Image forming apparatus

Abstract

To reduce the time required for detection of a rotor stop position.SOLUTION: An image forming apparatus performs measurement processing of controlling coil current to flow from a first coil to a second coil, of at least three coils of a motor, to measure a current value, on a plurality of excitation phases that are specified by the linear arrangement of two coils of the at least three coils, thereby detecting a rotor stop position. In a first period of the measurement processing, the image forming apparatus controls the coil current to flow from the first coil toward the second coil, in a second period subsequent to the first period, controls the coil current to be attenuated, and in a third period within the second period, controls part of the coil current to flow to a third coil, which is included in the at least three coils and different from the first coil and second coil, from a second terminal of the second coil through a second terminal of the third coil.SELECTED DRAWING: Figure 6

Description

[Technical field]

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

[0002] A sensorless DC brushless motor that is not equipped with a sensor for detecting the rotor position is used as a drive source for a rotating member in an image forming apparatus. In order to prevent loss of synchronism or reverse rotation at startup, the sensorless DC brushless motor detects the rotor stop position (hereinafter, rotor stop position) and performs startup processing according to the rotor stop position. Patent Document 1 discloses a configuration in which an excitation current (coil current) is passed through each of a plurality of excitation phases of a motor, and the rotor stop position is detected based on the current value of the coil current that flows when each excitation phase is excited. [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] In an image forming apparatus, the time required for printing can be shortened by shortening the motor start-up time. In order to shorten the motor start-up time, it is effective to shorten the time required for detecting the rotor stop position. In order to detect the rotor stop position, it is necessary to pass a coil current through each of a plurality of excitation phases and measure the current value, but measurement for a certain excitation phase cannot be started until the current value of the coil current passed through the previous excitation phase has become sufficiently small. Therefore, the time required for detecting the rotor stop position can be shortened by quickly attenuating the coil current passed through a certain excitation phase.

[0005] However, if an attempt is made to speed up the decay of the coil current, the regenerative current to the power supply will increase, which may raise the power supply voltage. It is possible to suppress the regenerative current by increasing the capacity of the electrolytic capacitor connected to the power supply line, but this increases the cost and size of the image forming apparatus.

[0006] The present invention provides a technique capable of shortening the time required to detect the rotor stop position. [Means for solving the problem]

[0007] According to one aspect of the present invention, an image forming apparatus for forming an image on a sheet conveyed along a conveying path includes a rotating member, a motor for driving the rotating member, the motor having at least three coils, first terminals of the at least three coils being connected to each other, and a motor control unit for controlling the motor by controlling a potential of a second terminal different from the first terminals of the at least three coils, the second terminal being connected to the first terminals of the at least three coils, the motor control unit controlling the motor by controlling a potential of a second terminal different from the first terminals of the at least three coils, the measurement process being performed for each of a plurality of excitation phases specified by a permutation of two coils of the at least three coils to measure a current value of the coil current, and a motor control means for detecting a stop position of a rotor of a motor, wherein the motor control means controls the coil current to flow from the first coil to the second coil during a first period of the measurement process, controls the coil current that flowed from the first coil to the second coil during the first period to be attenuated during a second period following the first period, and controls the coil current to flow from the first coil to the second coil during a third period within the second period to flow from the second terminal of the second coil to the third coil via the second terminal of a third coil different from the first coil and the second coil among the at least three coils. Effect of the Invention

[0008] According to the present invention, the time required to detect the rotor stop position can be reduced. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is a block diagram of an image forming apparatus according to some embodiments. [Diagram 2] FIG. 2 is a control configuration diagram of an image forming apparatus according to some embodiments. [Diagram 3] FIG. 2 is a block diagram of a motor controller, according to some embodiments. [Figure 4] FIG. 2 is a block diagram of a motor, according to some embodiments. [Diagram 5] FIG. 4 illustrates a relationship between excitation phase and composite impedance, according to some embodiments. [Figure 6] 4A-4C are diagrams illustrating PWM signals and coil currents according to some embodiments. [Figure 7] 4A-4C are diagrams illustrating PWM signals and coil currents according to some embodiments. [Figure 8] 4A and 4B are diagrams illustrating duty data according to some embodiments. [Figure 9] FIG. 4 is a diagram showing the relationship between the excitation phase and the maximum value of the coil current according to some embodiments. [Figure 10] 13 is a flow chart of a rotor stop position detection process according to some embodiments. [Figure 11] 11 is a flow chart of a duty factor update process according to some embodiments. [Figure 12] 4A-4C are diagrams illustrating PWM signals and coil currents according to some embodiments. [Figure 13] 4A and 4B are diagrams illustrating duty data according to some embodiments. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, the embodiments will be described in detail with reference to the attached drawings. Note that the following embodiments do not limit the invention according to the claims. Although the embodiments describe a number of features, not all of these features are essential to the invention, and the features may be combined in any manner. Furthermore, in the attached drawings, the same reference numbers are used for the same or similar configurations, and duplicated descriptions are omitted.

[0011] First Embodiment FIG. 1 is a configuration diagram of an image forming apparatus according to the present embodiment. The image forming apparatus may be, for example, a printing apparatus, a printer, a copier, a multifunction machine, or a facsimile machine. A sheet stored in a cassette 25 of the image forming apparatus is conveyed along a conveying path by a feed roller 26 and a conveying roller 27. The image forming unit 1 forms yellow, magenta, cyan, and black toner images, and transfers these toner images to a sheet conveyed along the conveying path. The fixing device 24 has a heating roller and a pressure roller, and heats and presses the sheet to which the toner image has been transferred, thereby fixing the toner image to the sheet. The sheet to which the toner image has been fixed is discharged to the outside of the image forming apparatus. The motor 15F is a drive source that rotates the roller of the fixing device 24. The motor 15F may be a sensorless motor that does not have a sensor for detecting the rotor position. The image forming apparatus shown in FIG. 1 is a color image forming apparatus that forms an image using four color toners, but the image forming apparatus may be, for example, a monochrome image forming apparatus that forms an image using only black toner. Moreover, the image forming apparatus in FIG. 1 is an electrophotographic image forming apparatus, but the image forming apparatus may be an inkjet type or any other type of image forming apparatus.

[0012] FIG. 2 shows the control configuration of the image forming apparatus. When the printer control unit 11 receives image data of an image to be formed from the host computer 22 via the communication controller 21, it controls the image forming unit 1 to form a toner image on a sheet, and controls the fixing device 24 to fix the toner image on the sheet. At this time, the printer control unit 11 controls the motor control unit 14 to control the rotation of each motor 15 including the motor 15F. The motor 15 is, for example, a driving source for the roller of the fixing device 24, the roller of the conveying unit that conveys the sheet along the conveying path, and the rotating members included in the image forming unit 1. The conveying unit includes, for example, a feed roller 26 and a conveying roller 27. The rotating members of the image forming unit 1 include, for example, a photoconductor, a developing roller, and the like. Furthermore, the printer control unit 11 displays the state of the image forming apparatus on the display unit 20. The printer control unit 11 includes, for example, one or more processors and a memory. The memory holds various control programs and data, and one or more processors control each section of the image forming apparatus based on the various control programs and data stored in the memory.

[0013] FIG. 3 shows an example of the configuration of the motor control unit 14. The motor control unit 14 has a microcomputer (hereinafter, referred to as a microcomputer) 51. The microcomputer 51 communicates with the printer control unit 11 via a communication port 52. The microcomputer 51 outputs a pulse width modulation signal (PWM signal) from a PWM port 58. In this embodiment, the microcomputer 51 outputs a total of six PWM signals, including high-side PWM signals (UH, VH, WH) and low-side PWM signals (UL, VL, WL), for each of the three-phase coils (U phase, V phase, W phase) of the motor 15F. For this reason, the PWM port 58 has six terminals UH, VH, WH, UL, VL, WL. Each terminal of the PWM port 58 is connected to a gate driver 61.

[0014] The inverter 60 has six switching elements in total, each of which corresponds one-to-one to the PWM signals output from the PWM port 58. That is, the inverter 60 has switching elements corresponding to UH, VH, WH, UL, VL, and WL. For example, FETs can be used as the switching elements. The gate driver 61 performs ON / OFF control of the switching elements of the inverter 60 corresponding to the PWM signal based on the PWM signal from the PWM port 58. In this embodiment, when the PWM signal is high, the corresponding switching element is turned ON, and when the PWM signal is low, the corresponding switching element is turned OFF. The output 62 of the inverter 60 is connected to second terminals of coils 73 (U phase), 74 (V phase), and 75 (W phase) of the motor. The first terminals different from the second terminals of the coils 73, 74, and 75 are connected to each other to form a neutral point 76. The motor 15F has a rotor 72.

[0015] The inverter 60 is connected to a power supply terminal 66 (third terminal) that is connected to a DC power supply (not shown), and the inverter 60 and the motor 15F operate on power from this DC power supply. The potential of the power supply terminal 66 is, for example, +24 V. A bulk electrolytic capacitor 65 is connected in parallel with the inverter 60 between the power supply terminal 66 and a ground terminal 67 (fourth terminal). The bulk electrolytic capacitor 65 absorbs regenerative current and supplies current to the inverter 60.

[0016] The microcomputer 51 controls each switching element of the inverter 60 with a PWM signal, thereby controlling the voltage applied to each of the coils 73 to 75. In this way, the microcomputer 51 controls the rotation of the motor 15F by adjusting the current value of the coil current flowing through each of the coils 73 to 75. In other words, the microcomputer 51 and the inverter 60 control the potential of the second terminal of each of the coils of the motor 15F to control the rotation of the motor 15F.

[0017] The coil currents flowing through the coils 73, 74, and 75 are converted into voltages by resistors 63 corresponding to the U, V, and W phases, respectively. The voltages of the resistors 63 corresponding to the U, V, and W phases, respectively, are input to the AD converter 53 of the microcomputer 51 via the amplifier 64. The terminal of the resistor 63 other than the terminal connected to the inverter 60 is connected to a ground terminal 67. The AD converter 53 converts the input voltage into a digital value. The microcomputer 51 detects the current value of the coil currents flowing through the coils 73, 74, and 75 based on the digital value. In this way, the resistors 63, the amplifier 64, and the microcomputer 51 constitute a current detection unit that detects the current value of the coil currents. The microcomputer 51 also has a non-volatile memory 55 that stores various data and the like used for controlling the motor 15F, and a volatile memory 57.

[0018] Each of the coils 73, 74, 75 can be set to one of a first state, a second state, and a third state by the switching elements of the inverter 60. The first state is a state in which only the high-side switching element corresponding to the coil is turned on to connect the second terminal of the coil to the power terminal 66 at a first potential (for example, +24 V). The second state is a state in which only the low-side switching element corresponding to the coil is turned on to connect the second terminal of the coil to the ground terminal 67 at a second potential (for example, ground potential) lower than the first potential via the resistor 63. The third state is a state in which both the high-side and low-side switching elements corresponding to the coil are turned off to connect the second terminal of the coil to neither the power terminal 66 nor the ground terminal 67, that is, a state in which the second terminal is open. In this way, the inverter 60 functions as a setting unit that sets the state of each coil to one of the first state, the second state, and the third state, or as a switching unit that switches between the first state, the second state, and the third state.

[0019] FIG. 4 is a diagram showing a configuration example of the motor 15F. The motor 15F has a 6-slot stator 71 and a 4-pole rotor 72. The stator 71 is provided with a U-phase coil 73, a V-phase coil 74, and a W-phase coil 75. The rotor 72 is made of a permanent magnet and has two pairs of N and S poles. The position at which the rotor 72 stops is determined according to the excitation phase. In this embodiment, the excitation phase is specified by the permutation of two coils among the coils 73, 74, and 75. That is, there are six excitation phases in total, UV, UW, VU, VW, WU, and WV. Here, exciting the UV phase means exciting the coil so that a coil current flows from the U-phase coil 73 to the V-phase coil 74 via the neutral point 76. For example, when the UV phase is excited, the rotor 72 stops at the rotation position shown in FIG. 4(A). At this time, the U phase becomes an N pole and the V phase becomes an S pole. When the UW phase is subsequently excited, the rotor 72 stops at the rotation position shown in FIG.

[0020] When the driving of the motor 15F is stopped and the coil current is set to 0, the force holding the rotor 72 is no longer working, and the rotor 72 will rotate if a rotational force is applied to the rotor 72 from the outside. Therefore, the rotor 72 can rotate when the fixing unit 24 is detached from the image forming apparatus, or when a sheet caught in the fixing unit 24 due to a jam is removed. At this time, the motor control unit 14 cannot determine the stopping position of the rotor 72. Also, even immediately after the image forming apparatus is powered on, the motor control unit 14 cannot determine the stopping position of the rotor 72. Therefore, when the motor control unit 14 rotates the motor 15F, it first performs a process of detecting the stopping position of the rotor 72.

[0021] Generally, coils such as coils 73, 74, and 75 are configured by winding copper wire around a core made of laminated electromagnetic steel sheets. The magnetic permeability of the electromagnetic steel sheets decreases when there is an external magnetic field. Since the inductance of a coil is proportional to the magnetic permeability of the core, the smaller the magnetic permeability of the core, the smaller the inductance of the coil. For example, since only the S pole of the rotor 72 faces the U-phase coil 73 in FIG. 4(A), the inductance decreases more than the W-phase coil 75, which faces both the S pole and the N pole of the rotor 72. The amount of change in inductance differs depending on whether the direction of the magnetic field generated by the coil current is the same as or opposite to the direction of the external magnetic field. Specifically, in the state of FIG. 4(A), if a coil current is passed through the U-phase coil 73 in the same direction as the magnetic field generated by the opposing S pole of the rotor 72, that is, so that the U phase becomes the N pole, the amount of decrease in inductance is greater than when a coil current is passed through the U-phase coil 73 in the direction so that the U phase becomes the S pole. In this way, the detected inductance value differs depending on the stop position of the rotor 72 and the excitation phase. In addition, as the inductance changes, the iron loss of the coil changes, and the resistance component of the coil also changes. Hereinafter, the inductance component and resistance component of the coil will be collectively referred to as the coil impedance.

[0022] FIG. 5 shows the composite impedance observed by exciting each excitation phase when the rotor 72 is at a position where it will stop when the UV phase is excited. Hereinafter, the position where the rotor 72 stops when the XY phase is excited is expressed as the "position of the XY phase". Since the rotor 72 stops at the position of the UV phase, the composite impedance when the UV phase is excited is smaller than the composite impedance when the other excitation phases are excited. Therefore, if the relative magnitude relationship of the composite impedance of each excitation phase is known, the position of the rotor 72 can be determined. In this embodiment, as described below, a measurement process of exciting the excitation phase and measuring the coil current is performed for each excitation phase in sequence. Then, the stop position of the rotor 72 is detected based on the current value of the coil current measured for each excitation phase.

[0023] The measurement process for each excitation phase is similar, and the measurement process for the UV phase will be described below as a representative example. The coil 73 (first coil) of the U phase and the coil 74 (second coil) of the V phase, which are excitation targets in the measurement process for the UV phase, will be referred to as excitation coils below, and the coil 75 (third coil) of the W phase, which is not included in the excitation phase, will be referred to as a non-excitation coil. As shown in FIG. 6, the period of the measurement process for one excitation phase is divided into period A (first period) and period B (second period). Furthermore, period C (third period) is set within period B. Period A is a period in which the inverter 60 is controlled so that a coil current flows from the coil 73 of the U phase to the coil 74 of the V phase. On the other hand, period B is a period in which the inverter 60 is controlled so that the coil current that flows from the coil 73 of the U phase to the coil 74 of the V phase in period A is attenuated. Ideally, the coil current value becomes 0 at the end timing of period B, but in reality, the coil current value can be positive or negative at the end timing of period B. When the current value is positive, the coil current flows from the U-phase coil 73 to the V-phase coil 74. On the other hand, when the current value is negative, the coil current flows from the V-phase coil 74 to the U-phase coil 73.

[0024] First, the period A will be described. In the period A, the microcomputer 51 outputs a PWM signal whose high-level duty cycle changes in a sinusoidal manner from the UH terminal. Although not shown, the microcomputer 51 outputs a PWM signal (hereinafter, a complementary PWM signal) whose polarity is inverted from the PWM signal output from the UH terminal from the UL terminal. Therefore, in the period A, the second terminal of the U-phase coil 73 is connected to the power supply terminal 66 during the period when the PWM signal output from the UH terminal is at a high level, and is connected to the ground terminal 67 via the resistor 63 during the period when the PWM signal is at a low level. That is, in the period A, the U-phase coil 73 is alternately set to the first state and the second state. Note that the setting period (third setting period) from when the U-phase coil 73 is set to the first state to when it is set to the second state corresponds to the high-level period of the PWM signal output from the UH terminal. As shown in FIG. 6, this setting period increases with the passage of time in the period A, and then decreases.

[0025] Furthermore, in period A, microcomputer 51 outputs a low level (duty is 0%) from the VH terminal and the WH terminal. Although not shown, in period A, microcomputer 51 outputs a high level (duty is 100%) from the VL terminal, thereby connecting the second terminal of V-phase coil 74 to ground terminal 67 via resistor 63. Furthermore, although not shown, microcomputer 51 outputs a low level from the WL terminal. In other words, in period A, V-phase coil 74 is set to the second state, and W-phase coil 75 is set to the third state.

[0026] In a period B (second period) following the period A, the microcomputer 51 outputs a PWM signal whose high-level duty changes in a sinusoidal manner from the VH terminal, and outputs a complementary PWM signal to the PWM signal output from the VH terminal from the VL terminal. That is, in the period B, the V-phase coil 74 is alternately set to the first state and the second state. Note that the setting period from when the V-phase coil 74 is set to the first state to when it is set to the second state (first setting period) corresponds to the high-level period of the PWM signal output from the VH terminal. As shown in FIG. 6, this setting period increases with time in the period B, and then decreases. Note that in the period B, the microcomputer 51 outputs a low level from the UH terminal, and outputs a high level from the UL terminal (not shown). That is, in the period B, the U-phase coil 73 is set to the second state.

[0027] Furthermore, although not shown, in the B period, the microcomputer 51 outputs a low level from the WL terminal. Furthermore, as shown in FIG. 6, in the period B except for the C period, the microcomputer 51 outputs a low level from the WH terminal. In the C period (third period), the microcomputer 51 outputs a PWM signal whose duty changes in a sine wave shape from the WH terminal. In other words, in the period B except for the C period, the W-phase coil 75 is set to the third state, and in the C period, the W-phase coil 75 is alternately set to the first state and the third state. Note that in the C period, the setting period (second setting period) from when the W-phase coil 75 is set to the first state to when it is set to the third state corresponds to the high level period of the PWM signal output from the WH terminal. As shown in FIG. 6, this setting period increases with time in the C period, and then decreases.

[0028] In the period A, the coil current flows from the power supply terminal 66 through the U-phase high-side switching element, the U-phase coil 73, the V-phase coil 74, the V-phase low-side switching element, and the V-phase resistor 63 to the ground terminal 67. Note that a part of the coil current can also be supplied from the bulk electrolytic capacitor 65. As shown in FIG. 6, in the period A, the current value of the coil current increases with a delay from the increase in the duty of the PWM signal output from the UH terminal due to the inductance component of the coil. In a period different from the period C in the period B, the coil current flows from the ground terminal 67 through the U-phase resistor 63, the U-phase low-side switching element, the U-phase coil 73, the V-phase coil 74, and the V-phase high-side switching element to the power supply terminal 66. That is, the coil current flows as a regenerative current to a DC power supply (not shown) through the power supply terminal 66. Note that a part of the coil current flows not through the power supply terminal 66 but through the bulk electrolytic capacitor 65. In period C, the W-phase high-side switching element is turned ON, so part of the coil current flowing from V-phase coil 74 to the V-phase high-side switching element flows to W-phase coil 75 via the W-phase high-side switching element rather than through power supply terminal 66. The current flowing to W-phase coil 75 flows to V-phase coil 74 via neutral point 76. The coil current in Figure 6 indicates the current value (absolute value) of the current flowing toward inverter 60 in period A, and indicates the current value (absolute value) of the current flowing from inverter 60 to the power supply terminal in period B.

[0029] In this way, during period B for attenuating the coil current, part of the coil current is passed through the non-excited coil that is not included in the excitation phase, thereby reducing the current value of the regenerative current flowing into the DC power supply. Therefore, even if period B is shortened to hasten the attenuation of the coil current, the regenerative current to the DC power supply is prevented from increasing, and thus the power supply voltage is prevented from increasing. Therefore, by shortening period B, the time required to detect the rotor stop position can be shortened.

[0030] The length of time and maximum duty of period A are determined based on the required detection accuracy, provided that the rotor 72 does not rotate. In this example, the length of time and maximum duty of period A are set to 1 ms and 65%. The length of time and maximum duty of period B are set so that the increase in power supply voltage due to regenerative current is kept below a predetermined value, and the coil current is set to approximately zero at the end timing of period B. In order to make the coil current approximately zero at the end timing of period B, it is sufficient to set the time integral value of the voltage generated in the inductance component of the coil in period A to approximately zero. In this example, the length of period B is set to 1 ms, the same as period A, and the maximum duty is set to 24%.

[0031] The start timing of period C is set, for example, to a time period when the current value of the regenerative current is large. The length of time of period C and the maximum value of the duty are set so that the coil current flowing through the W-phase coil 75 decays to approximately zero within period B. In this example, the start timing of period C is set 0.25 ms after the start timing of period B, the length of time is set to 0.2 ms, and the maximum value of the duty is set to 70%. Note that the relationship between the elapsed time and the duty in period B can be adjusted by correcting the duty coefficient, which will be described later. The maximum value of the duty in period C is determined taking into consideration the adjustment of the duty in period B.

[0032] The change in the duty of the PWM signal applied to each coil, that is, the shape of the voltage waveform applied to the coil, may be a triangular wave or a trapezoidal wave, as shown in Fig. 7(A) and Fig. 7(B). More generally, the shape of the voltage waveform applied to the coil may increase toward a maximum value in each period, and decrease toward 0 when the maximum value is reached or at any timing thereafter. Furthermore, the change in the duty of the PWM signal applied to the coil may be a rectangular wave. In other words, the duty of the PWM signal applied to the coil may be constant in each period. Moreover, the shape of the change in the duty of the PWM signal in the A period, the B period, and the C period may not be the same.

[0033] In this embodiment, duty data is stored in advance in the non-volatile memory 55 of the microcomputer 51. Then, the microcomputer 51 outputs a PWM signal whose duty changes based on the duty data as shown in FIG. 6 and the like. FIG. 8 shows an example of duty data when the duty of the PWM signal is changed to a sine wave shape as shown in FIG. 6. The duty data is data that indicates the relationship between the elapsed time and the duty value in each period in a time series. #1 in FIG. 8 indicates the reference data for the A period and the B period, and #2 indicates the reference data for the C period. The non-volatile memory 55 also stores the duty coefficients for the A period, the B period, and the C period, and the microcomputer 51 obtains the actual duty value by multiplying the reference data by the duty coefficient. In this example, the duty coefficients for the A period, the B period, and the C period are 0.65, 0.24, and 0.7, respectively. Since the maximum value of the duty indicated by each reference data is 100, the maximum values ​​of the duty for the A period, the B period, and the C period are 65%, 24%, and 70%. Furthermore, the microcomputer 51 switches the duty cycle every 50 μs. Since the A and B periods are 1 ms, the reference data for #1 includes 20 time series values. Since the C period is 0.2 ms, the reference data for #2 includes 4 time series values.

[0034] The microcomputer 51 detects the current value of the coil current at a predetermined cycle in both the A period and the B period, and stores the detected current value as a measured value in the memory 57. As an example, the predetermined cycle may be 50 μs. When the B period ends, the microcomputer 51 determines the maximum value (absolute value) of the measured values ​​stored in the memory 57. As described above, the microcomputer 51 excites each of the six excitation phases and determines the maximum value for each excitation phase. FIG. 9 shows an example of the maximum value determined for the six excitation phases. According to FIG. 9, the maximum value is the largest when the UV phase is excited. As described above, when the rotor 72 is stopped at the XY phase position, the synthetic impedance measured when the XY phase is excited is the smallest, and therefore the current value of the coil current measured when the XY phase is excited is the largest. Therefore, in the case of FIG. 9, it can be determined that the stop position of the rotor 72 is the UV phase position.

[0035] Next, a method of correcting the duty factor will be described. The duty factor is initially determined in advance according to the standard parameters of the motor 15F so that the coil current at the end timing of the B period approaches 0. However, due to variations in the characteristics of the individual motors 15F, the optimal duty factor may differ for each individual motor 15F. Furthermore, due to changes over time in the motor 15F, the optimal duty factor may change over time. For this reason, in this embodiment, the duty factor is updated and corrected when a predetermined condition is satisfied. The predetermined condition may be configured to be satisfied, for example, when the image forming apparatus is turned on or when the image forming apparatus returns from a sleep state. In addition, the predetermined condition may be a periodic condition or a condition based on the number of sheets on which an image is formed. Furthermore, the predetermined condition may be configured to be satisfied when the current value (absolute value) of the coil current at the end timing of the B period is greater than a predetermined value. In this embodiment, three different duty factors are used for each of the A period, the B period, and the C period, but only one duty factor is updated. In this embodiment, the duty factor for period B is updated, but the duty factor for periods A and C may also be updated. The duty factor is updated so that the current value of the coil current at the end timing of period B approaches 0. In the following description, the current value of the coil current at the end timing of period B is referred to as the "final value."

[0036] For example, if the final value is a negative value, that is, in XY phase excitation, when the coil current flows from the Y phase coil to the X phase coil at the end timing of period B, the duty of period B is too large. Therefore, in such a case, the duty factor is updated to be smaller than the current value. On the other hand, if the final value is a positive value, that is, in XY phase excitation, when the coil current flows from the X phase coil to the Y phase coil, the duty of period B is too small, so the duty factor is updated to be larger than the current value.

[0037] FIG. 10 is a flowchart of the rotor stop position detection process executed by the motor control unit 14. In S10, the motor control unit 14 selects an excitation phase to be excited. In S11, the motor control unit 14 executes a measurement process for the excitation phase selected in S10. That is, the motor control unit 14 outputs a PWM signal based on the duty data and the duty coefficient as described in FIG. 6 and FIG. 7, and repeatedly measures the current value of the coil current. The motor control unit 14 stores the repeatedly measured current value as a measured value in the memory 57. When the B period is completed, the motor control unit 14 determines the maximum value of the repeatedly measured current value in S12. In S13, the motor control unit 14 waits until the current value (absolute value) of the coil current becomes equal to or less than a threshold value. When the current value of the coil current becomes equal to or less than the threshold value, the motor control unit 14 determines in S14 whether or not measurements have been performed for all six excitation phases, and if not, repeats the process from S10. On the other hand, when the measurements have been completed for all of the six excitation phases, in S15, the motor control unit 14 determines the stop position of the rotor 72 based on the maximum value of the coil current measured for each excitation phase.

[0038] The process in Fig. 10 is an example, and the rotor stop position detection process in this embodiment is not limited to following the flowchart shown in Fig. 10. For example, the determination of the maximum value of the excitation phase (S12) can be performed after the measurement of all excitation phases is completed. Also, when the B period for the excitation of a certain excitation phase is completed, the determination in S14 is performed, and if the determination in S14 is No, the process may be configured to wait (S13) until the coil current reaches a threshold value, and then repeat the process from S10.

[0039] FIG. 11 is a flowchart of the duty coefficient update process executed by the motor control unit 14. The process in FIG. 11 is related to the update of the duty coefficient for one excitation phase, and the motor control unit 14 repeats the process in FIG. 11 for six excitation phases. In S20, the motor control unit 14 outputs a PWM signal based on the duty data and the duty coefficient as described in FIG. 6 and FIG. 7. The duty coefficient used in S20 uses the value at that time. In S21, which is the end timing of the B period, the motor control unit 14 stores the final value of the coil current in the memory 57 as a first judgment value. In S22, the motor control unit 14 waits until the current value (absolute value) of the coil current becomes equal to or less than the threshold value.

[0040] When the current value (absolute value) of the coil current becomes equal to or less than the threshold value, the motor control unit 14 outputs a PWM signal as described in FIG. 6 and FIG. 7 based on the duty data and the first modified duty coefficient in S23. The first modified duty coefficient is a value obtained by modifying the duty coefficient of the B period to be updated among the current duty coefficients of the A period, the B period, and the C period to a value smaller than the current value. As an example, the motor control unit 14 modifies the duty coefficient of the B period by multiplying the current duty coefficient of the B period by an adjustment value smaller than 1, for example, 0.95. In S24, which is the end timing of the B period, the motor control unit 14 stores the final value of the coil current in the memory 57 as a second judgment value. In S25, the motor control unit 14 waits until the current value (absolute value) of the coil current becomes equal to or less than the threshold value.

[0041] When the current value (absolute value) of the coil current becomes equal to or lower than the threshold value, in S26, the motor control unit 14 outputs a PWM signal based on the duty data and the second modified duty coefficient as described in FIG. 6 and FIG. 7. The second modified duty coefficient is a modified duty coefficient of the B period to be updated among the current duty coefficients of the A period, the B period, and the C period, to a value larger than the current value. As an example, the motor control unit 14 modifies the duty coefficient of the B period by multiplying the current duty coefficient of the B period by an adjustment value larger than 1, for example, 1.05. In S27, which is the end timing of the B period, the motor control unit 14 stores the final value of the coil current in the memory 57 as a third judgment value.

[0042] Thereafter, in S28, the motor control unit 14 updates the duty coefficient of the B period based on the first to third judgment values ​​so that the coil current approaches 0 at the end timing of the B period. As an example, the motor control unit 14 obtains a relationship between the value of the duty coefficient of the B period and the final value based on the value of the duty coefficient of the B period used in S20, S23, and S26 and the first to third judgment values. The relationship between the value of the duty coefficient of the B period and the final value can be obtained, for example, by linear interpolation of the three judgment values. Then, based on the obtained relationship, the motor control unit 14 obtains a duty coefficient value that makes the current value of the coil current at the end timing of the B period 0, and stores this in the non-volatile memory 55 as the value of the duty coefficient of the B period after update.

[0043] Note that the duty coefficient update process in Fig. 11 can be performed as a process independent of the rotor stop position detection process in Fig. 10, but the first judgment value in S21 in Fig. 11 can be obtained in the rotor stop position detection process in Fig. 10. That is, the coil current value measured at the end timing of period B in S11 in Fig. 10 can be used as the first judgment value. In this case, only the process from S23 onwards is executed for the duty coefficient update process in Fig. 11, and the value judged in the latest rotor stop position detection process is used as the first judgment value.

[0044] As described above, according to this embodiment, a part of the regenerative current is consumed by passing it through the non-excitation coil. With this configuration, even if the inverter 60 is controlled to hasten the decay time of the coil current, it is possible to suppress an increase in the power supply voltage. Therefore, by controlling to hasten the decay time of the coil current, the time required for the measurement process of each excitation phase is shortened, and thus the time required for detecting the rotor stop position can be shortened.

[0045] Second Embodiment Next, the second embodiment will be described focusing on the differences from the first embodiment. In this embodiment, the change in the duty of the PWM signal over time is different from that in the first embodiment. Fig. 12 shows the change in the duty of the PWM signal output from the PWM port 58 over time in the measurement process of the UV phase in this embodiment. The period A is the same as in the first embodiment.

[0046] In this embodiment, the B period is set to 0.5 ms, and the duty of the PWM signal output from the VH terminal is changed in an M-shape as shown in FIG. 12. That is, when the B period starts, the first set period during which the V-phase coil 74 is set from the first state to the second state is set to a maximum value, and then the first set period is shortened as time passes. Then, from a certain timing to the completion of the B period, the first set period is increased as time passes. The timing at which the first set period is changed from a decrease to an increase can be, for example, the timing at which half the period of the B period has elapsed from the start of the B period. By controlling in this manner, the regenerative current flowing out from the second terminal of the V-phase coil 74 through the switching element on the V-phase high side increases from the start of the B period, and therefore the voltage of the bulk electrolytic capacitor 65 can be quickly increased. Then, the first set period is shortened as the voltage of the bulk electrolytic capacitor 65 increases, so that the regenerative current to the DC power source does not increase. Furthermore, the duty is increased as the coil current decreases. With this configuration, it is possible to reduce the change over time in the regenerative current flowing into the DC power supply during period B, and therefore it is possible to suppress the voltage rise of the DC power supply.

[0047] In addition, in period C, the time change in the duty of the PWM signal output from the WH terminal is set so that the coil current flowing through the W-phase coil 75 decays to 0 within period B. In this example, as shown in FIG. 12, period C is set to a 0.1 ms period starting simultaneously with period B, and the duty of the PWM signal output from the WH terminal is changed to a rectangular wave. In other words, in period C, the second setting period from when the W-phase coil 75 is set to the first state to when it is set to the third state is kept constant. #1, #2, and #3 in FIG. 13 indicate duty data in periods A, B, and C, respectively.

[0048] As described above, in this embodiment, it is possible to reduce the time change of the regenerative current in period B, and therefore to suppress the voltage rise of the DC power supply. Therefore, the decay time of the coil current is controlled to be accelerated, thereby shortening the time required for the measurement process of each excitation phase, and thus shortening the time required for detecting the rotor stop position.

[0049] [Other embodiments] The motor control unit 14 can be implemented as a motor control device. The motor control unit 14 and the printer control unit 11 can be implemented as a motor control device. In the above embodiment, the control of the motor 15F that drives the fixing unit 24 is described as an example, but the present invention can be similarly applied to a motor that drives any rotating member of the image forming device. The rotating members of the image forming device are, for example, each roller related to the transport of a sheet, a photoconductor in the image forming unit 1, a developing roller, etc. Furthermore, each of the above embodiments can be applied to a motor in which the first terminals of three or more coils are connected to each other. In addition, the number of magnetic poles of the roller is not limited to two, and each of the above embodiments can be applied to the control of a motor with any number of poles.

[0050] 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.

[0051] The disclosure of this embodiment includes the following configuration. (Configuration 1) An image forming apparatus for forming an image on a sheet conveyed through a conveying path, A rotating member; a motor for driving the rotating member, the motor having at least three coils, first terminals of the at least three coils being interconnected; and a motor control means for controlling the motor by controlling a potential of a second terminal different from the first terminal of the at least three coils, the motor control means performing a measurement process for controlling a coil current to flow from a first coil to a second coil of the at least three coils and measuring a current value of the coil current for each of a plurality of excitation phases specified by a permutation of two coils of the at least three coils, thereby detecting a stop position of a rotor of the motor; Equipped with an image forming apparatus, wherein the motor control means controls the coil current to flow from the first coil to the second coil during a first period of the measurement process, controls the coil current that flowed from the first coil to the second coil during the first period to be attenuated during a second period following the first period, and controls the coil current that flowed from the first coil to the second coil during a third period within the second period to flow from the second terminal of the second coil to the third coil via the second terminal of a third coil different from the first coil and the second coil among the at least three coils. (Configuration 2) The motor control means controls each of the at least three coils to a first state in which the second terminal of the coil is connected to a third terminal at a first potential; a second state in which the second terminal of the coil is connected to a fourth terminal at a second potential lower than the first potential; a third state in which the second terminal of the coil is not connected to either the third terminal or the fourth terminal; and controlling the motor by setting the motor to one of the following: The motor control means During the second period, the first coil is set to the second state, and the second coil is alternately set to the first state and the second state; setting the third coil to the third state during a period of the second period that is different from the third period; 2. The image forming apparatus according to claim 1, wherein the third coil is alternately set to the first state and the third state during the third period. (Configuration 3) The image forming apparatus according to configuration 2, wherein the motor control means controls the second coil so that, during the second period, a first setting period from when the second coil is set to the first state to when the second coil is set to the second state becomes larger over time, and thereafter, the first setting period becomes smaller over time. (Configuration 4) The image forming apparatus according to configuration 2 or 3, wherein the motor control means controls the motor so that, during the third period, a second setting period from when the third coil is set to the first state to when the third coil is set to the third state becomes larger over time, and thereafter, the second setting period becomes smaller over time. (Configuration 5) The image forming apparatus according to configuration 2, wherein the motor control means controls the second coil so that, during the second period, a first setting period from when the second coil is set to the first state to when the second coil is set to the second state becomes shorter over time, and thereafter, the first setting period becomes longer over time. (Configuration 6) The image forming apparatus according to configuration 2 or 5, wherein the motor control means controls the third coil so that a second setting period from when the third coil is set to the first state to when the third coil is set to the third state is constant during the third period. (Configuration 7) The image forming apparatus of any one of configurations 3 to 6, wherein the motor control means has data indicating a relationship between elapsed time and a set period, determines the relationship between the elapsed time in the second period and the first set period by multiplying the set period indicated by the data by a coefficient, determines a current value of the coil current flowing from the first coil to the second coil at an end timing of the second period, and updates the coefficient so that the current value of the coil current flowing from the first coil to the second coil approaches 0 at the end timing of the second period. (Configuration 8) The image forming apparatus of configuration 7, wherein the motor control means updates the coefficient to be larger if the current value of the coil current flowing from the first coil to the second coil at the end timing of the second period is a positive value, and updates the coefficient to be smaller if the current value of the coil current flowing from the first coil to the second coil at the end timing of the second period is a negative value. (Configuration 9) The motor control means 9. The image forming apparatus of any one of configurations 2 to 8, wherein, during the first period, the second coil is set to the second state, the third coil is set to the third state, and the first coil is alternately set to the first state and the second state. (Configuration 10) The image forming apparatus of configuration 9, wherein the motor control means controls the motor so that, during the first period, a third setting period from when the first coil is set to the first state to when the first coil is set to the second state becomes larger over time, and thereafter, the third setting period becomes smaller over time. (Configuration 11) The image forming apparatus according to any one of configurations 1 to 10, wherein the motor control means determines a maximum value of the coil current flowing from the first coil to the second coil in the measurement process, and detects a stop position of the rotor based on the maximum value determined in the measurement process performed for each of the multiple excitation phases. (Configuration 12) 12. The image forming apparatus according to claim 11, wherein the motor control means detects a stop position of the rotor based on a maximum value among the maximum values ​​determined in the measurement process performed for each of the plurality of excitation phases.

[0052] 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]

[0053] 15F: Motor, 60: Inverter, 51: Microcomputer

Claims

1. An image forming apparatus for forming an image on a sheet conveyed through a conveying path, A rotating member; a motor for driving the rotating member, the motor having at least three coils, first terminals of the at least three coils being interconnected; and a motor control means for controlling the motor by controlling a potential of a second terminal different from the first terminal of the at least three coils, the motor control means performing a measurement process for controlling a coil current to flow from a first coil to a second coil of the at least three coils and measuring a current value of the coil current for each of a plurality of excitation phases specified by a permutation of two coils of the at least three coils, thereby detecting a stop position of a rotor of the motor; Equipped with An image forming apparatus, wherein the motor control means controls the coil current to flow from the first coil to the second coil during a first period of the measurement process, controls the coil current that flowed from the first coil to the second coil during the first period to be attenuated during a second period following the first period, and controls the coil current that flowed from the first coil to the second coil during a third period within the second period to flow from the second terminal of the second coil to the third coil via the second terminal of a third coil different from the first coil and the second coil among the at least three coils.

2. The motor control means controls each of the at least three coils to a first state in which the second terminal of the coil is connected to a third terminal at a first potential; a second state in which the second terminal of the coil is connected to a fourth terminal at a second potential lower than the first potential; a third state in which the second terminal of the coil is not connected to either the third terminal or the fourth terminal; and controlling the motor by setting the motor to one of the following: The motor control means During the second period, the first coil is set to the second state, and the second coil is alternately set to the first state and the second state; setting the third coil to the third state during a period of the second period that is different from the third period; The image forming apparatus according to claim 1 , wherein the third coil is alternately set to the first state and the third state during the third period.

3. 3. The image forming apparatus according to claim 2, wherein the motor control means controls the second coil so that, during the second period, a first set period from when the second coil is set to the first state to when the second coil is set to the second state becomes larger over time, and thereafter, the first set period becomes smaller over time.

4. 3. The image forming apparatus according to claim 2, wherein the motor control means controls the motor so that, during the third period, a second setting period from when the third coil is set to the first state to when the third coil is set to the third state becomes larger over time, and thereafter, the second setting period becomes smaller over time.

5. 3. The image forming apparatus according to claim 2, wherein the motor control means controls the second coil so that, during the second period, a first set period from when the second coil is set to the first state to when the second coil is set to the second state becomes shorter over time, and thereafter, the first set period becomes longer over time.

6. 3. The image forming apparatus according to claim 2, wherein the motor control means controls the third coil so that a second set period from when the third coil is set to the first state until when the third coil is set to the third state is constant during the third period.

7. The image forming apparatus of claim 3 or 5, wherein the motor control means has data indicating the relationship between elapsed time and a set period, determines the relationship between the elapsed time in the second period and the first set period by multiplying the set period indicated by the data by a coefficient, determines the current value of the coil current flowing from the first coil to the second coil at the end timing of the second period, and updates the coefficient so that the current value of the coil current flowing from the first coil to the second coil approaches zero at the end timing of the second period.

8. 8. The image forming apparatus of claim 7, wherein the motor control means updates the coefficient to be larger when the current value of the coil current flowing from the first coil to the second coil at the end timing of the second period is a positive value, and updates the coefficient to be smaller when the current value of the coil current flowing from the first coil to the second coil at the end timing of the second period is a negative value.

9. The motor control means 3. The image forming apparatus according to claim 2, wherein, during the first period, the second coil is set to the second state, the third coil is set to the third state, and the first coil is alternately set to the first state and the second state.

10. 10. The image forming apparatus according to claim 9, wherein the motor control means controls the motor so that, during the first period, a third set period from when the first coil is set to the first state to when the first coil is set to the second state becomes larger over time, and thereafter, the third set period becomes smaller over time.

11. 3. The image forming apparatus according to claim 1, wherein the motor control means determines a maximum value of the coil current flowing from the first coil to the second coil in the measurement process, and detects a stop position of the rotor based on the maximum value determined in the measurement process performed for each of the multiple excitation phases.

12. 12. The image forming apparatus according to claim 11, wherein the motor control means detects the stop position of the rotor based on the maximum value among the maximum values ​​determined in the measurement process performed for each of the plurality of excitation phases.

Images