Image forming device

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, which 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. To prevent loss of synchronism or reverse rotation during startup, the sensorless DC brushless motor detects the rotor stop position (hereinafter referred to as the 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) flows through each of a plurality of excitation phases of the 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] Japanese Patent Application Laid-Open No. 2015-104263 Summary of the Invention [Problem to be solved by the invention]

[0004] In an image forming apparatus, the time required for printing can be reduced by shortening the motor startup time. An effective way to shorten the motor startup time is to shorten the time required to detect the rotor stop position. To detect the rotor stop position, it is necessary to pass a coil current through each of multiple excitation phases and measure the current value. However, measurement for a given excitation phase cannot begin 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 given excitation phase.

[0005] However, if the coil current decay rate is increased, the regenerative current to the power supply increases, which can cause the power supply voltage to rise. While it is possible to reduce the regenerative current by increasing the capacity of the electrolytic capacitor connected to the power supply line, this increases costs and the size of the image forming apparatus.

[0006] The present invention provides a technique that can reduce 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 on a conveying path includes a rotating member, a motor for driving the rotating member, the motor having at least three coils, each of the at least three coils having a first terminal and a second terminal, the first terminals of the at least three coils being connected to each other, and a motor control unit for controlling the motor by controlling the potentials of the second terminals of the at least three coils, the motor control unit controlling the motor by controlling the potentials of the second terminals of the at least three coils, the motor control unit controlling the motor by controlling the potentials of the second terminals of the at least three coils, the motor control unit controlling the coil current so that a coil current flows from a first coil to a second coil of the at least three coils, and measuring a current value of the coil current, the motor control unit controlling the coil current so that a coil current flows from a first coil to a second coil of the at least three coils, the motor control unit controlling the motor by controlling the potentials of the second terminals of the at least three coils ... motor by controlling the potentials of the second terminals of the at least three coils, the motor control unit controlling the coil current so that a coil current flows from a first coil to a second coil of the at least three coils, and measuring a current value of the coil current, the motor control unit controlling the motor by controlling the potentials of the second terminals of the at least three coils, the motor control unit controlling the motor by controlling the potentials of the second terminals of the at least three coils, the motor control unit controlling the motor by controlling the potentials of the second terminals of the at least three coils, the motor control unit controlling the motor by controlling the potentials of the second terminals of the at least three coils, the motor control unit controlling the motor by controlling the potentials of the second terminals of the at least three coils, the motor control unit controlling the potentials of the second and the motor control means detects a stop position of the rotor of the motor by performing a measurement on the first coil to detect a stop position of the rotor of the 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 to attenuate during a second period following the first period, and controls the coil current to attenuate during a third period within the second period so that a part of the coil current flowing from the first coil to the second coil flows from the second terminal of the second coil to the third coil, the third coil being different from the first coil and the second coil, among the at least three coils. the motor control means controls the motor by setting each of the at least three coils to one of 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, and a third state in which the second terminal of the coil is not connected to either the third terminal or the fourth terminal, and the motor control means sets the first coil to the second state and alternately sets the second coil to the first state and the second state during the second period, sets the third coil to the third state during a period different from the third period within the second period, and alternately sets the third coil to the first state and the third state during the third period. do. [Effects of the Invention]

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

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

[0010] Hereinafter, embodiments will be described in detail with reference to the accompanying drawings. Note that the following embodiments do not limit the scope of the invention claimed. Although multiple features are described in the embodiments, not all of these multiple features are necessarily essential to the invention, and multiple features may be combined arbitrarily. Furthermore, in the accompanying drawings, the same reference numerals are used to designate the same or similar components, and redundant explanations will be omitted.

[0011] First Embodiment FIG. 1 is a structural diagram of an image forming apparatus according to this embodiment. The image forming apparatus may be, for example, a printing apparatus, printer, copier, multifunction peripheral, or facsimile machine. Sheets stored in a cassette 25 of the image forming apparatus are transported along a transport path by a feed roller 26 and a transport roller 27. An image forming unit 1 forms yellow, magenta, cyan, and black toner images and transfers them to a sheet transported along the transport path. A fuser 24 has a heating roller and a pressure roller, and heats and presses the sheet to which the toner image has been transferred, fixing the toner image to the sheet. The sheet with the fixed toner image is discharged outside the image forming apparatus. A motor 15F is a drive source that rotates the rollers of the fuser 24. The motor 15F may be a sensorless motor that does not include a sensor for detecting the rotor position. While the image forming apparatus shown in FIG. 1 is a color image forming apparatus that forms images using four color toners, the image forming apparatus may also be a monochrome image forming apparatus that forms images using only black toner, for example. Furthermore, although the image forming apparatus in FIG. 1 is an electrophotographic image forming apparatus, the image forming apparatus may be an inkjet image forming apparatus 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 for 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 fuser 24 to fuse the toner image to the sheet. At this time, the printer control unit 11 also controls the motor control unit 14 to control the rotation of each motor 15, including the motor 15F. The motor 15 is a driving source for, for example, the rollers of the fuser 24, the rollers of the conveyance unit that conveys the sheet along the conveyance path, and the rotating members included in the image forming unit 1. The conveyance unit includes, for example, a feed roller 26 and a conveyance roller 27. The rotating members of the image forming unit 1 include, for example, a photosensitive element and a developing roller. The printer control unit 11 also displays the status 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 part of the image forming apparatus based on the various control programs and data stored in the memory.

[0013] FIG. 3 shows an example configuration of the motor control unit 14. The motor control unit 14 has a microcomputer (hereinafter referred to as "mc") 51. The mc 51 communicates with the printer control unit 11 via a communication port 52. The mc 51 outputs pulse width modulation signals (PWM signals) from a PWM port 58. In this embodiment, the mc 51 outputs 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. Therefore, the PWM port 58 has six terminals: UH, VH, WH, UL, VL, and WL. Each terminal of the PWM port 58 is connected to a gate driver 61.

[0014] The inverter 60 has six switching elements, each corresponding to a PWM signal output from the PWM port 58. That is, the inverter 60 has a switching element corresponding to each of the UH, VH, WH, UL, VL, and WL signals. The switching elements may be, for example, FETs. The gate driver 61 controls the ON / OFF 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 of the coils 73, 74, and 75, which are different from the second terminals, 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 coil 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 are input to the AD converter 53 of the microcomputer 51 via 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 values ​​of the coil currents flowing through the coils 73, 74, and 75 based on the digital value. In this way, the resistors 63, amplifier 64, and microcomputer 51 constitute a current detection unit that detects the current values ​​of the coil currents. The microcomputer 51 also has a nonvolatile memory 55 that stores various data used to control the motor 15F, and a volatile memory 57.

[0018] Each of the coils 73, 74, and 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. In the first state, only the high-side switching element corresponding to the coil is turned on, thereby connecting the second terminal of the coil to the power supply terminal 66 at a first potential (e.g., +24 V). In the second state, only the low-side switching element corresponding to the coil is turned on, thereby connecting the second terminal of the coil via the resistor 63 to the ground terminal 67 at a second potential (e.g., ground potential) lower than the first potential. In the third state, both the high-side and low-side switching elements corresponding to the coil are turned off, thereby disconnecting the second terminal of the coil from both the power supply terminal 66 and the ground terminal 67, i.e., 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 illustrates an exemplary configuration of a motor 15F. The motor 15F includes a six-slot stator 71 and a four-pole rotor 72. The stator 71 includes a U-phase coil 73, a V-phase coil 74, and a W-phase coil 75. The rotor 72 is configured with a permanent magnet and includes two pairs of north and south poles. The rotor 72 stops at a position determined by the excitation phase. In this embodiment, the excitation phase is determined by the order of two of the coils 73, 74, and 75. That is, there are six excitation phases: UV, UW, VU, VW, WU, and WV. Exciting the UV phase here means exciting the rotor 72 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 rotational position shown in FIG. 4(A). At this time, the U phase becomes the N pole and the V phase becomes the 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 motor 15F is stopped and the coil current is set to 0, the force holding rotor 72 ceases to act, and rotor 72 will rotate if an external rotational force is applied to rotor 72. Therefore, rotor 72 can rotate when fixing unit 24 is removed from the image forming apparatus, or when a sheet caught in fixing unit 24 due to a jam is removed. At this time, motor control unit 14 is unable to determine the stopping position of rotor 72. Furthermore, even immediately after powering on the image forming apparatus, motor control unit 14 is unable to determine the stopping position of rotor 72. Therefore, when motor control unit 14 rotates motor 15F, it first performs a process to detect the stopping position of rotor 72.

[0021] Generally, coils such as coils 73, 74, and 75 are constructed by winding copper wire around a core made of laminated electromagnetic steel sheets. The magnetic permeability of electromagnetic steel sheets decreases in the presence of an external magnetic field. Because the inductance of a coil is proportional to the magnetic permeability of the core, a decrease in the magnetic permeability of the core also decreases the inductance of the coil. For example, in FIG. 4A, the U-phase coil 73 faces only the south pole of the rotor 72, so its inductance decreases more than that of the W-phase coil 75, which faces both the south and north poles of the rotor 72. Furthermore, the amount of change in inductance depends 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 shown in FIG. 4A, if a coil current is passed through the U-phase coil 73 in the same direction as the magnetic field generated by the opposing south pole of the rotor 72, i.e., so that the U-phase becomes the north pole, the amount of inductance decrease is greater than if a coil current is passed through the U-phase coil 73 in the direction so that the U-phase becomes the south pole. In this way, the detected inductance value differs depending on the stop position of the rotor 72 and the excitation phase. Furthermore, 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 if the UV phase is excited. Hereinafter, the position where the rotor 72 stops when the XY phase is excited will be referred to as the "XY phase position." Because the rotor 72 is stopped at the UV phase position, the composite impedance when the UV phase is excited is smaller than the composite impedance when the other excitation phases are excited. Therefore, the position of the rotor 72 can be determined by determining the relative magnitude relationship of the composite impedance of each excitation phase. In this embodiment, as described below, a measurement process in which the excitation phase is excited and the coil current is measured is performed sequentially for each excitation phase. 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 following describes the measurement process for the UV phase as a representative example. The U-phase coil 73 (first coil) and the V-phase coil 74 (second coil), which are the excitation targets in the UV-phase measurement process, are hereinafter referred to as "excitation coils," and the W-phase coil 75 (third coil), which is not included in the excitation phases, is hereinafter referred to as "non-excitation coil." As shown in FIG. 6 , the measurement process period 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 during which the inverter 60 is controlled to flow a coil current from the U-phase coil 73 to the V-phase coil 74. Meanwhile, period B is a period during which the inverter 60 is controlled to attenuate the coil current that flowed from the U-phase coil 73 to the V-phase coil 74 during period A. 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. During the period A, the microcomputer 51 outputs a PWM signal from the UH terminal, whose high-level duty cycle varies sinusoidally. Although not shown, the microcomputer 51 also outputs a PWM signal (hereinafter referred to as a complementary PWM signal) from the UL terminal, whose polarity is inverted from the PWM signal output from the UH terminal. Therefore, during the period A, the second terminal of the U-phase coil 73 is connected to the power supply terminal 66 while the PWM signal output from the UH terminal is high, and is connected to the ground terminal 67 via the resistor 63 while the PWM signal is low. That is, during the period A, the U-phase coil 73 is alternately set to the first state and the second state. Note that the setting period from when the U-phase coil 73 is set to the first state until when it is set to the second state (third setting period) corresponds to the high-level period of the PWM signal output from the UH terminal. As shown in FIG. 6, this setting period increases over time during the period A and then decreases.

[0025] Furthermore, during period A, microcomputer 51 outputs a low level (duty is 0%) from the VH terminal and the WH terminal. Although not shown, during 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, during period A, V-phase coil 74 is set to the second state, and W-phase coil 75 is set to the third state.

[0026] During period B (second period) following period A, the microcomputer 51 outputs a high-level PWM signal with a sinusoidally varying duty cycle 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, during period B, the V-phase coil 74 is alternately set to the first state and the second state. The setting period (first setting period) from when the V-phase coil 74 is set to the first state until when it is set to the second state corresponds to the high-level period of the PWM signal output from the VH terminal. As shown in FIG. 6, this setting period increases over time during period B and then decreases. During period B, the microcomputer 51 outputs a low level from the UH terminal and a high level (not shown) from the UL terminal. That is, during period B, the U-phase coil 73 is set to the second state.

[0027] Furthermore, although not shown, during period B, the microcomputer 51 outputs a low level from the WL terminal. Furthermore, as shown in FIG. 6, during period B except period C, the microcomputer 51 outputs a low level from the WH terminal. During period C (third period), the microcomputer 51 outputs a PWM signal from the WH terminal, the duty of which varies sinusoidally. In other words, during period B except period C, the W-phase coil 75 is set to the third state, and during period C, the W-phase coil 75 is alternately set to the first state and the third state. Note that during period C, 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 over time during period C, and then decreases.

[0028] During 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 portion of the coil current can also be supplied from the bulk electrolytic capacitor 65. As shown in FIG. 6 , during Period A, the current value of the coil current increases with a delay relative to the increase in the duty cycle of the PWM signal output from the UH terminal due to the coil inductance component. During a period different from Period C within 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. In other words, the coil current flows as a regenerative current to a DC power supply (not shown) via the power supply terminal 66. Note that a portion of the coil current flows not through the power supply terminal 66 but through the bulk electrolytic capacitor 65. During 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 during period A, and indicates the current value (absolute value) of the current flowing from inverter 60 to the power supply terminal during period B.

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

[0030] The length of period A and the maximum duty are determined based on the required detection accuracy, provided that the rotor 72 does not rotate. In this example, the length of period A and the maximum duty are set to 1 ms and 65%, respectively. The length of period B and the maximum duty are set so that the increase in power supply voltage due to regenerative current is kept below a predetermined value, while the coil current is set to approximately zero at the end of period B. Note that, to make the coil current approximately zero at the end of period B, the time integral of the voltage generated in the coil's inductance component during period A can be set 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 duration 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 duration 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 account the adjustment of the duty in period B.

[0032] The change in duty of the PWM signal applied to each coil, i.e., the shape of the voltage waveform applied to the coil, may be triangular or trapezoidal, as shown in Figures 7(A) and 7(B). More generally, the shape of the voltage waveform applied to the coil can be such that it increases toward a maximum value in each period and decreases toward zero when it reaches the maximum value or at any time thereafter. Furthermore, the change in duty of the PWM signal applied to the coil can also be a square wave. In other words, the duty of the PWM signal applied to the coil can be constant in each period. Furthermore, the shape of the change in duty of the PWM signal in periods A, B, and C does not have to be the same.

[0033] In this embodiment, duty data is stored in advance in the nonvolatile memory 55 of the microcomputer 51. The microcomputer 51 then outputs a PWM signal whose duty varies based on the duty data, as shown in FIG. 6 and other figures. FIG. 8 shows an example of duty data when the duty of the PWM signal varies sinusoidally 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 reference data for periods A and B, and #2 indicates reference data for period C. The nonvolatile memory 55 also stores duty coefficients for periods A, B, and C, respectively. The microcomputer 51 calculates the actual duty value by multiplying the reference data by the duty coefficient. In this example, the duty coefficients for periods A, B, and C are 0.65, 0.24, and 0.7, respectively. Since the maximum duty indicated by each reference data is 100, the maximum duty values ​​for periods A, B, and C are 65%, 24%, and 70%, respectively. Furthermore, the microcomputer 51 switches the duty cycle every 50 μs. Since periods A and B are 1 ms each, the reference data for #1 includes 20 time series values. Since period C is 0.2 ms, the reference data for #2 includes 4 time series values.

[0034] The microcomputer 51 detects the coil current value at a predetermined cycle during both Period A and Period B and stores the detected current value in the memory 57 as a measured value. For example, the predetermined cycle may be 50 μs. When Period B 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. Figure 9 shows an example of the maximum values ​​determined for the six excitation phases. According to Figure 9, the maximum value is greatest when the UV phase is excited. As described above, when the rotor 72 is stopped at the XY phase position, the composite impedance measured when the XY phase is excited is smallest, and therefore the current value of the coil current measured when the XY phase is excited is largest. Therefore, in the case of Figure 9, it can be determined that the rotor 72 is stopped at the UV phase position.

[0035] Next, a method for correcting the duty factor will be described. The duty factor is initially determined in advance based on the standard parameters of the motor 15F so that the coil current approaches zero at the end of period B. However, due to variations in the characteristics of individual motors 15F, the optimal duty factor may differ for each individual motor 15F. Furthermore, the optimal duty factor may change over time due to aging of the motor 15F. For this reason, in this embodiment, the duty factor is updated and corrected when a predetermined condition is met. The predetermined condition may be met, for example, when the image forming apparatus is turned on or when the apparatus returns from a sleep state. The predetermined condition may also be a periodic condition or a condition based on the number of sheets on which images have been formed. Furthermore, the predetermined condition may also be met when the current value (absolute value) of the coil current at the end of period B is greater than a predetermined value. In this embodiment, three different duty factors are used for periods A, B, and C, but only one duty factor is updated. In this embodiment, the duty coefficient for period B is updated, but the duty coefficient for periods A and C may also be updated. The duty coefficient is updated so that the current value of the coil current at the end timing of period B approaches 0. In the following explanation, 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 of period B, the duty for period B is too large. Therefore, in such a case, the duty coefficient 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 for period B is too small, so the duty coefficient 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 measurement processing for the excitation phase selected in S10. That is, the motor control unit 14 outputs a PWM signal based on the duty data and duty coefficient as described with reference to FIGS. 6 and 7, and repeatedly measures the current value of the coil current. The motor control unit 14 stores the repeatedly measured current value as a measurement 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 measurements have been performed for all six excitation phases. If measurements have not been performed, the motor control unit 14 repeats the process from S10. On the other hand, if measurements have been completed for all six excitation phases, the motor control unit 14 determines the stop position of the rotor 72 in S15 based on the maximum value of the coil current measured for each excitation phase.

[0038] 10 is merely 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 measurements of all excitation phases have been completed. Alternatively, when period B for excitation of a certain excitation phase is completed, the determination of S14 may be performed, and if the determination of S14 is No, the process may wait (S13) until the coil current reaches a threshold value, and repeat the process from S10.

[0039] FIG. 11 is a flowchart of the duty coefficient update process executed by the motor control unit 14. Note that the process in FIG. 11 relates to updating 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 duty coefficient as described in FIGS. 6 and 7. Note that the duty coefficient used in S20 uses the value at that time. In S21, which is the end timing of period B, the motor control unit 14 stores the final value of the coil current in 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 a 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 in S23 based on the duty data and the first modified duty coefficient, as described with reference to FIGS. 6 and 7. The first modified duty coefficient is obtained by modifying the duty coefficient of period B, which is the current duty coefficient to be updated among the current duty coefficients of periods A, B, and C, to a value smaller than the current value. As an example, the motor control unit 14 modifies the duty coefficient of period B by multiplying the current duty coefficient of period B by an adjustment value smaller than 1, for example, 0.95. In S24, which is the end timing of period B, the motor control unit 14 stores the final value of the coil current in memory 57 as a second determination 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 falls below the threshold, in S26, the motor control unit 14 outputs a PWM signal based on the duty data and the second modified duty coefficient, as described with reference to FIGS. 6 and 7. The second modified duty coefficient is obtained by modifying the duty coefficient of period B, which is the current duty coefficient for period A, period B, and period C to a value greater than the current value. As an example, the motor control unit 14 modifies the duty coefficient of period B by multiplying the current duty coefficient of period B by an adjustment value greater than 1, for example, 1.05. In S27, which is the end timing of period B, the motor control unit 14 stores the final value of the coil current in memory 57 as a third determination value.

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

[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 determination value in S21 in Fig. 11 can be determined by the rotor stop position detection process in Fig. 10. That is, the current value of the coil current measured at the end timing of period B in S11 in Fig. 10 can be used as the first determination value. In this case, only the process from S23 onwards is executed for the duty coefficient update process in Fig. 11, and the value determined in the latest rotor stop position detection process is used as the first determination value.

[0044] As described above, according to this embodiment, a portion of the regenerative current is consumed by flowing it through the non-excitation coil. This configuration makes it possible to suppress an increase in the power supply voltage even when the inverter 60 is controlled to speed up the decay time of the coil current. Therefore, by controlling the coil current to speed up the decay time, the time required for the measurement process of each excitation phase is shortened, thereby shortening the time required to detect the rotor stop position.

[0045] Second Embodiment Next, the second embodiment will be described, focusing on the differences from the first embodiment. In this embodiment, the change over time in the duty of the PWM signal differs from that in the first embodiment. Figure 12 shows the change over time in the duty of the PWM signal output from PWM port 58 in the UV phase measurement process in this embodiment. Note that 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 varied in an M-shape, as shown in FIG. 12 . That is, at the start of the B period, the first set period, which is the period during which the V-phase coil 74 is switched from the first state to the second state, is set to its maximum value. Thereafter, the first set period is gradually shortened over time. Then, from a certain timing until the end of the B period, the first set period is gradually increased over time. The timing at which the first set period changes from decreasing to increasing can be, for example, the timing when half the B period has elapsed since the start of the B period. This control allows the regenerative current flowing from the second terminal of the V-phase coil 74 through the V-phase high-side switching element to increase from the start of the B period, thereby rapidly increasing the voltage of the bulk electrolytic capacitor 65. Then, as the voltage of the bulk electrolytic capacitor 65 increases, the first set period is shortened to prevent the regenerative current to the DC power supply from increasing. Furthermore, the duty is increased as the coil current decreases. This configuration can reduce the change over time in the regenerative current flowing into the DC power supply during period B, thereby suppressing the voltage rise of the DC power supply.

[0047] 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 a 0.1 ms period that starts simultaneously with period B, and the duty of the PWM signal output from the WH terminal is changed in a rectangular wave shape. 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 for 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, thereby suppressing the voltage rise of the DC power supply. Therefore, by controlling the coil current to accelerate its decay time, the time required for the measurement process of each excitation phase can be shortened, and as a result, the time required for detecting the rotor stop position can be shortened.

[0049] [Other embodiments] The motor control unit 14 can be implemented as a motor control device. The motor control unit 14 and the motor control-related parts of the printer control unit 11 can be implemented as a motor control device. While the above-described embodiment has been described using the control of the motor 15F that drives the fuser 24 as an example, the present invention can also be applied to a motor that drives any rotating member of an image forming apparatus. Examples of rotating members of an image forming apparatus include rollers involved in sheet transport, photosensitive elements in the image forming unit 1, and developing rollers. Furthermore, the above-described embodiments can also be applied to a motor in which the first terminals of three or more coils are interconnected. Furthermore, the number of magnetic poles of the roller is not limited to two, and the above-described embodiments can be applied to the control of a motor with any number of poles.

[0050] The present invention can also be realized by supplying a program that realizes one or more functions of the above-described embodiments to a system or device via a network or a storage medium, and having one or more processors in the computer of the system or device read and execute the program. It can also be realized by a circuit (e.g., ASIC) that realizes one or more functions.

[0051] The disclosure of this embodiment includes the following configuration. (Configuration 1) An image forming apparatus that forms an image on a sheet conveyed through a conveyance 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 connected to each other; a motor control means for controlling the motor by controlling the potential of a second terminal different from the first terminal of the at least three coils, the motor control means controlling the motor so that a coil current flows from a first coil to a second coil among the at least three coils, and measuring the current value of the coil current, the motor control means performing a measurement process for each of a plurality of excitation phases specified by the permutation of two coils among the at least three coils, thereby detecting a stop position of the 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 to attenuate the coil current that flowed from the first coil to the second coil during the first period during a second period following the first period, and controls the coil current to flow from the second terminal of the second coil to a third coil, which is different from the first coil and the second coil, among the at least three coils, during a third period within the second period. (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 both the third terminal and 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 increases over time, and thereafter, the first setting period decreases 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 increases over time, and thereafter, the second setting period decreases 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 then 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 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 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 is a positive value at the end timing of the second period, and updates the coefficient to be smaller if the current value of the coil current flowing from the first coil to the second coil is a negative value at the end timing of the second period. (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 increases over time, and thereafter, the third setting period decreases over time. (Configuration 11) 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 plurality of excitation phases. (Configuration 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.

[0052] The invention is not limited to the above-described embodiments, and various changes and modifications can be made without departing from the spirit and scope of the invention. Accordingly, the following claims are appended to apprise the public of the scope of the invention. [Explanation of symbols]

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

Claims

1. An image forming apparatus that forms an image on a sheet conveyed through a conveyance path, A rotating member; a motor for driving the rotating member, the motor having at least three coils, each of the at least three coils having a first terminal and a second terminal, the first terminals of the at least three coils being connected to each other; a motor control means for controlling the motor by controlling the potentials of the second terminals 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 among the at least three coils and measuring a current value of the coil current for each of a plurality of excitation phases specified by the permutation of two coils among the at least three coils, thereby detecting a stop position of a rotor of the motor; Equipped with 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 to attenuate the coil current that flowed from the first coil to the second coil during the first period during a second period following the first period, and controls the coil current to flow from the second terminal of the second coil to a third coil, the third coil being different from the first coil and the second coil, during a third period within the second period, 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 both the third terminal and 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 third coil is alternately set to the first state and the third state during the third period.

2. 2. The image forming apparatus according to claim 1, 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 increases over time, and thereafter, the first set period decreases over time.

3. 2. The image forming apparatus according to claim 1, wherein the motor control means controls the third coil so that, during the third period, a second set period from when the third coil is set to the first state to when the third coil is set to the third state increases over time, and thereafter, the second set period decreases over time.

4. 2. The image forming apparatus according to claim 1, 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 then the first set period becomes longer over time.

5. 2. The image forming apparatus according to claim 1, 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 to when the third coil is set to the third state is constant during the third period.

6. 5. The image forming apparatus of claim 2, 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.

7. 7. The image forming apparatus according to claim 6, 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 is a positive value at the end timing of the second period, and updates the coefficient to be smaller if the current value of the coil current flowing from the first coil to the second coil is a negative value at the end timing of the second period.

8. The motor control means 2. The image forming apparatus according to claim 1, 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.

9. 9. The image forming apparatus according to claim 8, wherein the motor control means controls the first coil 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 increases over time, and thereafter, the third set period decreases over time.

10. 2. 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 plurality of excitation phases.

11. 11. The image forming apparatus according to claim 10, wherein the motor control unit 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