JP7577519B2 - Motor driving device and motor driving method - Google Patents

Description

The present invention relates to a motor drive device and a motor drive method.

For example, motors used in color copiers and the like are strictly required to reduce rotational irregularities (Wow flutter). For example, in a color copier, motor rotation irregularities can cause color unevenness during printing.

To address the above-mentioned issues, for example, Patent Document 1 below discloses a drive control device for a brushless motor that includes a storage means for storing advance angle information determined based on the variation in the characteristics of the Hall elements, and in which a control means controls the brushless motor based on the information stored in the storage means.

JP 2012-85370 A

In general, motor rotation irregularities include a one-revolution component (first-order rotation component) and multiple harmonic components. For example, in the case of a color copier, the first-order rotation component and the nth-order rotation component (n is a natural number determined by dividing the number of poles of the motor by 2) have a large effect on color irregularities.

The one-revolution component, i.e., the first-order rotation component (W1), is a periodic unevenness that occurs every time the motor rotates once, and is caused by factors such as the assembly accuracy of the motor. The nth-order rotation component (including harmonic components) is a component caused by the number of magnetic poles in the motor, and is caused by the installation accuracy of position detection elements such as Hall elements, and the magnetization of the magnet.

In recent years, the single rotation component and harmonic components of rotational irregularities are thought to be one of the factors that reduce the stability of the motor's rotational speed relative to the target rotational speed, and reducing rotational irregularities is important in order to achieve high-precision motor operation.

The technology of Patent Document 1 mentioned above controls a brushless motor using advance angle information based on the variation in the characteristics of the Hall elements. Therefore, even if it is possible to reduce rotational irregularities based on the variation in the characteristics of the Hall elements, it is not possible to reduce rotational irregularities caused by other factors such as the assembly accuracy of the motor.

The present invention is intended to solve the above-mentioned problems and aims to reduce uneven rotation of the motor.

A motor drive device according to a representative embodiment of the present invention includes a drive signal generation circuit that outputs a drive signal for driving the motor based on a torque command signal indicating the torque of the motor and a signal generated according to the rotation of the motor, and a motor drive circuit that drives the motor based on the drive signal output from the drive signal generation circuit. The drive signal generation circuit includes a determination unit that determines whether the rotation of the motor is stable, a rotation speed acquisition unit that acquires the value of the rotation speed of the motor when the determination unit determines that the rotation of the motor is stable, a first base signal generation unit that generates a first base signal corresponding to the theoretical rotation position of the motor based on the value of the rotation speed acquired by the rotation speed acquisition unit, and a signal generation unit that generates the drive signal based on the first base signal and the torque command signal when the determination unit determines that the rotation of the motor is stable.

1 is a diagram showing a configuration of a motor drive device according to an embodiment of the present invention; 2 is a block diagram showing an internal configuration of a drive signal generating circuit. FIG. FIG. 4 is a diagram showing an example of a change in the rotation speed of a motor over time. 5A and 5B are diagrams illustrating an example of a signal generated in a drive signal generating circuit. 5A to 5C are diagrams for explaining a method of driving a motor when the rotation speed of the motor changes, using the motor drive device according to the present embodiment. 4 is a flowchart showing a flow of processing by the motor drive device according to the present embodiment.

1. Overview of the embodiment First, an overview of a representative embodiment of the invention disclosed in this application will be described. Note that in the following description, as an example, reference numerals in the drawings corresponding to components of the invention are given in parentheses.

[1] A motor drive device (1) according to a representative embodiment of the present invention includes a drive signal generation circuit (3) that outputs a drive signal (Sd) for driving a motor (20) based on a torque command signal (St) that indicates the torque of the motor and signals (Hu, Hv, Hw, Sr) that are generated in response to the rotation of the motor, and a motor drive circuit (2) that drives the motor based on the drive signal (Sd) output from the drive signal generation circuit, and the drive signal generation circuit (3) includes a determination unit (32) that determines whether the rotation of the motor is stable. , a rotation speed acquisition unit (33) that acquires the value of the rotation speed of the motor when the determination unit determines that the rotation of the motor is stable, a first base signal generation unit (34) that generates a first base signal (Sb1) corresponding to the theoretical rotation position of the motor based on the value of the rotation speed acquired by the rotation speed acquisition unit, and a signal generation unit (30 (31, 38, 39)) that generates the drive signal based on the first base signal and the torque command signal when the determination unit determines that the rotation of the motor is stable.

[2] In the motor drive device described in [1] above, the rotation speed acquisition unit (33) may acquire the value of the rotation speed of the motor when the determination unit (32) detects that the rotation of the motor has become stable from an unstable state.

[3] In the motor drive device described in [1] or [2] above, the determination unit (32) may determine that the rotation of the motor (20) is stable when the fluctuation in the rotation speed of the motor (20) during a predetermined period of time is within a predetermined range (R).

[4] In the motor drive device described in any one of [1] to [3] above, the drive signal generation circuit (3) further includes a second base signal generation unit (37) that generates a second base signal (Sb2) corresponding to the rotational position of the motor based on a rotational position detection signal (Hu, Hv, Hw) generated in response to the rotation of the motor, and the signal generation unit (30 (31, 38, 39)) may generate the drive signal (Sd) based on the second base signal and the torque command signal (St) when the determination unit determines that the rotation of the motor is unstable.

[5] In the motor drive device described in [4] above, the signal generation unit (30 (31, 38, 39)) may include a selector (38) that selects and outputs the first base signal (Sb1) when the determination unit determines that the rotation of the motor is stable, and selects and outputs the second base signal (Sb2) when the determination unit determines that the rotation of the motor is unstable, and a sine wave drive unit (39) that generates a signal for sine wave driving the motor based on the first base signal or the second base signal output from the selector and the torque command signal (St), and outputs the signal as the drive signal (Sd).

[6] A motor driving method according to a representative embodiment of the present invention may include a first step (S13) of determining whether the rotation of the motor (20) is stable, a second step (S14) of acquiring a value of the rotation speed of the motor when it is determined in the first step that the rotation of the motor is stable, a third step (S15) of generating a first base signal (Sb1) corresponding to a theoretical rotation position of the motor based on the value of the rotation speed acquired in the second step, and a fourth step (S15) of generating a drive signal for driving the motor based on the first base signal generated in the third step and a torque command signal (St) indicating the torque of the motor when it is determined in the second step that the rotation of the motor is stable.

2. Specific Examples of the Embodiments Specific examples of the embodiments of the present invention will be described below with reference to the drawings. In the following description, components common to the respective embodiments are designated by the same reference numerals, and repeated description will be omitted.

<<Embodiment>>

Figure 1 shows the configuration of a motor drive device 1 according to an embodiment of the present invention.

The motor unit 100 shown in FIG. 1 includes a motor 20 and a motor drive device 1 that drives the motor 20. The motor unit 100 is mounted, for example, in a copier (e.g., a color copier).

The motor 20 is, for example, a brushless motor. In this embodiment, the motor 20 is a three-phase brushless motor.

The motor drive device 1 is configured to drive the motor 20, for example, by sinusoidal drive. The motor drive device 1 rotates the motor 20 by periodically passing a sinusoidal drive current through the armature coils Lu, Lv, and Lw of the motor 20.

The motor drive device 1 has a motor drive circuit 2 and a drive signal generation circuit 3. Note that the components of the motor drive device 1 shown in FIG. 1 are only a part of the whole, and the motor drive device 1 may have other components in addition to those shown in FIG. 1.

The motor drive circuit 2 outputs a drive signal to the motor 20 based on a drive signal Sd output from the drive signal generation circuit 3, which will be described later, to drive the motor 20. The motor drive circuit 2 has an inverter circuit 2a and a pre-drive circuit 2b.

The inverter circuit 2a outputs a drive signal to the motor 20 based on the output signal output from the pre-drive circuit 2b, and energizes the armature coils Lu, Lv, and Lw of the motor 20. The inverter circuit 2a is configured, for example, by arranging a pair of series circuits of two switch elements provided at both ends of a DC power supply Vcc for each phase (U phase, V phase, and W phase) of the armature coils Lu, Lv, and Lw. In each pair of two switch elements, the terminals of each phase of the motor 20 are connected to the connection point between the switch elements.

The pre-drive circuit 2b generates an output signal for driving the inverter circuit 2a based on the drive signal Sd from the drive signal generation circuit 3, and outputs it to the inverter circuit 2a.

The drive signal Sd is, for example, a PWM (Pulse Width Modulation) signal. Specifically, the drive signal Sd includes six types of PWM signals corresponding to each switch element of the inverter circuit 2a.

The pre-drive circuit 2b generates and outputs six types of drive signals Vuu, Vul, Vvu, Vvl, Vwu, and Vwl that drive each switch element of the inverter circuit 2a, for example, based on the drive signal Sd. When these drive signals are input to the inverter circuit 2a, the switch elements that make up the inverter circuit 2a perform on and off operations. This supplies power to each phase of the motor 20.

The drive signal generating circuit 3 drives the motor 20, for example, using an open-loop motor drive method.

The open loop method does not perform control to reduce the error between the actual rotation speed and the target rotation speed, but generates a drive signal based on the input torque command signal and rotation position detection signal, and drives the motor based on the generated drive signal.

The drive signal generating circuit 3, for example, receives a torque command signal St that specifies the torque of the motor 20 instead of a target rotation speed signal that indicates a target rotation speed, which is a target value for the rotation speed of the motor 20, and drives the motor 20 based on the input torque command signal St.

The torque command signal St is, for example, a signal that indicates a duty ratio corresponding to a target torque value, such as a PWM signal.

In this embodiment, the drive signal generating circuit 3 is a program processing device (e.g., a microcontroller) having a configuration in which a processor such as a CPU, various storage devices such as RAM and ROM, and peripheral circuits such as a counter (timer), an A/D conversion circuit, a D/A conversion circuit, a clock generation circuit, and an input/output I/F circuit are connected to each other via a bus or the like.

The motor drive device 1 may be configured such that the drive signal generation circuit 3 and the motor drive circuit 2 are packaged as a single integrated circuit device (IC), or the drive signal generation circuit 3 and the motor drive circuit 2 are each packaged as separate integrated circuit devices.

The drive signal generating circuit 3 receives a rotational position detection signal corresponding to the rotation of the motor 20, which is output from a position detection device attached to the motor 20. The rotational position detection device is, for example, a Hall element. For example, the motor 20 is provided with three Hall elements 25u, 25v, and 25w, each corresponding to one of the phases (U-phase, V-phase, and W-phase) of the motor 20, as the rotational position detection device.

The three Hall elements 25u, 25v, and 25w are arranged around the rotor of the motor 20 at approximately equal intervals (e.g., 120 degrees from adjacent elements). In the following description, the Hall elements 25u, 25v, and 25w may be collectively referred to as "Hall elements 25."

Hall elements 25u, 25v, and 25w each detect the magnetic poles of the rotor and output Hall signals Hu, Hv, and Hw whose voltages change according to the rotation of the rotor. The Hall signals Hu, Hv, and Hw are each input to the drive signal generation circuit 3 as rotational position detection signals.

In addition, the drive signal generating circuit 3 may be configured to input other signals corresponding to the rotational position of the rotor of the motor 20 as the rotational position detection signal instead of the Hall signals Hu, Hv, and Hw. For example, an encoder, resolver, motor current detection circuit, etc. may be provided and the detection signal may be input.

In this embodiment, as an example, the Hall signals Hu, Hv, and Hw are input to the drive signal generation circuit 3 as rotational position detection signals, and in the following description, the "Hall signals Hu, Hv, and Hw" are also referred to as the "rotational position detection signals Hu, Hv, and Hw."

The drive signal generating circuit 3 also receives a rotation speed detection signal Sr that includes information on the rotation speed of the motor 20 (rotor). The rotation speed detection signal Sr is, for example, a periodic signal (FG (Frequency Generator) signal) that has a period (frequency) that corresponds to the rotation speed (number of rotations) of the rotor.

In this embodiment, the FG signal serving as the rotation speed detection signal Sr is generated by the rotation speed detection device 26. The rotation speed detection device 26 is, for example, an FG pattern disposed on a motor board. The FG pattern serving as the rotation speed detection device 26 generates a periodic signal (FG signal) corresponding to the rotation speed of the motor 20. This FG signal is input to the drive signal generation circuit 3 as the rotation speed detection signal Sr.

The rotation speed detection signal Sr is not limited to the FG signal, and may be any signal that includes information indicating the rotation speed of the motor 20. For example, in this embodiment, a case is described in which the rotation speed detection signal Sr is generated using an FG pattern as the rotation speed detection device 26, but the present invention is not limited to this. The rotation speed detection signal Sr may be generated using other rotation speed detection devices such as an encoder or resolver, or the drive signal generation circuit 3 itself may generate the rotation speed detection signal Sr based on the Hall signals Hu, Hv, and Hw.

In addition, when the drive signal generating circuit 3 performs sensorless drive control without using the Hall elements 25u, 25v, and 25w, the drive signal generating circuit 3 may perform calculations related to known sensorless drive control to calculate the rotation speed of the motor 20 and generate the rotation speed detection signal Sr (rotation speed information).

As described above, instead of a target rotation speed signal, a torque command signal St is input to the drive signal generating circuit 3. For example, a torque command signal St output from a higher-level device (such as a control unit of a copier) provided outside the motor drive device 1 is input to the drive signal generating circuit 3.

The drive signal generation circuit 3 generates and outputs a drive signal Sd for driving the motor 20 based on the torque command signal St and signals (Hu, Hv, Hw, Sr) generated in response to the rotation of the motor 20. Although details will be described later, when the rotation of the motor 20 is stable, the drive signal generation circuit 3 acquires (measures) the rotation speed of the motor 20, generates a base signal corresponding to the theoretical rotation position of the motor 20 (rotor) based on the acquired value of the rotation speed during stable rotation, and generates the drive signal Sd based on the generated base signal and the torque command signal St.
The internal configuration of the drive signal generating circuit 3 will now be described.

Figure 2 is a block diagram showing the internal configuration of the drive signal generation circuit 3.

As shown in FIG. 2, the drive signal generation circuit 3 includes a judgment unit 32, a rotation speed acquisition unit 33, a first base signal generation unit 34, a rotation position detection unit 36, and a second base signal generation unit 37 as functional blocks for realizing sine wave drive of the motor, as well as a torque command value acquisition unit 31, a selector 38, and a sine wave drive unit 39 as the signal generation unit 30. These functional blocks are realized by the CPU in the above-mentioned MCU executing various calculations and controlling peripheral circuits such as input/output I/F circuits.

Note that in FIG. 2, the transmission and reception of signals, information, etc. between each circuit is shown as an example only for explaining the generation of the drive signal Sd.

The torque command value acquisition unit 31 is a functional unit that acquires a torque command value (target value) from the torque command signal St input to the drive signal generation circuit 3 from, for example, a higher-level device. For example, if the torque command signal St is a PWM signal that indicates the torque command value by a duty ratio, the torque command value acquisition unit 31 analyzes the duty ratio of the PWM signal as the torque command signal St and provides the analyzed value to the sine wave drive unit 39 as a torque command value.

The determination unit 32 is a functional unit that determines whether the rotation of the motor 20 is stable. The determination unit 32 monitors the rotation speed of the motor 20 based on the rotation speed detection signal Sr, and outputs a determination result signal Se that indicates whether the rotation of the motor 20 is stable by determining whether the rotation speed satisfies the stable rotation determination condition.

FIG. 3 is a diagram showing an example of a change in the rotation speed of the motor 20 over time.
In Fig. 3, the horizontal axis represents time, and the vertical axis represents the rotation speed of the motor 20. Reference numeral 300 in Fig. 3 is a graph showing the change over time in the rotation speed of the motor 20 when a torque command signal St is input from a higher-level device at time t0 and the motor drive device 1 starts driving the motor 20.

The determination unit 32 performs a determination process to determine whether the rotation of the motor 20 is stable. For example, the determination unit 32 periodically (at a predetermined period T1) sequentially performs the determination process. The predetermined period T1 is, for example, one period of the FG pattern (one period of the rotation speed detection signal Sr). For example, the determination unit 32 performs the determination process every time one period of the FG pattern is output (every period of the rotation speed detection signal Sr).

In the determination process, the determination unit 32 sequentially measures the rotation speed of the motor 20 based on the rotation speed detection signal Sr. For example, the determination unit 32 measures the rotation speed of the motor 20 by measuring the period (frequency) of the rotation speed detection signal Sr.

Next, the determination unit 32 determines whether the fluctuation in the rotation speed is within a predetermined range R (hereinafter also referred to as the "allowable fluctuation range R"). Specifically, the determination unit 32 determines whether the fluctuation in the rotation speed (e.g., the rate of fluctuation or the amount of fluctuation) when comparing the measured value of the rotation speed of the motor 20 with the rotation speed of the motor 20 at the time of the previous measurement is within the allowable fluctuation range R. For example, the determination unit 32 determines whether the rate of fluctuation of the measured value of the rotation speed is within the allowable fluctuation range R (e.g., within ±3%).

Then, if the rate of fluctuation of the measured values of the multiple rotation speeds determined in a predetermined period T1 is within the allowable fluctuation range R for a predetermined number of times or more, the determination unit 32 outputs a determination result signal Se indicating that the rotation of the motor 20 is in a stable state (hereinafter also referred to as a "stable rotation state"). If the rate of fluctuation of the measured values of the multiple rotation speeds does not continue within the allowable fluctuation range R for a predetermined number of times or more, the determination unit 32 outputs a determination result signal Se indicating that the rotation of the motor 20 is in an unstable state (hereinafter also referred to as an "unstable rotation state").

The determination by the determination unit 32 is sufficient as long as it can detect that the rate of fluctuation of the measured value of the rotation speed is continuously fluctuating within the allowable fluctuation range R, and the specific determination method is not limited to the above. For example, the predetermined period T1 may be multiple periods or a fixed period of the rotation speed detection signal Sr, and the determination unit 32 may calculate the average value of the rotation speed in the predetermined period T1, and determine that the rotation state is stable if the average value is within the allowable fluctuation range R in a second predetermined period T2 that is longer than the predetermined period T1.

In the example shown in FIG. 3, the rotation speed of the motor 20 continues to increase from time t0 to time t1, and the fluctuation rate of the rotation speed exceeds the allowable fluctuation range R (e.g., ±3%). At this time, the determination unit 32 outputs a determination result signal Se indicating that the rotation speed of the motor 20 is in an unstable state (unstable rotation state).

Thereafter, the rotation speed of the motor 20 stops increasing and approaches a constant value, causing the fluctuation rate of the rotation speed to converge within the allowable fluctuation range R. For example, if at time t2 the state in which the fluctuation rate of the rotation speed is within the allowable fluctuation range R continues for a predetermined period T2, the determination unit 32 outputs a determination result signal Se indicating that the motor 20 is in a stable rotation state.

The rotation speed acquisition unit 33 is a functional unit that acquires the value of the rotation speed of the motor 20 when the judgment unit 32 judges that the motor 20 is in a stable rotation state. Specifically, the rotation speed acquisition unit 33 measures the rotation speed of the motor 20 based on the rotation speed detection signal Sr in response to the judgment unit 32 outputting a judgment result signal Se indicating that the motor 20 is in a stable rotation state, and acquires the measured value. For example, in the example shown in FIG. 3, when the judgment unit 32 outputs a judgment result signal Se indicating that the motor 20 is in a stable rotation state at time t2, the rotation speed acquisition unit 33 measures the rotation speed of the motor 20 based on the rotation speed detection signal Sr, and acquires the measured value, for example, as a constant value.

Here, when the motor 20 is in a stable rotation state, it is preferable that the rotation speed acquisition unit 33 does not periodically acquire the value of the rotation speed, but rather acquires the value of the rotation speed when the determination unit 32 detects that the rotation of the motor 20 has changed from an unstable rotation state (unstable rotation state) to a stable rotation state (stable rotation state). For example, in each determination process by the determination unit 32, it is preferable to acquire the value of the rotation speed of the motor 20 as a constant value only when the motor 20 transitions from an unstable rotation state to a stable rotation state, rather than acquiring the value of the rotation speed of the motor 20 every time it is determined that the motor 20 is in a stable rotation state.

The value of the rotation speed acquired by the rotation speed acquisition unit 33 may be, for example, one of the measured values of the rotation speed acquired within a predetermined period T2, or may be the average value of a plurality of measured values of the rotation speed acquired within a predetermined period T2. In other words, the value of the rotation speed acquired by the rotation speed acquisition unit 33 may be a value based on the measured value of the rotation speed of the motor 20 in a stable rotation state.

The rotational position detection unit 36 is a functional unit that generates a signal indicating the rotational position of the motor 20 based on the rotational position detection signals Hu, Hv, and Hw. For example, the rotational position detection unit 36 generates a three-phase composite signal Sf that combines the three-phase hall signals Hu, Hv, and Hw. For example, the three-phase composite signal is a signal whose signal level changes every 60° electrical angle.

The first base signal generating unit 34 and the second base signal generating unit 37 are functional units that generate a base signal that serves as a reference (for example, for a 144-step sine wave, one step width = 2.5°) for generating a sine wave drive signal as the drive signal Sd described below. Here, the base signal is a signal (pulse signal) that corresponds to the rotational position of the motor 20 (rotor), and the period of the base signal corresponds to the rotational speed of the motor 20.

In this embodiment, the base signal generated by the first base signal generating unit 34 is referred to as the "first base signal Sb1," and the base signal generated by the second base signal generating unit 37 is referred to as the "second base signal Sb2."

Figure 4 shows an example of a signal generated by the drive signal generation circuit 3.

4, the second base signal generating unit 37 generates the second base signal Sb2 using the rotational position detection signals (Hall signals) Hu, Hv, and Hw generated in response to the rotation of the motor 20. Specifically, the second base signal generating unit 37 generates the second base signal Sb2 by, for example, dividing the three-phase composite signal Sf generated by the rotational position detecting unit 36 based on the three-phase Hall signals Hu, Hv, and Hw by a predetermined number.

For example, the second base signal generating unit 37 divides the three-phase composite signal Sf, which has an electrical angle of 360°, into 144 steps to generate the second base signal Sb2, which has one step of 2.5°. In this case, one period of the second base signal Sb2 corresponds to the electrical angle of the motor 20 of 2.5°.

As described above, the second base signal Sb2 is generated using the rotational position detection signals Hu, Hv, and Hw that are generated in response to the actual rotation of the motor 20, and is therefore affected by the variation in the characteristics of the Hall elements 25u, 25v, and 25w, the assembly accuracy of the motor 20, etc.

The first base signal generating unit 34 generates the first base signal Sb1 based on the rotation speed of the motor 20 when the rotation of the motor 20 is stable. Specifically, the first base signal generating unit 34 calculates the period Tb1 of the first base signal Sb1 to be generated based on the value of the rotation speed acquired by the rotation speed acquiring unit 33 as, for example, a constant value, generates a periodic signal having the calculated period Tb1, and outputs it as the first base signal Sb1.

Here, the period Tb1 of the first base signal Sb1 can be calculated based on the rotation speed (frequency) of the motor 20 in a stable rotation state and the number of pulses of the rotation speed detection signal Sr (FG signal) corresponding to the period in which the motor 20 rotates by a predetermined angle, for example, as shown below. An example of a method for calculating the period of the first base signal Sb1 is shown below.

For example, consider the case where the rotation speed of motor 20 acquired when motor 20 is in a stable rotation state is 500 [Hz], the number of pulses of the rotation speed detection signal Sr (FG signal) per rotor rotation is 45 [pulse/rev], and motor 20 is a 10-pole motor (having five pairs of north and south poles).

At this time, the period corresponding to the rotation speed of the motor 20 is given by the following formula:

1/500 (Hz) = 2 (ms)

The period of 360 electrical degrees, i.e., the period of each of the Hall signals Hu, Hv, and Hw, is calculated based on the period of the clock signal, the number of pulses of the FG signal per rotation of the rotor, and the number of magnetic poles of the motor 20. Specifically, it is expressed by the following formula.

2 (ms) * 45 (pulse/rev) / 5 (pairs) = 18 (ms)

Here, if the number of steps that determines the smoothness of the sinusoidal current flowing through the motor 20 is, for example, 144 steps, the period Tb1 of the first base signal Sb1 can be calculated from the following formula.

Tb1 = 18 (ms) / 144 (steps) = 125 (μs)

In this case, one period (Tb1) of the first base signal Sb1 corresponds to an electrical angle of 2.5° of the motor 20.

The first base signal generating unit 34 generates the first base signal Sb1 from the reference clock signal in the drive signal generating circuit 3, for example, using a counter (not shown) provided in the program processing device as the drive signal generating circuit 3. Specifically, the first base signal generating unit 34 calculates the period Tb1 by the above-mentioned method using the value of the rotation speed during stable rotation of the motor 20 acquired as a constant value by the rotation speed acquisition unit 33, for example. The first base signal generating unit 34 then sets a designated count value corresponding to the calculated period Tb1, and generates a pulse signal as the first base signal Sb1 by counting the reference clock signal up to the designated count value using the counter.

For example, if the frequency of the reference clock signal generated inside the drive signal generation circuit 3 is 10 MHz (with a period of 100 ns) and the specified count value is "1250", the first base signal generation unit 34 counts the clock signal "1250 times" to generate a periodic signal (pulse signal) with a period Tb1 of 125 μs (= 100 ns x 1250) and outputs it as the first base signal Sb1 (see Figure 4).

In this way, the first base signal Sb1 is a signal corresponding to the theoretical rotational position of the motor 20 (rotor) when it is assumed that the motor 20 is rotating at the rotational speed acquired by the rotational speed acquisition unit 33, and unlike the second base signal Sb2, it is not generated using the rotational position detection signals Hu, Hv, Hw which are generated according to the actual rotation of the motor 20, and is therefore not affected by the variation in the characteristics of the Hall elements 25u, 25v, 25w or the assembly accuracy of the motor 20.

The selector 38 is a functional unit that selects and outputs either the first base signal Sb1 output from the first base signal generating unit 34 or the second base signal Sb2 output from the second base signal generating unit 37 based on the judgment result signal Se from the judgment unit 32.

Specifically, the selector 38 selects and outputs the second base signal Sb2 when the judgment result signal Se by the judgment unit 32 is a value indicating that the motor 20 is in an unstable rotation state, and selects and outputs the first base signal Sb1 when the judgment result signal Se by the judgment unit 32 is a value indicating that the motor 20 is in a stable rotation state.

The sine wave drive unit 39 is a functional unit that generates a drive signal Sd for driving the motor drive circuit 2 based on the torque command signal St and the first base signal Sb1 or the second base signal Sb2 output from the selector 38 as a base signal.

Specifically, the sine wave drive unit 39 generates six types of PWM signals with adjusted pulse widths using the first base signal Sb1 or the second base signal Sb2 output from the selector 38 so that the motor 20 operates at the torque specified by the torque command value (torque command signal St) output from the torque command value acquisition unit 31, and outputs the PWM signals as drive signals Sd. When the drive signal Sd is input to the motor drive circuit 2, the motor drive circuit 2 drives the motor 20 in a sine wave manner.

Figure 5 is a diagram for explaining the method of driving a motor when the rotation speed of the motor changes, using the motor drive device 1 according to this embodiment.

In FIG. 5, the change over time in the rotation speed of the motor 20 from time t2 onward in FIG. 3 described above is indicated by reference numeral 301.

As shown in FIG. 5, assume that the rotation speed of the motor 20 stabilizes after time t2, and the motor 20 is in a stable rotation state. At this time, the judgment unit 32 outputs a judgment result signal Se indicating that the motor 20 is in a stable rotation state, so the selector 38 selects and outputs the first base signal Sb1 generated based on the measured value of the rotation speed of the motor 20 acquired at time t2. The sine wave driver 39 generates a drive signal Sd using the first base signal Sb1 output from the selector 38, and drives the motor 20.

After that, for example, an event occurs in a copier equipped with the motor unit 100, such as a paper jam, that causes a change in the load on the motor 20, and the rotation speed of the motor 20 changes significantly during the period from time t3 to time t4 in FIG. 5.

During the period from time t3 to time t4, the fluctuation rate of the rotation speed exceeds a predetermined range R (e.g., ±3%), so the judgment unit 32 judges that the motor 20 is in an unstable rotation state and outputs a judgment result signal Se indicating this. In response to the judgment result signal Se indicating that the motor 20 is in an unstable rotation state being output from the judgment unit 32, the selector 38 switches the base signal to be output from the first base signal Sb1 to a second base signal Sb2 based on the rotation position detection signals Hu, Hv, and Hw corresponding to the actual rotation of the motor 20. The sine wave drive unit 39 generates a drive signal Sd using the second base signal Sb2 output from the selector 38, and drives the motor 20.

Then, the paper jam or the like is cleared, the rotation speed of the motor 20 stabilizes, and at time t5, the state in which the fluctuation rate of the rotation speed is within a predetermined range R has elapsed for a predetermined period T2. At this time, the determination unit 32 switches the determination result signal Se from a value indicating that the motor 20 is in an unstable rotation state to a value indicating that the motor 20 is in a stable rotation state.

The rotation speed acquisition unit 33 acquires the value of the rotation speed of the motor 20 as a new constant value in response to the determination result signal Se switching from a value indicating that the motor 20 is in an unstable rotation state to a value indicating that the motor 20 is in a stable rotation state. As a result, the first base signal generation unit 34 generates the first base signal Sb1 using the newly acquired rotation speed value.

In response to the output of the determination result signal Se indicating that the motor 20 is in a stable rotation state, the selector 38 switches the selected base signal from the second base signal Sb2 to the first base signal Sb1 and outputs it. As a result, from time t5 onwards, the sine wave drive unit 39 again generates the drive signal Sd using the first base signal Sb1 and drives the motor 20.

Next, the flow of processing in the motor drive device 1 will be described.
FIG. 6 is a flowchart showing the flow of processing by the motor drive device 1 according to the present embodiment.

As shown in FIG. 6, first, when the torque command signal St is input to the motor drive device 1 while the motor 20 is not being driven, the drive signal generation circuit 3 detects the torque command signal St (step S11). The drive signal generation circuit 3 starts motor drive in response to the detection of the torque command signal St.

First, the drive signal generating circuit 3 generates a second base signal Sb2 based on the rotational position detection signals (Hall signals) Hu, Hv, and Hw corresponding to the actual rotation of the motor 20, and starts driving the motor 20 using the second base signal Sb2 (step S12).
Specifically, for example, when the motor 20 is started, the motor 20 starts rotating from a stopped state, and therefore the motor 20 is not in a stable rotation state. Therefore, the determination unit 32 outputs a determination result signal Se indicating that the motor 20 is in an unstable rotation state. In response to the determination result signal Se, the selector 38 selects and outputs the second base signal Sb2 generated by the second base signal generation unit 37 based on the rotation position detection signals Hu, Hv, and Hw. Then, the sine wave drive unit 39 generates and outputs the drive signal Sd based on the second base signal Sb2 and the torque command signal St, and the motor 20 starts rotating.

Next, the drive signal generating circuit 3 determines whether the rotation of the motor 20 is stable (step S13). Specifically, the determination unit 32 measures the rotation speed of the motor based on the rotation speed detection signal Sr, and periodically determines whether the motor 20 is in a stable rotation state using the method described above.

If the motor 20 is in an unstable rotation state (step S13: NO), the drive signal generation circuit 3 continues to drive the motor using the second base signal Sb2 based on the rotation position detection signals Hu, Hv, and Hw corresponding to the actual rotation of the motor 20 (step S12).

On the other hand, if the motor 20 is in a stable rotation state (step S13: YES), the drive signal generation circuit 3 acquires the value of the rotation speed of the motor 20 in the stable rotation state (step S14). For example, when the judgment result signal Se output from the judgment unit 32 switches from a value indicating that the motor 20 is in an unstable rotation state to a value indicating that the motor 20 is in a stable rotation state, the rotation speed acquisition unit 33 acquires the value of the rotation speed of the motor 20 as a constant value using the above-mentioned method.

Next, the drive signal generating circuit 3 drives the motor 20 using the first base signal Sb1 based on the rotation speed value acquired in step S14 (step S15). Specifically, in response to the output of the judgment result signal Se from the judgment unit 32 in step S13 indicating that the motor 20 is in a stable rotation state, the selector 38 selects and outputs the first base signal Sb1 based on the rotation speed value acquired by the rotation speed acquisition unit 33 in step S14. Then, the sine wave drive unit 39 generates and outputs the drive signal Sd based on the first base signal Sb1 and the torque command signal St, causing the motor 20 to rotate.

Then, the drive signal generating circuit 3 determines whether the motor 20 continues to rotate stably (step S16). If the motor 20 is not in a stable rotation state but in an unstable state (step S16: NO), the drive signal generating circuit 3 switches the motor drive from using the first base signal Sb1 to using the second base signal Sb2 (Hall signal) (step S12). After that, the drive signal generating circuit 3 executes the above-mentioned steps S13 to S16 again.

If the motor 20 continues to rotate stably (step S16: YES), the drive signal generating circuit 3 detects whether the input of the torque command signal St has stopped (step S17).

If the input of the torque command signal St has not stopped (step S17: NO), the drive signal generating circuit 3 continues to drive the motor using the first base signal Sb1 based on the rotation speed obtained in step S14 (step S15).

On the other hand, if the input of the torque command signal St is stopped (step S17: YES), the drive signal generating circuit 3 starts the free-run stop process for the motor 20 (step S18). That is, the drive signal generating circuit 3 generates the drive signal Sd to turn off all phases of the motor 20. This causes the motor 20 to free-run to a stop. When stopping, a short brake or the like may be performed.

The characteristics of the rotational irregularities of the motor 20 are that the variations due to the assembly accuracy of the motor 20 and the uneven magnetization of the magnets result in rotational irregularities that occur periodically every time the motor 20 rotates once. In addition, the variations due to the installation accuracy of the Hall element 25 result in rotational irregularities of harmonic components that occur periodically during one rotation of the motor 20.

In contrast, in the motor drive device 1 according to the present embodiment, when the motor 20 is rotating stably, the base signal used by the sine wave drive unit 39 to generate the drive signal Sd (PWM signal) is the first base signal Sb1 based on the rotation speed of the motor 20 acquired when the motor 20 is in a stable rotation state. In other words, the first base signal Sb1 is not a signal generated based on the Hall signals Hu, Hv, and Hw, which vary depending on the actual rotation of the motor 20, but is a signal theoretically calculated from the value of the rotation speed, assuming that the motor 20 rotates at a constant rotation speed without fluctuation. Therefore, the first base signal Sb1 does not vary due to variations caused by uneven magnetization of the magnet of the motor 20, variations due to the installation accuracy of the Hall element 25, etc.

Therefore, when the motor 20 is rotating stably, the motor 20 is driven by the drive signal Sd generated based on the first base signal Sb1, so that the rotational irregularities caused by the above-mentioned assembly accuracy of the motor 20, uneven magnetization of the magnet, and variations due to the installation accuracy of the Hall element 25 can be suppressed.

In addition, the motor drive device 1 according to this embodiment determines whether the motor 20 is in a stable rotation state, obtains the rotation speed of the motor 20 when it is in a stable rotation state, and generates the drive signal Sd. This makes it possible to drive the motor with reduced rotational irregularities not only when the target rotation speed is not specified by a higher-level device, as in the open-loop method, but also when the target rotation speed specified by the higher-level device changes, as in the closed-loop method.

Here, the closed-loop method refers to a method in which, when a target rotation speed signal that specifies the target rotation speed of the motor is input from an external device (e.g., a higher-level device), a drive signal is generated so as to reduce the error between the measured actual rotation speed of the motor and the target rotation speed signal, and the motor is driven based on the generated drive signal.

In addition, the motor drive device 1 according to this embodiment acquires the value of the rotation speed of the motor 20 when it detects that the rotation of the motor 20 has become stable from an unstable state, thereby making it possible to effectively suppress rotation unevenness.

For example, when the rotation speed of the motor 20 fluctuates within a predetermined range R, if the rotation speed of the motor 20 is continuously acquired, the acquired rotation speed value will vary, and the first base signal Sb1 generated based on it will also vary. As a result, there is a possibility that the rotation unevenness of the motor 20 cannot be effectively suppressed.

In contrast, the motor drive device 1 according to the present embodiment acquires the value of the rotation speed of the motor 20 upon detecting that the rotation of the motor 20 has stabilized from an unstable state, and uses the acquired value as, for example, a constant value. If the stable rotation state continues, the motor drive device 1 generates the first base signal Sb1 using the acquired rotation speed value (constant value).
According to this, even if the motor 20 is in a stable rotation state but the rotation speed of the motor 20 fluctuates within a predetermined range R, a stable first base signal Sb1 can be generated without being affected by minute fluctuations in the rotation speed, making it possible to effectively suppress rotation unevenness of the motor 20.

When the rotation of the motor 20 is stable, the motor drive device 1 drives the motor 20 using a first base signal Sb1 based on the acquired rotation speed of the motor 20, and when the rotation of the motor 20 is unstable, the motor drive device 1 drives the motor 20 using a second base signal Sb2 based on the rotation position detection signals (Hall signals) Hu, Hv, and Hw corresponding to the actual rotation of the motor 20.

This allows the motor 20 to rotate with an appropriate torque according to the load of the motor 20 in situations where the rotation of the motor 20 is unstable, such as when the motor 20 is started or when the load fluctuates, and also allows the rotation unevenness of the motor 20 to be suppressed in situations where the rotation of the motor 20 is stable. In other words, it is possible to achieve both appropriate motor driving according to the load and suppression of rotation unevenness.

<<Extension of the embodiment>>
The invention made by the inventor has been specifically described above based on an embodiment, but it goes without saying that the invention is not limited thereto and can be modified in various ways without departing from the spirit of the invention.

For example, in the above embodiment, the drive signal generation circuit 3 is not limited to the circuit configuration shown above. The drive signal generation circuit 3 can be configured in a variety of circuit configurations that are suited to the purpose of the present invention.

The above-mentioned flowchart is a specific example, and the present invention is not limited to this flowchart. For example, other processes may be inserted between each step, or the processes may be parallelized.

The number of phases of the motor driven by the motor drive device of the above embodiment is not limited to three. Also, the number of Hall elements is not limited to three.

The method of detecting the rotational position and rotational speed of the motor is not particularly limited. For example, instead of using a Hall element or FG pattern, the rotational position may be detected using another rotational position detection device, and the rotational speed may be detected by another rotational speed detection device or by calculation based on the motor current, the back electromotive force of the motor, etc.

The motor drive method is not limited to the sine wave drive method. For example, it can be applied to a trapezoidal wave or a drive method that applies special modulation to a sine wave.

A part or all of the processing in the above-described embodiment may be performed by software or by using hardware circuits. In other words, each component of the motor drive device 1 may be configured so that at least a part of it is realized by software processing rather than hardware processing.

1...motor drive device, 2...motor drive circuit, 2a...inverter circuit, 2b...pre-drive circuit, 3...drive signal generation circuit, 20...motor, 25u, 25v, 25w...hall elements, 26...rotational speed detection device, 30...signal generation unit, 31...torque command value acquisition unit, 32...judgment unit, 33...rotational speed acquisition unit, 34...first base signal generation unit, 36...rotational position detection unit, 37...second base signal generation unit, 38...selector, 39...sine wave drive unit, 100...motor unit, Hu, Hv, Hw...rotational position detection signal (hall signal), Sb1...first base signal, Sb2...second base signal, Sd...drive signal, Se...judgment result signal, Sr...rotational speed detection signal, St...torque command signal.

Claims (6)

a drive signal generating circuit that outputs a drive signal for driving the motor based on a torque command signal that indicates a torque of the motor and a signal that is generated in response to the rotation of the motor;
a motor drive circuit that drives the motor based on the drive signal output from the drive signal generation circuit;
The drive signal generating circuit includes:
a determination unit that determines whether the rotation of the motor is stable;
a rotation speed acquisition unit that measures a value of a rotation speed of the motor when the determination unit determines that the rotation of the motor is stable, and acquires the measured value of the rotation speed as a constant value ;
a first base signal generating unit that generates a first base signal corresponding to a theoretical rotational position of the motor based on the constant value acquired by the rotation speed acquiring unit;
a signal generating unit configured to generate the drive signal based on the first base signal and the torque command signal when the determining unit determines that rotation of the motor is stable. 2. The motor drive device according to claim 1,
the determination unit measures the rotation speed at predetermined intervals, determines whether or not rotation of the motor is stable based on the measured value of the rotation speed, and outputs a determination result signal indicating a value indicating that rotation of the motor is stable or a value indicating that rotation of the motor is unstable;
The motor drive device, wherein the rotation speed acquisition unit measures the value of the rotation speed in response to the determination result signal switching from a value indicating that the rotation of the motor is unstable to a value indicating that the rotation of the motor is stable , and acquires the measured value of the rotation speed as the constant value . 3. The motor drive device according to claim 1,
The motor drive device, wherein the determination unit determines that rotation of the motor is stable when a fluctuation in the rotation speed over a predetermined period of time is within a predetermined range. 4. The motor drive device according to claim 1,
The drive signal generating circuit includes:
a second base signal generating unit configured to generate a second base signal corresponding to a rotational position of the motor based on a rotational position detection signal generated in response to rotation of the motor,
The signal generating unit generates the drive signal based on the second base signal and the torque command signal when the determining unit determines that rotation of the motor is not stable. 5. The motor drive device according to claim 4,
The signal generating unit
a selector that selects and outputs the first base signal when the determination unit determines that the rotation of the motor is stable, and selects and outputs the second base signal when the determination unit determines that the rotation of the motor is unstable;
a sine wave driving unit that generates a signal for sinusoidally driving the motor based on the first base signal or the second base signal output from the selector and the torque command signal, and outputs the signal as the drive signal. A first step of determining whether or not the rotation of the motor is stable;
a second step of measuring a rotation speed of the motor when it is determined in the first step that the rotation of the motor is stable, and acquiring the measured rotation speed value as a constant value ;
a third step of generating a first base signal corresponding to a theoretical rotational position of the motor based on the constant value obtained in the second step;
a fourth step of generating a drive signal for driving the motor based on the first base signal generated in the third step and a torque command signal that indicates a torque of the motor when it is determined in the second step that the rotation of the motor is stable.

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