JP2024142847A - MOTOR DRIVE CONTROL DEVICE, ACTUATOR, AND MOTOR DRIVE CONTROL METHOD - Google Patents

Abstract

To appropriately control a coil current of a motor.SOLUTION: A motor drive control device 10 compares a measurement value Si of a current of a coil 21 with a current reference value Sis on a PWM cycle basis, designates a charge mode as an excitation mode of the coil 21 in a case where the measurement value Si of the current does not reach the current reference value Sis, and designates an attenuation mode as the excitation mode of the coil 21 in a case where the measurement value Si of the current reaches the current reference value Sis. When attenuating a coil current in a mixed attenuation mode in which a coil current is regenerated by combining a low-speed attenuation mode with a high-speed attenuation mode, in a case where it is detected that the coil current reaches the current reference value, the motor drive control device 10 performs increase processing for making a ratio of a period of the high-speed attenuation mode in an attenuation period within the PWM cycle larger than a ratio of a period of the high-speed attenuation mode in an attenuation period within the preceding PWM cycle.SELECTED DRAWING: Figure 8

Description

The present invention relates to a motor drive control device, an actuator, and a motor drive control method, and more particularly to a motor drive control device for driving a stepping motor, an actuator equipped with the motor drive control device, and a motor drive control method for driving a stepping motor.

Conventionally, a method for controlling the drive of motors such as stepping motors and brushless DC motors is known in which the coil is driven so that the coil current, which is the current flowing through the coil of the motor, becomes sinusoidal.

For example, in the microstep method, which is one of the driving methods for stepping motors, the motor drive control device changes the reference current value (command value) in a stepped manner so that the coil current of each phase that makes up the stepping motor becomes sinusoidal, while also monitoring the coil current and switching the excitation state of the coil of each phase so that the detected value of the coil current does not exceed the reference value.

In general, in the microstep method, the coil current is controlled to have a sinusoidal waveform by alternating between periods in which the coil current is increased in a positive or negative direction and periods in which the coil current is changed toward zero, depending on the electrical angle θ (rotor position) of the stepping motor.

Generally, when controlling the drive of a stepping motor using the microstep method, two control methods (excitation modes) for decaying the current are known: a slow decay mode that regenerates the coil current, and a fast decay mode that regenerates the current faster than the slow decay mode (see, for example, Patent Document 1).

JP 2006-254542 A

In conventional microstep driving methods for stepping motors, the coil current is generally gradually decreased in slow decay mode during the first specified period of the decay period in which the coil current is changed toward zero, and then the coil current is rapidly decreased in fast decay mode during the subsequent period.

In the conventional driving method described above, when switching from the slow decay mode to the fast decay mode during the decay period, the amount of decay of the coil current changes significantly. This change in the amount of decay of the coil current causes a large distortion (ripple) in the coil current waveform, and this distortion can cause the stepping motor to make a loud abnormal noise.

On the other hand, if the time in the slow decay mode is made longer than that in the fast decay mode during the decay period in order to reduce the ripple in the coil current, the coil current may not be sufficiently reduced and may not be able to change into a sinusoidal wave.

The present invention was made in consideration of the above-mentioned problems, and aims to appropriately control the coil current of a motor.

A motor drive control device according to a representative embodiment of the present invention includes a control circuit that generates a drive control signal for controlling the drive of a motor, and a drive circuit that excites a coil of the motor based on the drive control signal. The control circuit includes a current value acquisition unit that acquires a measured value of a coil current that is a current flowing through the coil, a drive control signal generation unit that generates a PWM signal so that the coil is in a state corresponding to a specified excitation mode and outputs the PWM signal as the drive control signal, a current reference value setting unit that sets a current reference value that is a reference for the coil current for each PWM period of the PWM signal so that the current flowing through the coil changes in a sinusoidal shape, and an excitation control unit that designates a charge mode that increases the coil current as the excitation mode when the measured value of the coil current measured by the current value acquisition unit is lower than the current reference value for each PWM period, and designates a decay mode that decreases the coil current as the excitation mode when the measured value of the coil current is equal to or greater than the current reference value. and a magnetic mode designation unit, the decay modes including a slow decay mode in which the coil current is regenerated, a fast decay mode in which the coil current is regenerated faster than the slow decay mode, and a mixed decay mode in which the coil current is regenerated by combining the slow decay mode and the fast decay mode, and when the coil current is attenuated by the mixed decay mode, the excitation mode designation unit first designates one of the slow decay mode and the fast decay mode in a decay period in which the coil current is attenuated in one of the PWM cycles, and then designates the other of the slow decay mode and the fast decay mode, and when the excitation mode designation unit detects that the coil current has reached the current reference value in the mixed decay mode, it performs an increase process to make the proportion of the period of the fast decay mode in the decay period in the PWM cycle greater than the proportion of the period of the fast decay mode in the decay period in the previous PWM cycle.

The motor drive control device according to the present invention makes it possible to appropriately control the coil current of the motor.

1 is an exploded perspective view showing an example of the structure of an actuator equipped with a motor drive control device according to an embodiment; FIG. 2 is a diagram illustrating a schematic configuration of a motor and a motor drive control device. 1 is a block diagram showing a configuration of a motor drive control device according to an embodiment; FIG. 13 is a diagram for explaining a charge mode. FIG. 13 is a diagram for explaining a slow decay mode. FIG. 13 is a diagram for explaining a fast decay mode. 4 is a timing chart showing changes over time in a coil current and a drive control signal of a motor. FIG. 6 is an enlarged view of a portion of the current decay period TD in FIG. 5 . FIG. 11 is a diagram showing an example of a change in coil current over time in a first attenuation period Td1. FIG. 13 is a diagram showing an example of a change in coil current over time in a second attenuation period Td2. 13 is a flowchart showing an example of the flow of an increasing process for increasing the period of the fast decay mode in the mixed decay mode. FIG. 11 is a diagram showing the results of measuring coil current when a motor is driven by a motor drive control device according to a prior study example by the present inventors, as a comparative example. 7A and 7B are diagrams showing actual measurement results of coil current when a motor is driven by the motor drive control device according to the embodiment.

Specific examples of embodiments of the present invention will be described below with reference to the drawings. In the following description, components common to each embodiment will be given the same reference numerals, and repeated description will be omitted.

Figure 1 is an exploded perspective view showing an example of the structure of an actuator equipped with a motor drive control device according to an embodiment.

The actuator (motor unit) 1 is, for example, a device for driving an air conditioner in an HVAC (Heating Ventilation and Air-Conditioning) system as an air conditioning unit for vehicle use. Examples of the actuator 1 include various actuators that can be used in HVAC systems, such as a damper actuator, a valve actuator, a fan actuator, and a pump actuator.

In an HVAC system, actuator 1 is connected to, for example, other actuators via a bus to an ECU (not shown) as a higher-level device, forming a LIN (Local Interconnect Network) communication network.

As shown in FIG. 1, the actuator 1 is covered with a case 51 and a cover 52. Inside the actuator 1 are housed a motor 20, a motor drive control device 10 that controls the drive of the motor 20, and a primary gear 26, a secondary gear 31, a tertiary gear 32, and an output gear 33 that serve as a power transmission mechanism that transmits the rotational force of the motor 20 to a driven object.

The motor 20 generates the driving force for the actuator 1. The motor 20 is, for example, a stepping motor. In this embodiment, the motor 20 is described as being a two-phase stepping motor having an A-phase coil and a B-phase coil. The motor 20 operates by supplying driving power to the coils of each phase from the motor drive control device 10, as described below.

Figure 2 is a diagram showing a schematic configuration of the motor 20 and the motor drive control device 10.

As described above, the motor 20 is a two-phase stepping motor. As shown in FIG. 2, the motor 20 has an A-phase coil 21a, a B-phase coil 21b, a rotor 22, and a two-phase stator (not shown).

The coils 21a and 21b are coils that excite a stator (not shown). The coil 21a has a positive terminal AP and a negative terminal AN as the motor terminals 29. The coil 21b has a positive terminal BP and a negative terminal BN as the motor terminals 29. The positive terminal AP and the negative terminal AN of the coil 21a and the positive terminal BP and the negative terminal BN of the coil 21b are connected to the inverter circuits 143a and 143b that constitute the drive circuit 14. The inverter circuits 143a and 143b will be described in detail later.

The coils 21a and 21b are driven by inverter circuits 143a and 143b. As a result, currents Ia and Ib with different phases flow through the coils 21a and 21b. For example, currents Ia and Ib with a phase difference of 90 degrees flow through the coils 21a and 21b.

In the following description, when there is no need to distinguish between coil 21a and coil 21b, they will simply be referred to as "coil 21."

The rotor 22 is equipped with a multi-pole magnetized permanent magnet such that the south pole 22s and the north pole 22n alternate along the circumferential direction. Note that FIG. 2 shows, as an example, a case in which the rotor 22 has two poles.

The stator (not shown) is disposed around the rotor 22 and close to the outer periphery of the rotor 22. The rotor 22 rotates by periodically switching the phase of the coil current flowing through each of the coils 21a and 21b. The rotor 22 is connected to an output shaft 25, which is driven by the rotational force of the rotor 22.

As shown in FIG. 1, a primary gear 26 is attached to the output shaft 25 of the motor 20. The primary gear 26 of the motor 20 meshes with a secondary gear 31. The secondary gear 31 meshes with a tertiary gear 32. The tertiary gear 32 meshes with an output gear 33. An external output gear (not shown) provided on the output gear 33 is exposed on the bottom surface of the case 51, and this external output gear is connected to a driven object.

The motor drive control device 10 is a device for driving the motor 20. The motor drive control device 10 communicates with a higher-level device (ECU) via a bus, for example. The motor drive control device 10 controls the rotation and stop of the motor 20 by controlling the energization state of the coils 21a and 21b of each phase of the motor 20 based on a drive command Sc, which is a control frame received from the higher-level device, thereby controlling the operation of the actuator 1 as a whole. When the motor drive control device 10 drives the motor 20, the primary gear 26 connected to the output shaft 25 of the motor 20 rotates. The driving force generated by the rotation of the primary gear 26 is transmitted in order to the secondary gear 31, the tertiary gear 32, the output gear 33, and the external output gear, and the external output gear drives the moving parts of the air conditioner that is the driving target.

As shown in FIG. 1, the motor drive control device 10 has, as hardware resources, for example, a printed circuit board 42 and a flexible printed circuit board 43 that connects the printed circuit board 42 to the motor terminals 29 of the motor 20. The printed circuit board 42 is provided with a control circuit 12, a drive circuit 14, and a number of external connection terminals 41.

The circuit housed inside the case 51 and the cover 52 may be only the drive circuit 14. For example, the motor drive control device 10 may be configured with the drive circuit 14 provided inside the case 51 and the cover 52 and the control circuit 12 provided outside the case 51 and the cover 52.

As shown in FIG. 2, the motor drive control device 10 includes a control circuit 12 and a drive circuit 14.

The control circuit 12 generates a PWM signal as a drive control signal for controlling the drive of the motor 20 so that the coil current, which is the current flowing through the coil 21 of the motor 20, coincides with a current reference value, which is a target value of the coil current. Specifically, the control circuit 12 generates a drive control signal Sda for exciting the A-phase coil 21a of the motor 20 and a drive control signal Sdb for exciting the B-phase coil 21b of the motor 20 based on a drive command Sc from a higher-level device (ECU), and supplies these to the drive circuit 14 to control the rotation of the motor 20. In the following description, when the drive control signal Sda and the drive control signal Sdb are not distinguished from each other, the drive control signal Sda and the drive control signal Sdb are referred to as "drive control signal Sd."

The drive command Sc is a signal that indicates a target state of the motor 20. The drive command Sc includes, for example, information that specifies the rotation speed of the motor 20 and information that specifies a target rotation angle (target rotation position) of the motor 20.
The control circuit 12 will be described in detail later.

The drive circuit 14 controls the energization of the coil 21 of the motor 20 based on the drive control signal Sd output from the control circuit 12. The drive circuit 14 has an inverter circuit 143 for driving the coil 21 of the motor 20 and a current sensor 144 for detecting the current flowing through the coil 21 of the motor 20.

The inverter circuit 143 supplies driving power to the motor 20 based on the drive control signal Sd. As shown in FIG. 2, the inverter circuit 143 is provided, for example, for each of the coils 21a, 21b to be driven. For example, as shown in FIG. 2, an inverter circuit 143a for driving the A-phase coil 21a and an inverter circuit 143b for driving the B-phase coil 21b are provided. The inverter circuits 143a, 143b are, for example, configured with an H-bridge circuit.

In the following description, when there is no need to distinguish between inverter circuit 143a and inverter circuit 143b, inverter circuit 143a and inverter circuit 143b may be referred to as "inverter circuit 143."

As shown in FIG. 2, the inverter circuit 143a is connected to the positive terminal AP of the A-phase coil 21a and the negative terminal AN of the coil 21a. The inverter circuit 143b is connected to the positive terminal BP of the B-phase coil 21b and the negative terminal BN of the coil 21b.

The inverter circuit 143a applies a voltage Va between the positive terminal AP and the negative terminal AN based on the drive control signal Sda output from the control circuit 12, thereby causing a current Ia to flow through the coil 21a. The inverter circuit 143b applies a voltage Vb between the positive terminal BP and the negative terminal BN based on the drive control signal Sdb output from the control circuit 12, thereby causing a current Ib to flow through the coil 21b.

For example, when the A-phase coil 21a is excited to the positive side, that is, when a current Ia (+) flows from the positive terminal AP of the coil 21a to the negative terminal AN, the voltage Va of the positive terminal AP relative to the negative terminal AN is made "positive". On the other hand, when the A-phase coil 21a is excited to the negative side, that is, when a current Ia (-) flows from the negative terminal AN to the positive terminal AP of the coil 21a, the voltage Va of the positive terminal AP relative to the negative terminal AN is made "negative". The same is true when exciting the B-phase coil 21b. In the following description, the current flowing through the coil 21a may be referred to as "coil current Ia", and the current flowing through the coil 21b may be referred to as "coil current Ib".

The specific circuit configuration of the inverter circuit 143 and the specific method of exciting the coil 21 by the inverter circuit 143 will be described later.

As shown in FIG. 2, the current sensor 144 is provided, for example, for each of the coils 21a and 21b to be driven. For example, as shown in FIG. 2, a current sensor 144a is provided for detecting the coil current Ia flowing through the A-phase coil 21a, and a current sensor 144b is provided for detecting the coil current Ib flowing through the B-phase coil 21b.

Current sensors 144a, 144b each include a shunt resistor that converts the coil currents Ia, Ib of the coils 21a, 21b to be detected into a voltage. As will be described in detail later, a shunt resistor is provided for each of the coils 21a, 21b of each phase, and is connected in series with the inverter circuits 143a, 143b to the ground potential GND side or power supply voltage VDD of the inverter circuits 143a, 143b. Current sensor 144a outputs the voltage across the shunt resistor as a current detection signal Via that represents the measured value of the coil current Ia of phase A. Current sensor 144b outputs the voltage across the shunt resistor as a current detection signal Vib that represents the measured value of the coil current Ib of phase B.

The control circuit 12 is a program processing device (e.g., a microcontroller: MCU (Micro Control Unit)) that has hardware elements such as a processor such as a CPU (Central Processing Unit), various memories such as a ROM (Read Only Memory) and a RAM (Random Access Memory), a timer, a counter, an A/D conversion circuit, an input/output I/F circuit, and a clock generation circuit, and each component is connected to each other via a bus or a dedicated line. The control circuit 12 has a rewritable non-volatile storage device such as a flash memory or an EEPROM (Electrically Erasable Programmable Read-Only Memory) as a memory.

The control circuit 12 mainly has a function of controlling the energization of the motor 20 so that the motor 20 is in a state specified by the drive command Sc. Specifically, the control circuit 12 generates drive control signals Sda, Sdb to drive the inverter circuits 143a, 143b so as to excite the A-phase coil 21a and the B-phase coil 21b at a predetermined timing based on a predetermined excitation method, thereby moving (rotating) the motor 20 to the target rotation position specified by the drive command Sc.

The specified excitation method here is, for example, any of the well-known one-phase excitation method, two-phase excitation method, one-two phase excitation method, and microstep method. In this embodiment, an example will be described in which the specified excitation method is the two-phase microstep method.

The control circuit 12 generates the drive control signal Sd by a two-phase microstep method. For example, the control circuit 12 changes the current reference values (target current values) Sisa and Sisb, which are the target values of the coil currents, in a stepwise manner so that the coil currents Ia and Ib of the coils 21a and 21b of each phase constituting the motor 20 become sinusoidal, and monitors the coil currents Ia and Ib, switching the excitation state of the coils 21a and 21b of each phase so that the measured values Sia and Sib of the coil currents Ia and Ib do not exceed the current reference values Sisa and Sisb. More specifically, the control circuit 12 generates PWM signals (drive control signals Sda and Sdb) for each phase whose pulse width changes depending on the magnitude relationship between the measured values Sia and Sib of the coil currents Ia and Ib of the motor 20 and the current reference values Sisa and Sisb, and performs PWM control to control the drive of the motor 20 via the drive circuit 14.

Figure 3 is a diagram showing the functional block configuration of the control circuit 12 in the motor drive control device according to the embodiment.

As shown in FIG. 3, the control circuit 12 has, as functional blocks for realizing the above-mentioned functions, for example, a current value acquisition unit 120, a comparison unit 121, a current reference value setting unit 122, a memory unit 123, an excitation mode designation unit 124, and a drive control signal generation unit 126. These functional blocks are realized by the processor in the above-mentioned MCU executing various calculations according to programs stored in the memory and controlling peripheral circuits such as timers and counters, A/D conversion circuits, and input/output I/F circuits.

In addition to the above functions, the control circuit 12 may also have a function to determine whether or not the motor 20 has lost synchronization based on the back electromotive force of the motor 20.

The drive control signal generating unit 126 is a functional unit that generates PWM signals as the drive control signals Sda and Sdb. Hereinafter, one period of the PWM signal, i.e., the period in which one PWM signal is generated, is referred to as a "PWM period." Details of the drive control signal generating unit 126 will be described later.

The current value acquisition unit 120 is a functional unit that acquires the measured values Sia and Sib of the coil currents Ia and Ib of each phase of the motor 20. The current value acquisition unit 120 is configured to include, for example, an A/D conversion circuit.

The current value acquisition unit 120 receives current detection signals Via and Vib, which are voltages corresponding to the coil currents Ia and Ib of each phase, output from the current sensors 144a and 144b (shunt resistors). The current value acquisition unit 120 calculates the measurement values Sia and Sib of the coil currents Ia and Ib of each phase based on the magnitude (voltage) of the input current detection signals Via and Vib.

For example, the current value acquisition unit 120 converts the voltage of the current detection signal Via into a digital value and outputs it as the measurement value Sia of the A-phase coil current Ia. The current value acquisition unit 120 also converts the voltage of the current detection signal Vib into a digital value and outputs it as the measurement value Sib of the B-phase coil current Ib. The current value acquisition unit 120 outputs, for example, the measurement value Sia of the A-phase coil current Ia and the measurement value Sib of the B-phase coil current Ib for each PWM period. Hereinafter, when there is no distinction between the measurement value Sia of the coil current Ia and the measurement value Sib of the coil current Ib, the measurement value Sia of the coil current Ia and the measurement value Sib of the coil current Ib are referred to as the "measurement value Si of the coil current."

The current reference value setting unit 122 is a functional unit that sets the current reference values Sisa and Sisb that are the references for the coil currents Ia and Ib of each phase. The current reference value setting unit 122 sets the current reference values Sisa and Sisb for each PWM period so that the currents Ia and Ib flowing through the coil 21 change in a sinusoidal manner. For example, the current reference value setting unit 122 changes the current reference values Sisa and Sisb in a stepwise manner in response to an instruction from the drive command acquisition unit 131, which will be described later, so that the coil current Ia of phase A and the coil current Ib of phase B become sinusoidal and the phases of the coil current Ia and the coil current Ib differ from each other by 90 degrees. Hereinafter, when the current reference value Sisa and the current reference value Sisb are not distinguished from each other, the current reference value Sisa and the current reference value Sisb are referred to as the "current reference value Sis".

For example, the memory unit 123 stores current reference value information that indicates the correspondence between the electrical angle θ and the current reference value Sis. Here, the current reference value information is information (e.g., a function or a table) in which the current reference value Sis is associated with each electrical angle θ so that the current reference value Sis has a sinusoidal shape in the range of electrical angle θ = 0 to 360°.

The current reference value setting unit 122 reads out the current reference values Sisa and Sisb corresponding to the electrical angle θ at that time from the current reference value information stored in the memory unit 123 for each PWM period, and outputs them sequentially.

The memory unit 123 is a functional unit for storing various data necessary for driving and controlling the motor 20. At least a part of the memory unit 123 is realized, for example, by utilizing a memory area of a non-volatile storage device that retains data even when the power supply to the control circuit 12 is stopped.

In addition to the current reference value information described above, the storage unit 123 stores, for example, a minimum time Tmin, a unit increase time ΔT, specified times Tf1 and Tf2, and an upper limit time Tlmt. Details of this information will be described later.

The comparison unit (e.g., CLDAC) 121 compares the measured value Si of the coil current acquired by the current value acquisition unit 120 with the current reference value Sis for each PWM period. For example, the comparison unit 121 starts comparing the measured value Sia of the coil current Ia with the current reference value Sisa at the start of one PWM period of phase A, and outputs the comparison result Scma. Also, at the start of one PWM period of phase B, the comparison unit 121 starts comparing the measured value Sib of the coil current Ib with the current reference value Sisb, and outputs the comparison result Scmb.

When there is no need to distinguish between the comparison result ScMa and the comparison result Scmb, the comparison result ScMa and the comparison result Scmb will be referred to as the "comparison result Scm."

For example, when one PWM period starts, the comparison unit 121 starts a comparison process between the measured value Si of the coil current and the current reference value Sis. Specifically, when the measured value Si of the coil current is lower than the current reference value Sis (Si<Sis), the comparison unit 121 outputs a signal of a first logic level (e.g., high level) as the comparison result Scm. On the other hand, when the measured value Si of the coil current is equal to or greater than the current reference value Sis (Si≧Sis), the comparison unit 121 outputs a signal of a second logic level (e.g., low level) opposite to the first logic level as the comparison result Scmb, and maintains the output of the comparison result Scmb (low level) regardless of the magnitude relationship between the measured value Si of the coil current and the current reference value Sis until the end of that PWM period. Then, when one PWM period ends and the next PWM period starts, the comparison unit 121 starts a comparison process between the measured value Si of the coil current and the current reference value Sis again.

In this way, the comparison unit 121 repeatedly performs the comparison process for the coil currents Ia and Ib of each phase for each PWM period of each phase. This makes it possible to determine whether the coil current of the motor 20 has reached the current reference value by referring to the comparison result Scmb by the comparison unit 121.

The drive control signal generation unit 126 includes a drive command acquisition unit 127 and a PWM signal generation unit 128.

The drive command acquisition unit 127 acquires the drive command Sc input from, for example, a higher-level device (ECU). As described above, the drive command Sc includes, for example, information specifying the target rotational position (target rotational position) of the motor 20. The drive command acquisition unit 127 analyzes the drive command Sc to acquire and output information on the target rotational position of the motor 20, and instructs other functional units (for example, the current reference value setting unit 122, the excitation mode designation unit 124, and the PWM signal generation unit 128) to start processing for driving the motor 20.

The PWM signal generating unit 128 generates a PWM signal so that the coil 21 of the motor 20 is in an excitation state according to the specified excitation mode, and outputs the PWM signal as the drive control signals Sda and Sdb.

For example, the PWM signal generating unit 128 acquires information on the target rotation position output from the drive command acquiring unit 127. The PWM signal generating unit 128 generates a PWM signal for each phase according to the excitation mode specified by the excitation mode specifying unit 124 so that the motor 20 moves to the target rotation position, and outputs the PWM signal as the drive control signals Sda and Sdb.

The excitation mode designation unit 124 is a functional unit that designates an excitation mode and instructs the drive control signal generation unit 126 to generate a drive control signal Sd. The excitation mode designation unit 124 determines the excitation mode for each phase based on the comparison results ScMa and Scmb by the comparison unit 121.

Here, the excitation mode will be described.
The excitation mode is an operation mode that specifies the excitation state of the coil 21. The motor drive control device 10 according to the embodiment has a charge mode and a decay mode as the excitation mode.

First, the charge mode will be described.
The charge mode is an operation mode in which the coil current is increased.

Figure 4A is a diagram to explain the charge mode.

In this embodiment, the configuration of the inverter circuit 143a for driving the A-phase coil 21a and the configuration of the inverter circuit 143b for driving the B-phase coil 21b are the same, so the excitation mode will be explained using the inverter circuit 143a for driving the A-phase coil 21a as an example.

As shown in FIG. 4A, the coils 21 of each phase of the motor 20 are connected to an inverter circuit 143 (H-bridge circuit). For example, the inverter circuit 143a has transistors Q1 to Q4 as switches and diodes D1 to D4.

Transistor Q1 and transistor Q2 are connected in series between the power supply voltage VDD and the ground potential via a shunt resistor serving as a current sensor 144a. Similarly, transistor Q3 and transistor Q4 are connected in series between the power supply voltage VDD and the ground potential via a shunt resistor serving as a current sensor 144a. The node where transistor Q1 and transistor Q2 are commonly connected is connected to the negative terminal AN of coil 21a (or BN of coil 21b), and the node where transistor Q3 and transistor Q4 are commonly connected is connected to the positive terminal AP of coil 21a (or BP of coil 21b).

The anode of diode D1 is connected to the node where transistors Q1 and Q2 are commonly connected, and the cathode of diode D1 is connected to the power supply voltage VDD. The anode of diode D2 is connected to ground potential GND, and the cathode of diode D2 is connected to the node where transistors Q1 and Q2 are commonly connected.

The anode of diode D3 is connected to the node where transistors Q3 and Q4 are commonly connected, and the cathode of diode D3 is connected to the power supply voltage VDD. The anode of diode D4 is connected to ground potential GND, and the cathode of diode D4 is connected to the node where transistors Q3 and Q4 are commonly connected.

Diodes D1 to D4 may be, for example, parasitic diodes of transistors Q1 to Q4, or may be realized by electronic components provided separately from transistors Q1 to Q4.

In the charge mode, the coil 21 is connected between the power supply voltage VDD and the ground potential GND, and is excited in the positive or negative direction. For example, as shown in FIG. 4A, by turning off the transistors Q1 and Q4 and turning on the transistors Q2 and Q3, a current flows from the positive terminal AP side of the coil 21a to the negative terminal AN side of the coil 21a, and the coil 21a is excited in the positive direction. On the other hand, by turning off the transistors Q2 and Q3 and turning on the transistors Q1 and Q4, a current flows from the negative terminal AN side of the coil 21a to the positive terminal AP side of the coil 21a, and the coil 21a is excited in the negative direction.

Next, the attenuation mode will be described.
The decay mode is an operation mode in which the coil current of the coil 21 is decayed. In the embodiment, the decay mode includes a slow decay mode in which the coil current is regenerated, a fast decay mode in which the coil current is regenerated faster than in the slow decay mode, and a mixed decay mode in which the coil current is regenerated by combining the slow decay mode and the fast decay mode.

FIG. 4B is a diagram for explaining the slow decay mode.
For example, when the current of the coil 21a excited in the positive direction by the charge mode is to be attenuated, the transistors Q1 and Q3 in the inverter circuit 143a are turned off and the transistors Q2 and Q4 are turned on by the slow decay mode. This allows the current of the coil 21a to be regenerated to the ground potential GND side and attenuated as shown in Fig. 4B. Similarly, when the current of the coil 21a excited in the negative direction is to be attenuated, the transistors Q1 and Q3 are turned off and the transistors Q2 and Q4 are turned on by the decay mode, allowing the current of the coil 21a to be regenerated to the ground potential GND side and attenuated.

FIG. 4C is a diagram for explaining the fast decay mode.
For example, when the current of the coil 21a excited in the positive direction in the charge mode is to be decayed, the transistors Q2 and Q3 in the inverter circuit 143a are turned off and the transistors Q1 and Q4 are turned on in the fast decay mode. This allows the current of the coil 21a to be regenerated to the power supply voltage VDD side, as shown in Fig. 4C. At this time, the coil 21a is excited in the opposite direction (negative) to the previous excitation direction (positive), so that the current of the coil 21a can be decayed faster than in the slow decay mode.

When the current in coil 21a, which has been excited in the negative direction, is to be decayed, the transistors Q1 and Q4 in inverter circuit 143a are turned off and the transistors Q2 and Q3 are turned on in the fast decay mode. This allows the current in coil 21a to be regenerated to the power supply voltage VDD side. At this time, coil 21a is excited in the opposite direction (positive) to the previous excitation direction (negative), so the current in coil 21a can be decayed faster than in the slow decay mode.

The PWM signal generating unit 128 generates the drive control signal Sd based on the excitation mode specified by the excitation mode specifying unit 124.

For example, when a charge mode is specified in which coil 21 is excited in the positive direction, the PWM signal generating unit 128 generates a drive control signal Sd that turns on transistors Q2 and Q3 and turns off transistors Q1 and Q4, as shown in FIG. 4A.

On the other hand, when the slow decay mode is specified after the coil 21 is excited in the positive direction, the PWM signal generating unit 128 generates a drive control signal Sd that turns on the transistors Q2 and Q4 and turns off the transistors Q1 and Q3, as shown in FIG. 4B. When the fast decay mode is specified after the coil 21 is excited in the positive direction, the PWM signal generating unit 128 generates a drive control signal Sd that turns on the transistors Q1 and Q4 and turns off the transistors Q2 and Q3, as shown in FIG. 4C.

When the coil 21 is excited in the negative direction, the PWM signal generating unit 128 generates the drive control signals Sda and Sdb according to the specified excitation mode so that the current flows in the opposite direction to the case of the negative excitation described above.

The excitation mode is specified by the excitation mode specifying unit 124 .
Specifically, the excitation mode designation unit 124 determines the excitation mode for each PWM period based on the comparison result Scm by the comparison unit 121. For example, the excitation mode designation unit 124 outputs excitation mode designation information Sma that designates the excitation mode of the A-phase coil 21a based on the comparison result of the comparison unit 121 between the measurement value Sia of the coil current Ia and the current reference value Sisa at the timing when one PWM period of the A phase is started. Also, the excitation mode designation unit 124 outputs excitation mode designation information Smb that designates the excitation mode of the B-phase coil 21b based on the comparison result of the comparison unit 121 between the measurement value Sib of the coil current Ib and the current reference value Sisb at the timing when one PWM period of the B phase is started.

When the excitation mode designation information Sma and the excitation mode designation information Smb are not distinguished from each other, the excitation mode designation information Sma and the excitation mode designation information Smb are written as "excitation mode designation information Sm."

When the comparison result of the comparator 121 is the first logic level (high level), i.e., when the measured coil current value Si is lower than the current reference value Sis, the excitation mode designation unit 124 outputs excitation mode designation information Sm that designates the charge mode as the excitation mode.

On the other hand, when the comparison result of the comparison unit 121 is the second logic level (low level), that is, when the measured coil current value Si is equal to or greater than the current reference value Sis, the excitation mode designation unit 124 outputs excitation mode designation information Sm that designates the damping mode as the excitation mode.

For example, when one PWM cycle is started, the measured current value Si is compared with the current reference value Sis, and if the measured current value Si does not reach the current reference value Sis (Si<Sis), the excitation mode designation unit 124 designates the charge mode as the excitation mode. If the measured current value Si reaches the current reference value Sis within that PWM cycle, the excitation mode designation unit 124 switches the excitation mode from the charge mode to the decay mode and maintains the decay mode until the end of that PWM cycle.

Here, the motor drive control device 10 may have a function of changing the excitation mode to the charge mode at least once in each PWM cycle. For example, the motor drive control device 10 may be set with a minimum time Tmin that specifies the minimum value of the length of the charge mode period in each PWM cycle. The information on the minimum time Tmin is set in advance in the storage unit 123, for example.

For example, even if the measured current value Si has already reached the current reference value Sis (Si≧Sis) at the timing when one PWM cycle is started, the excitation mode designation unit 124 outputs excitation mode designation information Sm that designates the charge mode as the excitation mode for at least the period equivalent to the minimum time Tmin, regardless of the comparison result of the comparison unit 121.

For example, after the start of one PWM cycle, the excitation mode designation unit 124 first designates the charge mode as the excitation mode. After designating the charge mode, the excitation mode designation unit 124 measures the period Ton of the charge mode, and when the period Ton reaches the minimum time Tmin, switches the excitation mode from the charge mode to the decay mode. Thereafter, the excitation mode designation unit 124 maintains the decay mode until the end of the PWM cycle.

When the charge mode is specified as the excitation mode, even if the measured current value Si reaches the current reference value Sis (the comparison result Scm becomes the second logic level (low level)) before the charge mode period reaches the minimum time Tmin, the excitation mode specification unit 124 continues the charge mode until the charge mode period Ton reaches the minimum time Tmin.

In this way, the excitation mode is charge mode for at least the period corresponding to the minimum time Tmin within each PWM cycle.

Here, the minimum time Tmin of the length of the charge mode period in the PWM cycle is, for example, a time equivalent to 10% or less of the PWM cycle, and preferably a time equivalent to 7.5% of the PWM cycle.

The PWM signal generating unit 128 outputs a drive control signal Sd that indicates the on/off pattern of the above-mentioned transistors Q1 to Q4 so that the coils 21a and 21b of each phase are in an excitation state corresponding to the specified excitation mode according to the excitation mode specified by the excitation mode specifying unit 124.

Figure 5 is a timing chart showing the changes over time in the motor coil current and the drive control signal.

The waveforms of the coil current Ia of coil 21a of phase A and the voltage (coil voltage) of coil 21a are shown from top to bottom on the page of Figure 5.

In the motor drive control device 10 according to the embodiment, the current reference value setting unit 122 alternates between a current increase period TI during which the current reference value Sis increases in a positive or negative direction and a current decay period TD during which the current reference value Sis changes toward zero for each coil 21a, 21b (each phase) to be driven. Then, as described above, the excitation mode designation unit 124 designates an excitation mode such that the measured current value Si does not exceed the current reference value Sis, and the PWM signal generation unit 128 generates drive control signals Sda, Sdb corresponding to the designated excitation mode. As a result, the coil currents Ia, Ib of each phase are controlled to have a sinusoidal shape, as shown in FIG. 5.

In addition, FIG. 5 shows, as an example, the phase of the current Ia in the A-phase coil 21a. If the motor 20 is a two-phase stepping motor having an A-phase coil and a B-phase coil, the phase of the current Ib in the B-phase coil 21b (not shown) is detected as being 90 degrees out of phase with the current Ia in the A-phase coil 21a.

As described above, the excitation mode designation unit 124 switches the excitation mode based on the comparison result between the measured coil current value Si and the current reference value Sis for each PWM period during the current increase period TI and the current decay period TD using the method described above.

On the other hand, the excitation mode designation unit 124 may differentiate the decay mode in the current increase period TI from the decay mode in the current decay period TD. For example, in the motor drive control device 10 according to this embodiment, the excitation mode designation unit 124 selects the slow decay mode as the decay mode in the current increase period TI. That is, in the current increase period TI, the charge mode or the slow decay mode is selected as the excitation mode. In addition, the excitation mode designation unit 124 selects the mixed decay mode as the decay mode in the current decay period TD. That is, in the current decay period TD, the charge mode or the mixed decay mode is selected as the excitation mode. The decay mode in the current decay period TD will be described in detail below.

Figure 6 is an enlarged view of a portion of the current decay period TD in Figure 5.

As shown in FIG. 6, the current decay period TD during which the current of the coil 21 (current reference value Sis) changes toward zero includes a first decay period Td1 and a second decay period Td2. The first decay period Td1 is the first predetermined period in the current decay period TD. The second decay period Td2 is the remaining predetermined period (Td2=TD-Td1) after the first decay period Td1 in the current decay period TD.

The lengths of the first decay period Td1 and the second decay period Td2 are, for example, set in advance. For example, the period when the electrical angle θ is from 90° to 120° (270° to 300°) is set as the first decay period Td1, and the period when the electrical angle θ is from 120° to 180° (300° to 360°) is set as the second decay period Td2.

The excitation mode designation unit 124 selects the slow decay mode as the decay mode for the first decay period Td1, and selects the mixed decay mode as the decay mode for the second decay period Td2.

Figure 7 shows an example of the change in coil current over time during the first decay period Td1.

In the figure, the horizontal axis represents time t, and the vertical axis represents current. Reference numeral 500 represents the change over time in the current of coil 21 (measured value Si of the current of coil 21). FIG. 7 also shows a case in which the current reference value Sis is set to "Ith2" in the first PWM period from time t0 to time t2, and the current reference value Sis is set to "Ith1 (<Ith2)" in the PWM periods after time t2.

As shown in FIG. 7, at time t0 when one PWM cycle starts, the excitation mode designation unit 124 compares the measured current value Si with the current reference value Sis (=Ith2). At this time, since the measured current value Si of the coil 21 has not reached the current reference value Sis (=Ith2), the excitation mode designation unit 124 sets the excitation mode to the charge mode (see FIG. 4A). This increases the current of the coil 21.

After that, when the measured current value Si reaches the current reference value Sis (=Ith2) at time t1, the excitation mode designation unit 124 switches the excitation mode from the charge mode to the slow decay mode (decay mode) and maintains the slow decay mode until time t2 when the next PWM cycle starts.

Then, at time t2 when a new PWM cycle starts, the excitation mode designation unit 124 compares the measured current value Si with the current reference value Si (=Ith1). As shown in FIG. 7, at time t2, the measured current value Si is higher than the current reference value Si (=Ith1), so the excitation mode designation unit 124 continues to set the excitation mode to the slow decay mode and maintains the slow decay mode until time t3 when the next PWM cycle starts.

In this way, in the first decay period Td1 in the current decay period TD, the slow decay mode is selected as the decay mode.

Figure 8 shows an example of the change in coil current over time during the second decay period Td2.

In FIG. 8, the horizontal axis represents time t, and the vertical axis represents current. Reference numeral 501 represents the change over time in the current of coil 21 (measured value Si of the current of coil 21). FIG. 8 also shows a case in which the current reference value Sis is set to "Ith2" in the first PWM period from time t0 to time t2, and the current reference value Sis is set to "Ith1 (<Ith2)" and "Ith0 (<Ith1)" in the PWM periods after time t2.

As shown in FIG. 8, the excitation mode designation unit 124 selects the mixed decay mode as the decay mode for the remaining second decay period Td2 of the current decay period TD.

Specifically, when the coil current is decayed in the mixed decay mode, the excitation mode designation unit 124 first designates one of the slow decay mode and the fast decay motor during the decay period Tdd in which the coil current is decayed within one PWM cycle, and then designates the other of the slow decay mode and the fast decay motor. For example, FIG. 8 illustrates a case in which the slow decay mode is designated first and then the fast decay mode is designated during the decay period Tdd of each PWM cycle. FIG. 8 also illustrates a case in which the slow decay mode and the fast decay mode are designated once each during the decay period Tdd.

When one PWM cycle starts, the excitation mode designation unit 124 designates the charge mode as the excitation mode and starts measuring the length of the charge mode period Ton. Then, when the excitation mode designation unit 124 detects that the measured value Si of the current of the coil 21 has reached the current reference value Sis and that the measured time of the charge mode period Ton is equal to or longer than the minimum time Tmin, it switches the excitation mode from the charge mode to the decay mode.

For example, as shown in FIG. 8, at time t0 when the PWM cycle starts, the excitation mode designation unit 124 first sets the excitation mode to the charge mode and starts measuring time to measure the length of the charge mode period Ton. This causes the current in the coil 21 to increase (see FIG. 4A).

After that, at time t1 when the measured current value Si reaches the current reference value Sis (=Ith2) and the measured time of the charge mode period Ton is detected to be equal to or longer than the minimum time Tmin set in the memory unit 123, the excitation mode designation unit 124 switches the excitation mode from the charge mode to the slow decay mode. As a result, the current in the coil 21 decreases at a constant rate, as shown in FIG. 8 (see FIG. 4B).

Here, the period T1 of the slow decay mode is determined by the specified time Tf1 that specifies the length of the period T1 of the slow decay mode stored in the memory unit 123. For example, when the PWM period is T, the period of the charge mode is Ton, the decay period is Tdd, and the specified time that specifies the length of the period T2 of the fast decay mode is Tf2, the specified time Tf1 that specifies the length of the period T1 of the slow decay mode is expressed by the following formula (1).

For example, when the charge mode ends, the excitation mode designation unit 124 updates the designated time Tf1 based on the above formula (1) and sets the excitation mode to the slow decay mode. Then, after setting the excitation mode to the slow decay mode, the excitation mode designation unit 124 starts measuring the length of the period T1 of the slow decay mode.

After that, at time tc1 when the measurement time of the period T1 of the slow decay mode reaches the specified time Tf1, the excitation mode designation unit 124 switches the excitation mode from the slow decay mode to the fast decay mode, and maintains the fast decay mode until time t2 when the next PWM cycle starts. As a result, the fast decay mode continues for a period equivalent to the specified time Tf2, and the current in the coil 21 decreases at a steeper slope than in the slow decay mode (see FIG. 4C).

Similarly, after time t2 in Figure 8, the excitation mode is switched between the charge mode and the mixed decay mode every PWM period.

Here, when the coil current is decayed in the mixed decay mode, the proportion of the fast decay mode period T2 in the decay period Tdd within one PWM cycle is dynamically changed.

Specifically, when the excitation mode designation unit 124 detects that the measured value Si of the coil current has reached the current reference value Sis in the mixed decay mode, it performs an increase process to make the proportion (T2/Tdd) of the period T2 of the fast decay mode in the decay period Tdd in the PWM cycle greater than the proportion of the period T2 of the fast decay mode in the decay period Tdd in the previous PWM cycle.

For example, when the excitation mode designation unit 124 detects that the charge mode period Ton in the PWM cycle matches the minimum time Tmin (Ton = Tmin), it performs an increase process.

The fact that the charge mode period Ton in the PWM cycle coincides with the minimum time Tmin indicates that the coil current (the measured coil current value Si) has already reached the current reference value Sis before the minimum time Tmin has elapsed. In other words, in this case, since sufficient coil current is supplied to generate the torque required by the motor, the coil current needs to decay quickly in the current decay period TD for changing the coil current into a sinusoidal wave. Therefore, it is preferable to extend the period of the fast decay mode in the mixed decay mode.

When the excitation mode designation unit 124 detects that the charge mode period is the minimum time Tmin, it determines that the coil current has already reached the current reference value Sis, and performs an increase process to make the proportion of the period T2 of the fast decay mode in the decay period Tdd in the PWM cycle greater than the proportion of the period T2 of the fast decay mode in the decay period Tdd in the previous PWM cycle.

More specifically, each time the excitation mode specifying unit 124 detects that the measured coil current value Si has reached the current reference value Sis, it increases the period T2 of the fast decay mode in the decay period Tdd within the PWM cycle by a unit increase time ΔT.

The unit increase time ΔT is information that specifies the amount of increase in the period of the fast decay mode, and is stored, for example, in the memory unit 123. The unit increase time ΔT can be set appropriately depending on the application to which the actuator 1 is applied. For example, it is preferable that the unit increase time ΔT is a time equivalent to 10% or less of the PWM period.

Here, an upper limit time Tlmt may be set to specify an upper limit value for the length of the period T2 of the fast decay mode. For example, each time the excitation mode specifying unit 124 detects that the measured value Si of the coil current has reached the current reference value Sis, it increases the period of the fast decay mode in the decay period Tdd within the PWM cycle by a unit increase time ΔT up to the upper limit time Tlmt.

The information on the upper limit time Tlmt is stored, for example, in the memory unit 123. The upper limit time Tlmt can be set appropriately depending on the application to which the actuator 1 is applied. For example, when the PWM period is T and the minimum time is Tmin, Tlmt≦(T-Tmin).

Here, we will explain the flow of the increase process that increases the period of fast decay mode in mixed decay mode.

Figure 9 is a flowchart showing an example of the flow of an increase process for increasing the period of the fast decay mode in the mixed decay mode.

For example, when a new PWM cycle starts, the excitation mode specification unit 124 determines whether the charge mode period Ton in the immediately preceding PWM cycle matches the minimum time Tmin (step S1).

If the charge mode period Ton does not match the minimum time Tmin (step S1: NO), the excitation mode designation unit 124 does not execute the increase process, but instead switches the excitation mode based on the comparison result between the coil current and the current reference value using the method described above.

On the other hand, if the period Ton of the charge mode matches the minimum time Tmin (step S1: YES), the excitation mode designation unit 124 starts the increase process. First, the excitation mode designation unit 124 acquires a designated time Tf2 that designates the length of the period T2 of the fast decay mode (step S2). For example, the designated time Tf2 of the fast decay mode is stored in the memory unit 123. The excitation mode designation unit 124 reads out the designated time Tf2 from the memory unit 123.

Next, the excitation mode designation unit 124 adds the unit increase time ΔT (e.g., a time equivalent to 10% of the PWM period) read from the storage unit 123 to the designated time Tf2 of the high-speed decay mode read in step S2 (step S3). As a result, the excitation mode designation unit 124 obtains a sum (Tf2+ΔT) by adding ΔT to Tf2.

Next, the excitation mode designation unit 124 determines whether the added value (Tf2+ΔT) is equal to or greater than the upper limit time Tlmt stored in the memory unit 123 (step S4). If the added value (Tf2+ΔT) is smaller than the upper limit time Tlmt (step S4: NO), the excitation mode designation unit 124 updates the designated time Tf2 of the fast decay mode stored in the memory unit 123 to the added value (Tf2+ΔT) (step S5). As a result, the designated time Tf2 of the fast decay mode becomes (Tf2+ΔT), and the increase process ends.

On the other hand, if the added value (Tf2+ΔT) is equal to or greater than the upper limit time Tlmt (step S4: YES), the excitation mode designation unit 124 updates the designated time Tf2 of the fast decay mode stored in the storage unit 123 to the upper limit time Tlmt (step S6). As a result, the designated time Tf2 of the fast decay mode becomes Tlmt, and the increase process ends.

The above steps are used to increase the period of fast decay mode.

Next, the process of increasing the period of the fast decay mode will be described with reference to FIG.
For example, when a new PWM cycle (a PWM cycle from time t2 to time t4) starts at time t2 in FIG. 8, the excitation mode designation unit 124 compares the period Ton of the charge mode in the previous PWM cycle with the minimum time Tmin. As shown in FIG. 8, the period Ton of the charge mode in the previous PWM cycle, i.e., the PWM cycle from time t0 to time t2, is longer than the minimum time Tmin. Therefore, the excitation mode designation unit 124 does not perform the above-mentioned increase process. Then, in the PWM cycle from time t2 to time t4, the excitation mode designation unit 124 switches the excitation mode based on the comparison result Scm by the above-mentioned method.

After that, when a new PWM cycle (a PWM cycle from time t4 to time t6) starts at time t4, the excitation mode designation unit 124 compares the charge mode period Ton in the previous PWM cycle with the minimum time Tmin. As shown in FIG. 8, the charge mode period Ton in the previous PWM cycle, i.e., the PWM cycle from time t2 to time t4, matches the minimum time Tmin. Therefore, the excitation mode designation unit 124 performs an increase process. That is, the excitation mode designation unit 124 sets the sum (Tf2+ΔT) obtained by adding the unit increase time ΔT to the designated time Tf2 of the fast decay mode stored in the memory unit 123 as the new designated time (<Tlmt) of the fast decay mode in the memory unit 123. As a result, as shown in FIG. 8, the period T2 of the fast decay mode in the PWM cycle from time t4 to time t6 is longer by ΔT than the period T2 of the fast decay mode in the previous PWM cycle from time t2 to time t4.

In this way, the motor drive control device 10 dynamically changes the period T2 of the fast decay mode in the mixed decay mode for each PWM period.

In the above example, the increase process is performed at the timing when one PWM cycle starts, but the increase process may be performed every PWM cycle or every several PWM cycles, and there is no particular limitation on the timing when the increase process starts.

Next, we will explain the effects of the motor drive control device 10 according to the embodiment.

Figure 10A shows the results of measuring the coil current when a motor is driven by a motor drive control device according to a prior study by the present inventors as a comparative example.

Figure 10B shows the actual measurement results of the coil current when the motor is driven by the motor drive control device 10 according to the embodiment.

Figures 10A and 10B show the waveforms of the coil current Ia of the motor's phase A, respectively.

The motor drive control device according to the prior study example differs from the motor drive control device 10 according to the embodiment in that the period of the high-speed decay mode in the mixed decay mode is fixed, but in other respects it is similar to the motor drive control device 10 according to the embodiment.

As shown in FIG. 10A, with the motor drive control device according to the prior study example, the coil current may not be sufficiently attenuated during the current decay period (corresponding to the current decay period TD(+) in FIG. 5), and the coil current may not be changed to a sinusoidal wave.

In contrast, the motor drive control device 10 according to the embodiment dynamically changes the period of the fast decay mode in the mixed decay mode according to the magnitude relationship between the coil current and the current reference value. That is, when the motor drive control device 10 detects that the coil current has reached the current reference value in the mixed decay mode, it performs an increase process to increase the proportion of the period T2 of the fast decay mode in the decay period Tdd in the PWM cycle to be greater than the proportion of the period T2 of the fast decay mode in the decay period Tdd in the previous PWM cycle.

As a result, as shown in FIG. 10B, the coil current can be sufficiently attenuated during the current attenuation period for changing the coil current into a sinusoidal wave, making it possible to make the coil current waveform closer to a sine wave.

In addition, according to the motor drive control device 10 of the embodiment, the mixed decay mode can generate gradual decay and steep decay of the coil current. This can reduce the change in current caused by switching the decay mode during the current decay period TD, thereby reducing distortion of the sinusoidal coil current and making it possible to suppress the generation of abnormal noise when the motor is driven.

In this way, the motor drive control device 10 according to the embodiment makes it possible to appropriately control the motor coil current while suppressing the generation of abnormal noise when the motor is driven.

In addition, as described above, the motor drive control device 10 according to the embodiment performs an increase process when it detects that the charge mode period Ton in the PWM cycle matches the minimum time Tmin that specifies the minimum value of the length of the charge mode period Ton.
This makes it possible to easily detect whether or not the coil current has reached the current reference value.

Furthermore, a unit increase time ΔT that specifies the amount of increase in the period of the fast decay mode is set in the motor drive control device 10 according to the embodiment. The motor drive control device 10 performs the increase process for each PWM period, and in the increase process, increases the period of the fast decay mode in the decay period Tdd within the PWM period by the unit increase time ΔT.
According to this, the ratio of the period T2 of the fast decay mode in the decay period Tdd within the PWM period can be gradually increased for each PWM period, thereby realizing stable motor drive control. Also, by setting the unit increase time ΔT to an appropriate value according to the application to which the actuator 1 is applied, stable motor drive control can be realized for each application.

Furthermore, an upper limit time Tlmt indicating an upper limit of the length of the period of the fast decay mode is set in the motor drive control device 10 according to the embodiment. The motor drive control device 10 increases the period T2 of the fast decay mode in the decay period Tdd within the PWM cycle by unit increase time ΔT up to the upper limit time Tlmt by performing an increase process every time it detects that the coil current has reached the current reference value.
According to this, by setting an appropriate upper limit value for the period T2 of the fast decay mode depending on the application to which the actuator 1 is applied, it is possible to realize stable motor drive control for each application.

<<Extension of the embodiment>>
The invention made by the present inventors 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, when the coil current is decayed in the mixed decay mode, an example is shown in FIG. 8 in which the slow decay mode is specified at the beginning of the decay period Tdd of each PWM cycle, and then the fast decay mode is specified, but the order of the decay modes specified in the mixed decay mode is not particularly limited. For example, in the decay period Tdd, the fast decay mode may be specified first, and then the slow decay mode may be specified.

In addition, FIG. 8 illustrates an example in which the slow decay mode and the fast decay mode are each specified once during the decay period Tdd in one PWM cycle, but the number of times the slow decay mode and the fast decay mode are specified during the decay period Tdd is not particularly limited. For example, the slow decay mode and the fast decay mode may be alternately repeated multiple times during the decay period Tdd.

In addition, in the above embodiment, the number of phases of the motor 20 is not limited to two. Also, the motor 20 in the above embodiment is not limited to a stepping motor. For example, the motor 20 may be a brushless DC motor.

The above-mentioned flowchart shows an example for explaining the operation, and is not limited to this. In other words, the steps shown in each figure of the flowchart are specific examples, and are not limited to this flow. For example, the order of some of the processes may be changed, other processes may be inserted between each process, and some processes may be performed in parallel.

1...actuator, 10...motor drive control device, 12...control circuit, 14...drive circuit, 20...motor (stepping motor), 21, 21a, 21b...coil, 22...rotor, 22n...north pole, 22s...south pole, 25...output shaft, 26...primary gear, 29...motor terminal, 31...secondary gear (power transmission mechanism), 32...tertiary gear (power transmission mechanism), 33...output gear (power transmission mechanism), 42...printed circuit board, 43...flexible printed circuit board, 51...case, 52...cover, 120...current value acquisition unit, 121...comparison unit, 122...current reference value setting unit, 123...storage unit, 124...excitation mode designation unit, 126...drive control signal generation unit, 127...drive command acquisition unit, 128...PWM signal generation unit, 143, 143a, 143b...inverter circuit ( H-bridge circuit), 144a, 144b...current sensor, AP, BP...positive terminal of coil 21, AN, BN...negative terminal of coil 21, Q1 to Q4...transistor, D1 to D4...diode, Ia, Ib...coil current, Scm, Scma, Scmb...comparison result, Sd, Sda, Sdb...drive control signal, Si, Sia, Sib...measured coil current, Sis, Sis1, Sis2...current reference value, T1...slow decay mode period, T2...fast decay mode period, Tdd...decay period within PWM cycle, Tf1...specified time for slow decay mode period, Tf2...specified time for fast decay mode period, ΔT...unit increase time, Tlmt...upper limit time, Tmin...minimum time, Ton...charge mode period, Via, Vib...current detection signal.

Claims (7)

a control circuit that generates a drive control signal for controlling the drive of the motor;
a drive circuit for exciting a coil of the motor based on the drive control signal;
The control circuit includes:
a current value acquisition unit for acquiring a measurement value of a coil current which is a current flowing through the coil;
a drive control signal generating unit that generates a PWM signal so that the coil is in a state corresponding to a specified excitation mode, and outputs the PWM signal as the drive control signal;
a current reference value setting unit that sets a current reference value that is a reference for the coil current for each PWM period of the PWM signal so that the current flowing through the coil changes in a sinusoidal shape;
an excitation mode designation unit that, when a measured value of the coil current measured by the current value acquisition unit is lower than the current reference value, designates a charge mode in which the coil current is increased as the excitation mode, and, when the measured value of the coil current is equal to or higher than the current reference value, designates a decay mode in which the coil current is decreased as the excitation mode,
the decay modes include a slow decay mode in which the coil current is regenerated, a fast decay mode in which the coil current is regenerated faster than in the slow decay mode, and a mixed decay mode in which the coil current is regenerated by combining the slow decay mode and the fast decay mode;
the excitation mode designation unit, when attenuating the coil current in the mixed decay mode, first designates one of the slow decay mode and the fast decay mode, and then designates the other of the slow decay mode and the fast decay mode, during a decay period in which the coil current is attenuated within one of the PWM cycles;
when detecting that the coil current has reached the current reference value in the mixed decay mode, the excitation mode designation unit performs an increasing process to make a proportion of the period of the fast decay mode in the decay period within the PWM cycle greater than a proportion of the period of the fast decay mode in the decay period in the previous PWM cycle. 2. The motor drive control device according to claim 1,
a storage unit that stores a minimum time that specifies a minimum value of a length of the period of the charge mode in the PWM cycle;
The motor drive control device, wherein the excitation mode designation unit performs the increasing process when it detects that the period of the charge mode in the PWM cycle is the minimum time. 3. The motor drive control device according to claim 2,
the excitation mode designation unit performs the increasing process for each PWM period,
The storage unit stores a unit increase time that specifies an increase amount of a period of the fast decay mode,
The motor drive control device, wherein the excitation mode designation unit increases a period of the high speed decay mode in the decay period within the PWM cycle by the unit increase time in the increasing process. 4. The motor drive control device according to claim 3,
The storage unit stores an upper limit time indicating an upper limit value of a length of a period of the fast decay mode,
the excitation mode designation unit increases a period of the high speed decay mode in the decay period within the PWM cycle by the unit increase time up to the upper limit time every time it detects that the coil current has reached the current reference value. 5. The motor drive control device according to claim 4,
the excitation mode designation unit designates the slow decay mode as the decay mode for a first decay period, which is a first period in a current decay period in which the current reference value changes toward zero, and designates the mixed decay mode as the decay mode for a second decay period, which is a remaining period after the first decay period in the current decay period. The motor;
A motor drive control device according to any one of claims 1 to 5,
and a power transmission mechanism that transmits the rotational force of the motor to a driven object. A motor drive control method for controlling the drive of a motor by a motor drive control device, comprising:
a first step in which the motor drive control device generates a PWM signal so that a coil of the motor is in an excitation state according to a specified excitation mode, and drives the motor based on the PWM signal;
a second step of the motor drive control device setting a current reference value that is a reference for the coil current, which is a current flowing through the coil, for each PWM period of the PWM signal so that the coil current has a sine wave shape;
a third step in which the motor drive control device, when a measured value of the coil current is lower than the current reference value, specifies a charge mode in which the coil current is increased as the excitation mode, and when a measured value of the coil current is equal to or higher than the current reference value, specifies a decay mode in which the coil current is decreased as the excitation mode,
the decay modes include a slow decay mode in which the coil current is regenerated, a fast decay mode in which the coil current is regenerated faster than in the slow decay mode, and a mixed decay mode in which the coil current is regenerated by combining the slow decay mode and the fast decay mode;
The third step is
a fourth step of, when the motor drive control device decays the coil current in the mixed decay mode, first designating one of the slow decay mode and the fast decay mode, and then designating the other of the slow decay mode and the fast decay mode, during a decay period in which the coil current is decayed within one of the PWM cycles;
and a fifth step of performing, when the motor drive control device detects that the coil current has reached the current reference value in the mixed decay mode, an increasing process of making a ratio of a period of the fast decay mode in the decay period in the PWM cycle larger than a ratio of a period of the fast decay mode in the decay period in the previous PWM cycle.
A motor drive control method.

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