 6(D). By driving the inverter 60 in this way, an excitation current flows through the UV phase as shown by the arrows in FIG. 6(C) and (D). FIG. 6(C) shows a case where the output voltage of the VH terminal is at the H level and the output voltage of the VL terminal is at the L level. In this case, as shown by the arrow in FIG. 6(C), the excitation current is regenerated to the low voltage power supply 120 via the switching element connected to the VH terminal. FIG. 6(D) shows a case where the output voltage of the VH terminal is at the L level and the output voltage of the VL terminal is at the H level. In this case, as shown by the arrow in FIG. 6(D), the excitation current is regenerated to the ground via the switching element connected to the VL terminal.

[0045] In the second period, similarly to the first period, when the polarities of the voltages output from the VH terminal and the VL terminal are switched between H level and L level, a period is provided in which the voltages output from both terminals are both at L level in order to prevent a through current from flowing through the switching element of the inverter 60.

[0046] In the state of FIG. 6C, power is stored in the low-voltage power supply 120 by the excitation current regenerated in the low-voltage power supply 120. When the excitation current regenerated in the low-voltage power supply 120 is relatively large, the low-voltage power supply 120 cannot maintain a constant output voltage, causing an overshoot of the output voltage. Therefore, in this embodiment, the duty ratio of the PWM signal output from the VH terminal and the VL terminal of the PWM port 58 to the inverter 60 is adjusted so as to limit the power stored in the low-voltage power supply 120 by the excitation current. Specifically, the duty ratio of the PWM signal is adjusted so that the power stored in the low-voltage power supply 120 is lower than the power supplied by the low-voltage power supply 120 to devices such as the control unit 40, the high-voltage power supply 160, the exposure unit 13, the display unit 200, and the communication controller 210.

[0047] By adjusting the duty ratio of the PWM signal in this way, the power due to the excitation current regenerated in the low-voltage power supply 120 is consumed by the control unit 40, etc. This makes it possible to prevent excessive power from being stored in the low-voltage power supply 120. As a result, it is possible to prevent the output voltage of the low-voltage power supply 120 from fluctuating to a voltage outside a predetermined voltage control range (deviation from the predetermined voltage control range).

[0048] The duty ratio of the PWM signal is adjusted from the following viewpoint. When the power due to the excitation current regenerated in the low-voltage power supply 120 becomes equal to or greater than the power supplied by the low-voltage power supply 120, the low-voltage power supply 120 temporarily stops the power supply. At such a timing, for example, when the power supply from the low-voltage power supply 120 becomes necessary due to a change in the control sequence in the control unit 40, there is a possibility that the regulation of the output voltage will not be able to keep up. As a result, the output voltage of the low-voltage power supply 120 may drop and become a voltage below a predetermined voltage control range. Therefore, in this embodiment, the duty ratio of the PWM signal output from the VH terminal and the VL terminal of the PWM port 58 to the inverter 60 is adjusted so that the power due to the excitation current regenerated in the low-voltage power supply 120 becomes lower than the power supplied by the low-voltage power supply 120.

[0049] <Example of low voltage power supply operation> Next, referring to Fig. 7, an example of the operation of the low-voltage power supply 120 when the output voltage of the low-voltage power supply 120 deviates from a predetermined voltage control range due to regeneration of the excitation current to the low-voltage power supply 120 will be described. Fig. 7 shows the time changes of the PWM signals output from the UH terminal and the VH terminal of the PWM port 58, the excitation current of the UV phase, and the output voltage and the supply power of the low-voltage power supply 120 when the UV phase and the VU phase are excited in order to determine the stop position of the rotor 72. Note that in the figure, the time changes of the duty ratio of each PWM signal are shown for the PWM signals. Also, for the UV phase excitation current, a positive value indicates the case where the excitation current flows from the U phase coil 73 to the V phase coil 74, and a negative value indicates the case where the excitation current flows in the opposite direction, from the V phase coil 74 to the U phase coil 73.

[0050] As shown in Fig. 7, in the first first and second periods, for excitation of the UV phase, a PWM signal whose duty ratio changes in a measurement pattern is outputted in the order of the UH terminal and the VH terminal of the PWM port 58. In the next first and second periods, for excitation of the VU phase, a PWM signal whose duty ratio changes in a measurement pattern is outputted in the order of the VH terminal and the UH terminal of the PWM port 58. In the example of Fig. 7, a PWM signal whose duty ratio changes in a sinusoidal pattern is used for both excitation of the UV phase and the VU phase.

[0051] 7, the output voltage of the low-voltage power supply 120 during the period in which the VU phase is excited is different from the output voltage during the period in which the UV phase is excited. If the voltages output from the low-voltage power supply 120 differ when each excitation phase is excited in this way, the accuracy of determining the stop position of the rotor 72 decreases. For this reason, in order to accurately determine the stop position of the rotor 72, it is necessary to pass an excitation current through (the coil constituting) the excitation phase to be excited while the output voltage of the low-voltage power supply 120 is constant (at least within a predetermined voltage control range).

[0052] In addition, when the output voltage of the low-voltage power supply 120 deviates from the predetermined voltage control range due to the regeneration of the exciting current, the power supply may stop. When the inverter 60 is driven in this state to pass an exciting current through the motor 150, the regulation of the output voltage of the low-voltage power supply 120 is not in time, and the output voltage of the low-voltage power supply 120 drops sharply. In the example of FIG. 7, in the second first period (the first period for exciting the V-U phase) after T1, the output voltage of the low-voltage power supply 120 has dropped to a voltage lower than the predetermined voltage control range. Such a sharp drop in the output voltage of the low-voltage power supply 120 also causes a decrease in the determination accuracy of the stop position of the rotor 72.

[0053] In order to avoid a decrease in the determination accuracy of the stop position of the rotor 72 when the output voltage of the low-voltage power supply 120 deviates from the voltage control range in this way, it is necessary to wait for the output voltage of the low-voltage power supply 120 to return within the voltage control range and then perform excitation of the exciting phase of the next excitation target. However, when such a waiting time occurs, the time required for determining the stop position of the rotor 72 becomes longer. Therefore, in the present embodiment, by suppressing the fluctuation of the output voltage of the low-voltage power supply 120, it is possible to shorten the time until the exciting phase of the next excitation target is excited for determining the stop position of the rotor 72.

[0054] <Adjustment of the duty ratio of the PWM signal> Next, with reference to FIG. 8, the control of the PWM signals output from the U-H terminal and the V-H terminal of the PWM port 58 in the present embodiment will be described. FIG. 8 shows the time changes of the PWM signals output from the U-H terminal and the V-H terminal of the PWM port 58, the exciting current of the U-V phase, the output voltage and the supplied power of the low-voltage power supply 120 when the U-V phase is excited for determining the stop position of the rotor 72. In the example of FIG. 8, the PWM signal output from the U-H terminal is an example of the first PWM signal output to the first switching element connected to the coil of the first phase of the exciting phase of the excitation target. Further, the PWM signal output from the V-H terminal is an example of the second PWM signal output to the second switching element connected to the coil of the second phase of the exciting phase of the excitation target.

[0055] In the first period in which the U-V phases are excited, the processing unit 51 outputs a PWM signal whose duty ratio changes over time as shown in Fig. 8 from the UH terminal of the PWM port 58 to the inverter 60. Specifically, in the first period, as shown in Fig. 8, a PWM signal whose duty ratio changes in a sinusoidal pattern is output from the UH terminal. Note that, as shown in Figs. 6(A) and (B), in the first period, the output voltage of the VL terminal of the PWM port 58 is set to a constant H level (duty ratio of 100%). Also, the output voltages of the other terminals are set to a constant L level (duty ratio of 0%).

[0056] Such driving of the inverter 60 generates an excitation current in the UV phase, and as the power supply of the low-voltage power supply 120 increases, the output voltage of the low-voltage power supply 120 temporarily drops. This temporary voltage drop occurs every time each excitation phase is excited in sequence (within the voltage control range), and does not affect the accuracy of determining the stop position of the rotor 72.

[0057] Then, in a second period following the first period, the processing unit 51 outputs a PWM signal whose duty ratio changes in a pattern that increases (monotonically increases) over time from the VH terminal of the PWM port 58, as shown in Fig. 8. Note that, as shown in Fig. 6(C) and (D), in the second period, the output voltage of the U-L terminals of the PWM port 58 is set to a constant H level (duty ratio of 100%). Also, the output voltages of the other terminals are set to a constant L level (duty ratio of 0%).

[0058] In the second period, the excitation current flowing through each of the coils 73 to 75 decreases over time due to the power supply (regeneration) to the low-voltage power supply 120 and power consumption due to the resistance of each coil. For this reason, in this embodiment, the duty ratio of the PWM signal output from the VH terminal of the PWM port 58 in the second period is changed in a pattern that increases over time. This makes it possible to maintain the power supplied to the low-voltage power supply 120 constant, and to converge the excitation current to 0 in a short time. As a result, it is possible to prevent the occurrence of fluctuations in the output voltage of the low-voltage power supply 120 as shown in FIG. 7, and it is possible to shorten the time until the excitation of the next excitation target excitation phase is started in order to determine the stop position of the rotor 72.

[0059] As described above, pattern data for changing the duty ratio of the PWM signal output from each terminal of the PWM port 58 is created in advance and stored in the non-volatile memory 55 so that the output voltage of the low-voltage power supply 120 does not deviate from the voltage control range. This pattern data indicates a pattern for changing the duty ratio of the PWM signal over time. For example, the PWM signal pattern is designed by measuring the amount of fluctuation in the power supplied by the low-voltage power supply 120 through an experiment performed in advance, and based on the measurement results, a pattern for increasing or decreasing the duty ratio of the PWM signal according to the increase or decrease in the supplied power is designed. That is, the duty ratio pattern is created in advance based on the measurement results of the fluctuation in the power supplied by the low-voltage power supply 120 due to the fluctuation in the load connected to the low-voltage power supply 120.

[0060] Also, a plurality of different patterns may be created corresponding to each of a plurality of control sequences of the control unit 40. In this case, the processing unit 51 determines (changes) a pattern to be used from among a plurality of patterns indicated by the pattern data stored in the non-volatile memory 55 in accordance with the operating state of the image forming apparatus 10 in order to optimize the damping rate of the excitation current. For example, the processing unit 51 determines a pattern to be used from among a plurality of patterns stored in the non-volatile memory 55 based on the power supplied by the low-voltage power supply 120.

[0061] For example, when the motor control unit 41 controls a plurality of motors and a motor other than the motor to be determined is rotating when determining the stop position of the rotor 72, the power supplied by the low-voltage power supply 120 increases. At that time, the processing unit 51 outputs a PWM signal to the inverter 60 using a pattern having a relatively larger duty ratio than other patterns in the second period, thereby attenuating the excitation current in a short time. This suppresses fluctuations in the output voltage of the low-voltage power supply 120, shortens the time until excitation of the next excitation phase to be excited is started, and makes it possible to shorten the time required to determine the stop position of the rotor 72.

[0062] In the present embodiment, as shown in FIG. 8, an example has been shown in which the above-mentioned first period and second period are continuous, but a period in which no PWM signal is output from each terminal of the PWM port 58 may be provided between the first period and the second period.

[0063] As described above, in this embodiment, when exciting a plurality of excitation phases, the processing unit 51 drives the first switching element connected to the first-phase coil of the excitation phase to be excited by the first PWM signal during the first period. The processing unit 51 further drives the second switching element connected to the second-phase coil of the excitation phase by the second PWM signal during the second period after the first period. For example, when exciting the UV phase among the six excitation phases, the processing unit 51 drives the switching element connected to the first-phase (U-phase) coil 73 of the UV phase by the first signal during the first period. Furthermore, the processing unit 51 drives the switching element connected to the second-phase (V-phase) coil 74 of the UV phase by the second PWM signal during the second period after the first period. The processing unit 51 measures the excitation current flowing through the coil of the excitation phase excited by the inverter 60 using the resistor 63 and the AD converter 53. The processing unit 51 determines the stop position of the rotor of the motor 150 based on the measurement result of the excitation current obtained by exciting a plurality of excitation phases.

[0064] When exciting the multiple excitation phases as described above, the processing unit 51 controls the duty ratio of the second PWM signal output to the second switching element in the second period based on the supply power supplied by the low-voltage power supply 120. More specifically, the processing unit 51 controls the duty ratio of the second PWM signal so that the power due to the excitation current regenerated in the low-voltage power supply 120 via the second switching element in the second period falls below the supply power of the low-voltage power supply 120.

[0065] This makes it possible to prevent the power supply from the low-voltage power supply 120 from being stopped due to excessive power being stored in the low-voltage power supply 120 due to the power from the excitation current regenerated in the low-voltage power supply 120. Therefore, fluctuations in the output voltage of the low-voltage power supply 120 are suppressed, and in measuring the excitation current for determining the stop position of the rotor 72, it is possible to shorten the time until excitation of the next excitation phase to be excited is started, and to shorten the time required to determine the stop position of the rotor 72.

[0066] [Second embodiment] In the first embodiment, an example was described in which pattern data indicating a pattern of the duty ratio of the PWM signal output from the processing unit 51 is created in advance and stored in the non-volatile memory 55. In the second embodiment, the control unit 40 monitors the power supply of the low-voltage power supply 120, and changes the pattern of the duty ratio of the PWM signal output from the PWM port 58 of the processing unit 51 in response to a change in the power supply. In the following, a description of parts common to the first embodiment will be omitted.

[0067] In this embodiment, the control unit 40 monitors the power supplied by the low-voltage power supply 120. When the power supplied by the low-voltage power supply 120 increases, the control unit 40 changes the pattern data used by the processing unit 51 so that the duty ratio of the PWM signal used in the above-mentioned second period increases.

[0068] For example, when exciting the UV phase, if the power supplied by the low-voltage power supply 120 increases in the second period as shown in Fig. 9, the duty ratio of the PWM signal output from the VH terminal of the PWM port 58 is increased in response to the increase in the supplied power. As a result, the excitation current flowing through the coils 73 and 74 constituting the UV phase is attenuated in a short time by being regenerated in the low-voltage power supply 120. At that time, the duty ratio of the PWM signal output from the VH terminal of the PWM port 58 is adjusted so that the power due to the excitation current regenerated in the low-voltage power supply 120 is lower than the supply power supplied by the low-voltage power supply 120.

[0069] This suppresses fluctuations in the output voltage of the low-voltage power supply 120, making it possible to further shorten the time until excitation of the next excitation phase to be excited begins, and further shortening the time required to determine the stopping position of the rotor 72.

[0070] The control unit 40 may monitor the voltage output by the low-voltage power supply 120 instead of the power supplied by the low-voltage power supply 120. When the power supplied by the low-voltage power supply 120 increases, the output voltage of the low-voltage power supply 120 temporarily drops. For this reason, the control unit 40 detects such a drop in the output voltage and increases the duty ratio of the PWM signal output from the VH terminal of the PWM port 58 accordingly. As a result, as described above, the excitation current flowing through the coils 73 and 74 constituting the UV phase is attenuated in a short time by being regenerated in the low-voltage power supply 120. At that time, the control unit 40 adjusts the duty ratio of the PWM signal output from the VH terminal of the PWM port 58 so that the output voltage of the low-voltage power supply 120 does not exceed the reference voltage. As a result, as in the above example, the fluctuation of the output voltage of the low-voltage power supply 120 is suppressed, and the time until the excitation of the next excitation target excitation phase is started can be further shortened, and the time required to determine the stop position of the rotor 72 can be further shortened.

[0071] [Other embodiments] Various modifications are possible to the first and second embodiments described above. For example, FIG. 10 shows another example of the pattern of the duty ratio of the PWM signal output from the VH terminal of the PWM port 58 in the second period described with reference to FIG. 8. FIG. 10 shows an example in which the duty ratio of the PWM signal output from the VH terminal of the PWM port 58 is increased only at the beginning of the second period, and the duty ratio is gradually increased from a small value thereafter. Specifically, the processing unit 51 may output to the second switching element, in the second period, a PWM signal whose duty ratio changes in a pattern in which the duty ratio takes a second value larger than the first value at the beginning of the second period, and then gradually increases from the first value over time. In the example shown in FIG. 10, as an example, the first value is set to 0% and the second value is set to 100%.

[0072] By changing the duty ratio of the PWM signal output from the VH terminal of the PWM port 58 in the second period as described above, the power regenerated in the low-voltage power supply 120 increases (compared to the example shown in FIG. 8). This allows the UV-phase excitation current to converge more quickly, as shown in FIG. 10, and makes it possible to further shorten the time required to determine the stop position of the rotor 72.

[0073] In each of the above-described embodiments, the length of the second period may be adjusted based on a change in the excitation current measured for the excitation phase of the excitation target. For example, in the examples shown in Fig. 8, Fig. 9, and Fig. 10, the length of the second period may be adjusted to a shorter period depending on the time it takes for the excitation current of the UV phase to converge to 0. This makes it possible to further reduce the time required to determine the stop position of the rotor 72.

[0074] In addition, in each of the above-described embodiments, it is not necessary to excite all of the excitation phases of the motor 150 in determining the stop position of the rotor 72. In other words, only some of the six excitation phases of the motor 150 may be excitation targets for determining the stop position of the rotor 72, as long as the determination is possible based on the measurement results of the obtained excitation current.

[0075] The motor control unit 41 in each of the above-described embodiments can be implemented as a motor control device. Alternatively, the motor control unit 41 and the parts of the control unit 40 related to motor control can be implemented as a motor control device. The present invention can also be applied to, for example, any of a motor that drives each roller related to sheet transport in an image forming apparatus, and a motor that rotates and drives a rotating member in an image forming unit of an image forming apparatus.

[0076] 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.

[0077] 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]

[0078] 10: image forming apparatus, 40: control unit, 41: motor control unit, 52: communication port, 58: PWM port, 60: inverter, 73 to 75: coils, 150: motor

Claims

1. A motor control device, an excitation means including a plurality of switching elements each connected to a power source and connected to a different coil of a motor, the plurality of switching elements being driven to excite an excitation phase to be excited among a plurality of excitation phases of the motor; a measuring means for measuring an excitation current flowing through a coil of an excitation phase excited by the exciting means; a control means for driving a first switching element connected to a first-phase coil of an excitation phase to be excited by a first PWM signal during a first period when exciting the plurality of excitation phases, and for driving a second switching element connected to a second-phase coil of the excitation phase by a second PWM signal during a second period following the first period; a determination means for determining a stop position of the rotor of the motor based on a measurement result of an excitation current by the measurement means, the measurement result being obtained by exciting the plurality of excitation phases; The control means outputs to the second switching element, in the second period, a PWM signal whose duty ratio changes in a pattern in which the duty ratio takes a second value larger than the first value at the beginning of the second period and then gradually increases from the first value over time. A motor control device comprising:

2. A motor control device, an excitation means including a plurality of switching elements each connected to a power source and connected to a different coil of a motor, the plurality of switching elements being driven to excite an excitation phase to be excited among a plurality of excitation phases of the motor; a measuring means for measuring an excitation current flowing through a coil of an excitation phase excited by the exciting means; a control means for driving a first switching element connected to a first-phase coil of an excitation phase to be excited by a first PWM signal during a first period when exciting the plurality of excitation phases, and for driving a second switching element connected to a second-phase coil of the excitation phase by a second PWM signal during a second period following the first period; a determination means for determining a stop position of the rotor of the motor based on a measurement result of an excitation current by the measurement means, the measurement result being obtained by exciting the plurality of excitation phases; a memory means for storing a pattern indicating a change over time in the duty ratio of a PWM signal, the pattern being created in advance based on a measurement result of a change in the power supply supplied by the power supply in association with a change in a load connected to the power supply; The control means outputs, during the second period, a PWM signal whose duty ratio changes according to the pattern stored in the storage means to the second switching element. A motor control device comprising:

3. The storage means stores a plurality of different patterns, The control means determines a pattern to be used from among the plurality of patterns based on the power supplied by the power source.

3. The motor control device according to claim 2.

4. A motor control device, an excitation means including a plurality of switching elements each connected to a power source and connected to a different coil of a motor, the plurality of switching elements being driven to excite an excitation phase to be excited among a plurality of excitation phases of the motor; a measuring means for measuring an excitation current flowing through a coil of an excitation phase excited by the exciting means; a control means for driving a first switching element connected to a first-phase coil of an excitation phase to be excited by a first PWM signal during a first period when exciting the plurality of excitation phases, and for driving a second switching element connected to a second-phase coil of the excitation phase by a second PWM signal during a second period following the first period; a determination means for determining a stop position of the rotor of the motor based on a measurement result of an excitation current by the measurement means, the measurement result being obtained by exciting the plurality of excitation phases; A monitoring means for monitoring the power supply provided by the power supply, The control means changes a duty ratio of the second PWM signal output to the second switching element during the second period in response to a change in the supply power monitored by the monitoring means. A motor control device comprising:

5. The control means increases a duty ratio of the second PWM signal output to the second switching element in the second period in response to an increase in the supplied power.

5. The motor control device according to claim 4.

6. The control means further adjusts the length of the second period in response to a change in the excitation current measured by the measurement means.

6. The motor control device according to claim 1, wherein the first and second motors are connected to each other.

7. An image forming apparatus, 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; The motor control device according to claim 1 , which controls the motor; An image forming apparatus comprising:

Images