Motor drive control device, actuator, and motor drive control method

Abstract

To suppress generation of an allophone when driving a stepping motor.SOLUTION: In a motor controller 10, a control unit 122 compares a measurement value Si of current of a coil 21 with a current reference value Sis for every PWM period, designates a charge mode as an exciting mode when the measurement value Si of the current does not reach the current reference value Sis and designates an attenuation mode as the exciting mode when the measurement value Si of the current reaches the current reference value Sis. The control unit 122 designates a low-speed attenuation mode as the attenuation mode in a first attenuation period Td1 in a current attenuation period TD and designates a mixed attenuation mode for alternately switching the low-speed attenuation mode and a high-speed attenuation mode as the attenuation mode in a second attenuation period Td2 in the current attenuation period TD (refer to Fig. 9). The control unit 122 generates a drive control signal Sd according to the designated excitation mode to control drive of a motor 20.SELECTED DRAWING: Figure 4

Description

Technical Field

[0001] 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.

Background Art

[0002] Conventionally, as a method for driving and controlling motors such as stepping motors and brushless DC motors, a method of driving a coil so that the current flowing through the coil of the motor becomes a sine wave is known.

[0003] For example, in the microstep method, which is one of the driving methods of a stepping motor, a motor drive control device changes the reference value (command value) of the current in a stepped manner so that the current in each phase coil constituting the stepping motor becomes a sine wave, monitors the current in the coil, and switches the excitation state of each phase coil so that the detected value of the current in the coil does not exceed the reference value.

[0004] Generally, in the microstep method, according to the electrical angle θ (position of the rotor) of the stepping motor, the period in which the current in the coil is increased in the positive or negative direction and the period in which the current in the coil is changed toward zero are alternately repeated, so that the current in the coil is controlled to be a sine wave.

[0005] Generally, when controlling the driving of a stepping motor by the microstep method, as a control method (excitation mode) for attenuating the current, a slow decay mode in which the current in the coil is regenerated and a fast decay mode in which the current is regenerated at a higher speed than the slow decay mode are known (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0006] [Patent Document 1] Japanese Patent Publication No. 2006-254542 [Overview of the project] [Problems that the invention aims to solve]

[0007] In conventional microstepping stepping motor drive methods, it is common practice to gradually reduce the coil current using a low-speed damping mode during the initial predetermined period of the damping phase in which the coil current is changed toward zero, and then to rapidly reduce the coil current using a high-speed damping mode during the subsequent period.

[0008] In the conventional drive method described above, when switching from the low-speed damping mode to the high-speed damping mode during the damping period, the amount of damping in the coil changes significantly. This change in the amount of damping in the current causes significant distortion in the coil current waveform, and this distortion may result in loud abnormal noises being generated from the stepping motor.

[0009] This invention has been made in view of the above-mentioned problems, and aims to suppress the generation of abnormal noise when a motor is driven. [Means for solving the problem]

[0010] A motor drive control device according to a typical embodiment of the present invention comprises a control circuit that generates a drive control signal for controlling the drive of a motor, and a drive circuit that excites the motor coil based on the drive control signal, wherein the control circuit includes a current value acquisition unit that acquires a measured value of the current of 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 it as the drive control signal, a current reference value setting unit that sets a current reference value for the current at each PWM period of the PWM signal so that the current flowing through the coil changes sinusoidally, and compares the measured value of the current measured by the current value acquisition unit with the current reference value at each PWM period, and if the measured value of the current has not reached the current reference value The device also includes an excitation mode designation unit that specifies a charge mode to increase the current as the excitation mode, and when the measured value of the current reaches the current reference value, it specifies a damping mode to decrease the current as the excitation mode, wherein the excitation mode designation unit specifies a low-speed damping mode to regenerate the current as the damping mode during a first damping period, which is the first period in the current damping period during which the current reference value changes toward zero, and specifies a mixed damping mode to alternately switch between the low-speed damping mode and a high-speed damping mode to regenerate the current at a faster speed than the low-speed damping mode as the damping mode during a second damping period, which is the remaining period after the first damping period in the current damping period. [Effects of the Invention]

[0011] According to the motor drive control device of the present invention, it is possible to suppress the generation of abnormal noise when the motor is driven. [Brief explanation of the drawing]

[0012] [Figure 1] This 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. [Figure 2] This is a schematic diagram showing the configuration of a motor. [Figure 3]It is a block diagram showing the configuration of a motor drive control device according to an embodiment. [Figure 4] It is a diagram showing the functional block configuration of a control circuit in a motor drive control device according to an embodiment. [Figure 5A] It is a diagram for explaining a charge mode. [Figure 5B] It is a diagram for explaining a low-speed attenuation mode. [Figure 5C] It is a diagram for explaining a high-speed attenuation mode. [Figure 6] It is an example of a timing chart showing the temporal change of the current in the coil of a motor and a drive control signal. [Figure 7] It is a diagram obtained by enlarging a part of the current decay period TD in FIG. 6. [Figure 8] It is a diagram showing an example of the temporal change of the current in the coil during the first decay period Td1. [Figure 9] It is a diagram showing an example of the temporal change of the current in the coil during the second decay period Td2. [Figure 10] It is a flowchart showing the flow of switching control of an excitation mode by a motor drive control device according to an embodiment. [Figure 11] It is a diagram showing the measured result of the current in the coil when driving a motor by a conventional motor drive control device as a comparative example. [Figure 12] It is a diagram showing the measured result of the current in the coil when driving a motor by a motor drive control device according to an embodiment. [Figure 13] It is a diagram showing another example of the temporal change of the current in the coil during the second decay period Td2.

Embodiments of the Invention

[0013] Hereinafter, specific examples of embodiments of the present invention will be described with reference to the drawings. In the following description, the same reference numerals are assigned to the common components in each embodiment, and the repeated description is omitted.

[0014] FIG. 1 is an exploded perspective view showing an example of the structure of an actuator equipped with a motor drive control device according to the present embodiment.

[0015] The actuator 1 is, for example, a device for driving an air conditioner in an HVAC (Heating Ventilation and Air-Conditioning) system as an in-vehicle air conditioning unit. Examples of the actuator 1 include various actuators that can be used in an HVAC system, such as a damper actuator, a valve actuator, a fan actuator, and a pump actuator.

[0016] In the HVAC system, the actuator 1 is connected to an ECU (not shown) as a higher-level device via a bus together with other actuators, for example, to form a LIN (Local Interconnect Network) communication network.

[0017] As shown in FIG. 1, the actuator 1 is covered with a case 51 and a cover 52. Inside the actuator 1, a motor 20, a motor drive control device 10 that controls the drive of the motor 20, and secondary gears 31, tertiary gears 32, and an output gear 33 as a power transmission mechanism that transmits the rotational force of the motor 20 to the drive target are housed.

[0018] The motor 20 generates the driving force of the actuator 1. The motor 20 is, for example, a stepping motor. In the present embodiment, the motor 20 will be described as a two-phase stepping motor having a phase A coil and a phase B coil. As will be described later, the motor 20 operates when drive power is supplied from the motor drive control device 10 to the coils of each phase.

[0019] FIG. 2 is a diagram schematically showing the configuration of the motor 20.

[0020] As described above, the motor 20 is a two-phase stepping motor. As shown in Figure 2, the motor 20 has a coil 21a for phase A, a coil 21b for phase B, a rotor 22, and a two-phase stator yoke (not shown).

[0021] Coils 21a and 21b are coils that excite the stator yoke (not shown), respectively. Coil 21a has a positive terminal AP and a negative terminal AN as motor terminals 29. Coil 21b has a positive terminal BP and a negative terminal BN as motor terminals 29. The positive terminal AP and negative terminal AN of coil 21a and the positive terminal BP and negative terminal BN of coil 21b are connected to inverter circuits (e.g., H-bridge circuits) 143a and 143b that constitute the motor drive unit 142. Details of inverter circuits 143a and 143b will be described later.

[0022] Coils 21a and 21b are driven by inverter circuits 143a and 143b. As a result, currents Ia and Ib with different phases flow through coils 21a and 21b. For example, currents Ia and Ib with a 90-degree phase difference flow through coils 21a and 21b.

[0023] In the following explanation, when coil 21a and coil 21b are not distinguished, they will simply be referred to as "coil 21".

[0024] The rotor 22 is equipped with a multi-pole magnetized permanent magnet such that the south pole 22S and north pole 22N alternately reverse direction along the circumferential direction. Figure 2 shows an example where the rotor 22 has two poles.

[0025] The stator yoke is positioned around the rotor 22, close to its outer circumference. The rotor 22 rotates due to the periodic switching of the phase of the coil current flowing through coils 21a and 21b. An output shaft 25 is connected to the rotor 22, and the rotational force of the rotor 22 drives the output shaft 25.

[0026] A primary gear 26 is attached to the output shaft 25 of the motor 20. As shown in Figure 1, the primary gear 26 of the motor 20 meshes with the secondary gear 31. The secondary gear 31 meshes with the tertiary gear 32. The tertiary gear 32 meshes with the 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 the drive target.

[0027] 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. Based on the drive command Sc, which is a control frame received from the higher-level device, the motor drive control device 10 controls the rotation and stopping of the motor 20 by controlling the energization state of the coils 21a and 21b of each phase of the motor 20, thereby controlling the operation of the entire actuator 1. 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 due to the rotation of the primary gear 26 is transmitted sequentially to the secondary gear 31, tertiary gear 32, output gear 33, and external output gear, and the external output gear drives the movable part of the air conditioning unit that is the target of the drive.

[0028] As shown in Figure 1, the motor drive control device 10 has, as hardware resources, 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 plurality of external connection terminals 41.

[0029] Note that the only circuit housed inside the case 51 and cover 52 is the drive circuit 14. For example, the motor drive control device 10 may consist of a drive circuit 14 provided inside the case 51 and cover 52 and a control circuit 12 provided outside the case 51 and cover 52.

[0030] Figure 3 is a block diagram showing the configuration of the motor drive control device 10 according to the embodiment.

[0031] As shown in Figure 3, the motor drive control device 10 includes a control circuit 12 and a drive circuit 14.

[0032] The control circuit 12 controls the rotation of the motor 20 by generating a drive control signal Sd to control the rotation of the motor 20 based on a drive command Sc from a higher-level device (ECU), and controlling the drive circuit 14.

[0033] The drive command Sc is a signal that indicates the target state of the motor 20. The drive command Sc includes, for example, information specifying the rotational speed of the motor 20, and information specifying the target rotation angle (target rotation position) of the motor 20. Further details about the control circuit 12 will be described later.

[0034] The drive circuit 14 controls the energization of the motor 20's coil 21 based on the drive control signal Sd output from the control circuit 12. The drive circuit 14 includes a motor drive unit 142 and a current sensor 144.

[0035] The motor drive unit 142 supplies drive power to the motor 20 based on the drive control signal Sd.

[0036] As shown in Figure 2, the motor drive unit 142 has, for example, inverter circuits 143a and 143b corresponding to each of the coils 21a and 21b to be driven. The inverter circuits 143a and 143b are, for example, H-bridge circuits. Hereafter, when inverter circuit 143a and inverter circuit 143b are not distinguished, they will be referred to as "inverter circuit 143".

[0037] As shown in Figure 2, 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. 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.

[0038] Inverter circuit 143a causes a current Ia to flow through coil 21a by applying a voltage Va between terminals AP and AN. Inverter circuit 143b causes a current Ib to flow through coil 21b by applying a voltage Vb between terminals BP and BN.

[0039] 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 to the negative terminal AN of the coil 21a, the voltage Va at the positive terminal AP relative to the negative terminal AN is set to "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 at the positive terminal AP relative to the negative terminal AN is set to "negative". The same applies when exciting the B-phase coil 21b.

[0040] The current sensor 144 detects the current (coil current) flowing through the coils 21 of each phase of the motor 20. The current sensor 144 includes, for example, a shunt resistor that converts the current flowing through the coils 21 into a voltage. As will be described in detail later, a shunt resistor is provided for each phase coil 21a, 21b and is connected in series with the inverter circuits 143a, 143b to the ground potential GND side or the power supply voltage VDD. The current sensor 144 outputs the voltage across the shunt resistor as the detection result of the currents Ia, Ib of each phase coil 21a, 21b and supplies it to the control circuit 12.

[0041] As shown in Figure 2, the control circuit 12 includes, for example, a control unit 122, a current measuring unit 124, and a back electromotive force measuring unit 126.

[0042] The current measurement unit 124 measures the currents Ia and Ib of the coils 21a and 21b of each phase of the motor 20. The current measurement unit 124 receives a voltage output from the current sensor 144 (shunt resistor) corresponding to the currents Ia and Ib of the coils 21a and 21b of each phase. Based on the input voltage, the current measurement unit 124 calculates the measured values ​​of the currents Ia and Ib of the coils 21a and 21b of each phase. For example, the current measurement unit 124 is configured to include an A / D conversion circuit.

[0043] For example, the current measurement unit 124 converts the voltage of the A-phase current sensor 144 (shunt resistor) into a digital value and outputs it as the measured value Sia of the current in the A-phase coil 21a. The current measurement unit 124 converts the voltage of the B-phase current sensor 144 (shunt resistor) into a digital value and outputs it as the measured value Sib of the current in the B-phase coil 21b.

[0044] The back electromotive force measurement unit 126 measures the back electromotive force induced in the coil 21 of the motor 20 that is not energized, among the coils 21 of the multiple phases 20. In this embodiment, the back electromotive force measurement unit 126 is connected to each of the four lines (positive terminals AP, BP and negative terminals BP, BN of the coils 21 of each phase) that connect the drive circuit 14 and the motor 20. The back electromotive force measurement unit 126 outputs the measured value of the back electromotive force, Sbef, to the control unit 122. The back electromotive force measurement unit 126 is configured to include, for example, a resistive voltage divider circuit and an A / D conversion circuit that converts the divided voltage into a digital signal.

[0045] The control unit 122 is a circuit for performing overall control of the control circuit 12. The control unit 122 is a program processing unit (e.g., a microcontroller: MCU) that includes hardware elements such as a processor (CPU: Central Processing Unit), various types of memory (ROM: Read Only Memory, RAM: Random Access Memory), timers, counters, A / D conversion circuits, input / output I / F circuits, and clock generation circuits, with each component connected to the others via a bus or dedicated line. The control unit 122 has a rewritable non-volatile storage device as memory, such as flash memory or EEPROM (Electrically Erasable Programmable Read-Only Memory).

[0046] Furthermore, some or all of the current measurement unit 124 and the back electromotive force measurement unit 126 described above may be implemented using an A / D conversion circuit or the like within the MCU that constitutes the control unit 122, or they may be implemented by a separate IC (Integrated Circuit) provided separately from the MCU.

[0047] The control unit 122 primarily has the 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 unit 122 generates a drive control signal Sd to drive the inverter circuit 143 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.

[0048] Here, the predetermined excitation method is, for example, one of the known single-phase excitation methods, two-phase excitation methods, one-to-two-phase excitation methods, and microstepping methods. In this embodiment, the case where the predetermined excitation method is a two-phase microstepping method will be used as an example for explanation.

[0049] The control unit 122 generates a drive control signal Sd using a two-phase microstepping method. Specifically, the control unit 122 changes the current reference value Sis, which is the current command, in a stepwise manner so that the currents Ia and Ib of the coils 21a and 21b of each phase constituting the motor 20 become sinusoidal. At the same time, it monitors the coil currents Ia and Ib and switches 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 value Sis. Specifically, the control unit 122 generates a PWM signal (drive control signal Sd) whose pulse width changes according to the relationship between the current of the coil 21 of the motor 20 and the current reference value Sis, and performs PWM control to control the drive of the motor 20 via the drive circuit 14.

[0050] Figure 4 is a diagram showing the functional block configuration of the control unit 122 in the motor drive control device according to the embodiment.

[0051] As shown in Figure 4, the control unit 122 includes, for example, a drive control signal generation unit 132, a current value acquisition unit 133, a current reference value setting unit 134, an excitation mode specification unit 135, and a storage unit 137 as functional blocks for realizing the above-described functions. These functional blocks are realized by the processor within the MCU, as described above, executing various calculations according to the program stored in memory, and controlling peripheral circuits such as timers and counters, A / D conversion circuits, and input / output I / F circuits.

[0052] In addition to the above functions, the control unit 122 may also have a function to determine whether or not the motor 20 has lost step based on the back electromotive force of the motor 20. In this case, the control unit 122 further includes a step-out determination unit 136.

[0053] The drive control signal generation unit 132 is a functional unit that generates the drive control signal Sd. Details of the drive control signal generation unit 132 will be described later.

[0054] The memory unit 137 is a functional unit for storing various data necessary for the drive control of the motor 20. For example, the memory unit 137 stores information 201 of a step-out determination threshold, which is a criterion for determining whether or not step-out occurs in the motor 20, and current reference value information 202, which will be described later, showing the relationship between the electrical angle θ and the current reference value Sis in the drive control of the motor 20. Part of the memory unit 137 is realized, for example, by utilizing the storage area of ​​a non-volatile memory device that retains data even when the power supply to the control unit 122 is stopped.

[0055] The step-out determination unit 136 is a functional unit that determines whether or not step-out has occurred in the motor 20 (step-out determination) based on the step-out determination threshold and the measured value Sbef of the back electromotive force measured by the back electromotive force measurement unit 126.

[0056] In this embodiment, the back electromotive force is measured, for example, as follows. For example, the drive control signal generation unit 132, described later, generates a drive control signal Sd to temporarily stop the application of voltage to coils 21a and 21b when the direction of the coil currents Ia and Ib flowing through the coils 21a and 21b of either phase A or phase B switches. The back electromotive force measurement unit 126 then individually (for each phase or each coil) measures the back electromotive force induced in the coils 21a and 21b of the phase from which the voltage application has been stopped during the period when the voltage application to the coils 21a and 21b has been stopped.

[0057] The step-out determination unit 136 compares the measured value Sbef of the back electromotive force measured by the back electromotive force measurement unit 126 with the step-out determination threshold stored in the memory unit 137. For example, the step-out determination unit 136 determines that step-out has occurred in the motor 20 if the measured value Sbef of the back electromotive force is lower than the step-out determination threshold, and determines that step-out has not occurred in the motor 20 if the measured value Sbef of the back electromotive force is equal to or greater than the step-out determination threshold.

[0058] The drive control signal generation unit 132 generates a drive control signal Sd according to the result of the step-out determination by the step-out determination unit 136. For example, if the drive control signal generation unit 132 determines that step-out has occurred in the motor 20, it uses the drive control signal Sd to instruct the motor drive unit 142 to stop driving the motor 20.

[0059] The drive command acquisition unit 131 acquires a drive command Sc input from, for example, a higher-level device (ECU). As described above, the drive command Sc includes information specifying, for example, the target rotational position (target rotational position) of the motor 20. The drive command acquisition unit 11 acquires and outputs information on the target rotational position of the motor 20 by, for example, analyzing the drive command Sc.

[0060] The drive control signal generation unit 132 generates a PWM signal so that the coil 21 of the motor 20 is in an excited state according to the specified excitation mode, and outputs it as a drive control signal Sd.

[0061] For example, the drive control signal generation unit 132 acquires information on the target rotation position output from the drive command acquisition unit 131. The drive control signal generation unit 132 generates a PWM signal for each phase according to the excitation mode specified by the excitation mode specification unit 135, so that the motor 20 moves to the target rotation position, and outputs it as a drive control signal Sd. Hereinafter, one period of the PWM signal, that is, the period in which the PWM signal is generated, will be referred to as the "PWM period".

[0062] The excitation mode designation unit 135 is a functional unit that designates the excitation mode and instructs the drive control signal generation unit 132 to generate the drive control signal Sd.

[0063] Now, let's explain the excitation mode. The excitation mode is information that indicates the excitation state of coil 21.

[0064] The motor drive control device 10 according to this embodiment has a charge mode and a damping mode as excitation modes.

[0065] First, let me explain the charge mode. The charge mode is an excitation mode that increases the current in coil 21.

[0066] Figure 5A is a diagram illustrating the charging mode. As shown in Figure 5A, the coils 21 of each phase of the motor 20 are connected to the inverter circuit 143 (H-bridge circuit) that constitutes the motor drive unit 142. As shown in Figure 5A, the inverter circuit 143 includes, for example, transistors Q1 to Q4 as switches and diodes D1 to D4.

[0067] Transistors Q1 and Q2 are connected in series between the power supply voltage VDD and ground potential via a shunt resistor acting as a current sensor 144. Similarly, transistors Q3 and Q4 are connected in series between the power supply voltage VDD and ground potential via a shunt resistor acting as a current sensor 144. The negative terminal (AN or BN) of coil 21 is connected to the node where transistors Q1 and Q2 are commonly connected, and the positive terminal (AP or BP) of coil 21 is connected to the node where transistors Q3 and Q4 are commonly connected.

[0068] 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 the ground potential GND, and the cathode of diode D2 is connected to the node where transistors Q1 and Q2 are commonly connected.

[0069] 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 the ground potential GND, and the cathode of diode D4 is connected to the node where transistors Q3 and Q4 are commonly connected.

[0070] Diodes D1 to D4 may be, for example, parasitic diodes of transistors Q1 to Q4, or they may be implemented by electronic components provided separately from transistors Q1 to Q4.

[0071] In charge mode, coil 21 is connected between the power supply voltage VDD and the ground potential GND, and is excited in either the positive or negative direction.

[0072] For example, as shown in Figure 5A, by turning off transistors Q1 and Q4 and turning on transistors Q2 and Q3, current flows from the positive terminal (AP / BP) side of coil 21 to the negative terminal (AN / BN) side of coil 21, and coil 21 is excited in the positive direction. On the other hand, by turning off transistors Q2 and Q3 and turning on transistors Q1 and Q4, current flows from the negative terminal (AN / BN) side of coil 21 to the positive terminal (AP / BP) side of coil 21, and coil 21 is excited in the negative direction.

[0073] Next, I will explain the attenuation modes. The damping mode is a mode that dampens the current in the coil 21. In this embodiment, the damping mode includes a low-speed damping mode that regenerates the current in the coil 21, and a high-speed damping mode that regenerates the current in the coil 21 at a faster rate than the low-speed damping mode.

[0074] Figure 5B is a diagram illustrating the low-speed damping mode. For example, when attenuating the current in coil 21 that was excited in the positive direction by the charge mode (see Figure 5A), the slow attenuation mode turns off transistors Q1 and Q3 in the inverter circuit 143 and turns on transistors Q2 and Q4. As a result, as shown in Figure 5B, the current in coil 21 can be regenerated to the ground potential GND side and attenuated. Similarly, when attenuating the current in coil 21 that was excited in the negative direction, the slow attenuation mode turns off transistors Q1 and Q3 and turns on transistors Q2 and Q4, thereby regenerating the current in coil 21 to the ground potential GND side and attenuating it.

[0075] Figure 5C is a diagram illustrating the fast decay mode. For example, when attenuating the current in coil 21 that was excited in the positive direction by the charge mode (see Figure 5A), the high-speed attenuation mode turns off transistors Q2 and Q3 in the inverter circuit 143 and turns on transistors Q1 and Q4. As a result, as shown in Figure 5C, the current in coil 21 can be regenerated to the power supply voltage VDD side. At this time, since coil 21 is excited in the opposite direction (negative) to the previous excitation direction (positive), the current in coil 21 can be attenuated faster than in the low-speed attenuation mode.

[0076] When attenuating the current in coil 21, which was excited in the negative direction, the high-speed attenuation mode turns off transistors Q1 and Q4 and turns on transistors Q2 and Q3 in the inverter circuit 143. This allows the current in coil 21 to be regenerated to the power supply voltage VDD side. At this time, since coil 21 is excited in the opposite direction (positive) to the previous excitation direction (negative), the current in coil 21 can be attenuated faster than in the low-speed attenuation mode.

[0077] The drive control signal generation unit 132 generates a drive control signal Sd based on the excitation mode specified by the excitation mode specification unit 135.

[0078] For example, if a charge mode is specified in which coil 21 is excited in the positive direction, the drive control signal generation unit 132 generates a drive control signal Sd that turns on transistors Q2 and Q3 and turns off transistors Q1 and Q4, as shown in Figure 5A.

[0079] On the other hand, if the low-speed decay mode is specified after the coil 21 is excited in the positive direction, the drive control signal generation unit 132 generates a drive control signal Sd that turns on transistors Q2 and Q4 and turns off transistors Q1 and Q3, as shown in Figure 5B. Also, if the high-speed decay mode is specified after the coil 21 is excited in the positive direction, the drive control signal generation unit 132 generates a drive control signal Sd that turns on transistors Q1 and Q4 and turns off transistors Q2 and Q3, as shown in Figure 5C.

[0080] When the coil 21 is excited in the negative direction, the drive control signal generation unit 132 generates a drive control signal Sd according to the specified excitation mode so that the current flows in the opposite direction to the case when the coil is excited in the negative direction as described above.

[0081] The current value acquisition unit 133 is a functional unit that acquires the measured values ​​of the current flowing through the coils 21a and 21b of the motor 20. The current value acquisition unit 133 acquires the measured value Sia of the current of the A-phase coil 21a, which is measured by the current measurement unit 124, and the measured value Sib of the current of the B-phase coil 21b, which is measured by the current measurement unit 124. For example, the current value acquisition unit 133 acquires the measured values ​​Sia and Sib of the current for each PWM period, as described later. Hereinafter, when the measured values ​​Sia and Sib of the current are not distinguished, they will be referred to as "measured value Si of the current".

[0082] The current reference value setting unit 134 is a functional unit that sets the current reference value Sis, which serves as the reference for the current of the coil 21.

[0083] The current reference value setting unit 134 sets a current reference value Sis, which serves as the reference for currents Ia and Ib, at each PWM cycle of the PWM signal (drive control signal Sd) so that the currents Ia and Ib flowing through the coil 21 change sinusoidally. For example, the current reference value setting unit 134 changes the current reference value Sis in a stepwise manner so that the current Ia of the A-phase coil 21a and the current Ib of the B-phase coil 21b are sinusoidal, and the phases of current Ia and current Ib are 90 degrees apart.

[0084] For example, the memory unit 137 stores current reference value information 202 that shows the correspondence between the electrical angle θ and the current reference value Sis. Here, the current reference value information 202 is information (for example, a function or table) that associates the current reference value Sis with each electrical angle θ such that the current reference value Sis is sinusoidal in the range of electrical angle θ = 0 to 360°.

[0085] The current reference value setting unit 134 reads out the current reference value Sis corresponding to the electrical angle θ at each PWM period from the current reference value information 202 and outputs it sequentially.

[0086] The excitation mode selection unit 135 compares the measured value of the coil 21 current acquired by the current value acquisition unit 133 with the current reference value Sis set by the current reference value setting unit 134, and determines the excitation mode based on the comparison result.

[0087] The excitation mode selection unit 135 compares the measured current Si of the coil 21, acquired by the current value acquisition unit 133, with the current reference value Sis for each PWM cycle. For example, at the start of one PWM cycle, the excitation mode is determined by comparing the measured current Si with the current reference value Sis.

[0088] If the measured current Si has not reached the current reference value Sis, the excitation mode designation unit 135 designates the charge mode as the excitation mode. On the other hand, if the measured current Si has reached the current reference value Sis, the excitation mode designation unit 135 designates the attenuation mode as the excitation mode.

[0089] The comparison of the measured current Si with the current reference value Sis and the determination of the excitation mode are performed for each phase. Specifically, the excitation mode designation unit 135 determines the excitation mode of the A-phase coil 21 by comparing the measured current Sia of the A-phase coil 21a with the current reference value Sis for each PWM period, and also determines the excitation mode of the B-phase coil 21b by comparing the measured current Sib of the B-phase coil 21b with the current reference value Sis. The drive control signal generation unit 132 outputs a drive control signal Sd that instructs the on / off pattern of transistors Q1 to Q4 corresponding to the excitation mode designated by the excitation mode designation unit 135.

[0090] Figure 6 is an example of a timing chart showing the temporal changes in the motor coil current and drive control signal. From the top to the bottom of the page in Figure 6, the waveforms of the current Ia and voltage of the A-phase coil 21a are shown.

[0091] In the motor drive control device 10 according to this embodiment, the current reference value setting unit 134 alternately repeats, for each coil 21a, 21b (for each phase) of the drive target, a current increase period TI in which the current reference value Sis increases in the positive or negative direction and a current decay period TD in which the current reference value Sis changes toward zero. Then, the excitation mode specifying unit 135 specifies an excitation mode so that the measured value Si of the current does not exceed the current reference value Sis, and the drive control signal generation unit 132 generates a drive control signal Sd corresponding to the specified excitation mode. Thereby, as shown in FIG. 6, the current of each phase coil 21 is controlled to be sinusoidal.

[0092] Note that, in FIG. 6, as an example, the phase of the current Ia of the coil 21a of the A phase is shown. When the motor 20 is a two-phase stepping motor having a coil of the A phase and a coil of the B phase, the phase of the current Ib of the coil 21b of the B phase (not shown) is detected with a 90-degree shift from the phase of the current Ia of the coil 21a of the A phase.

[0093] Specifically, the excitation mode specifying unit 135 compares the measured value Si of the current with the current reference value Sis for each PWM cycle in the current increase period TI and the current decay period TD, and switches the excitation mode.

[0094] For example, at the timing when one PWM cycle starts, the measured value Si of the current is compared with the current reference value Sis. If the measured value Si of the current has not reached the current reference value Sis (Si < Sis), the excitation mode specifying unit 135 specifies "charge mode" as the excitation mode. Then, when the measured value Si of the current reaches the current reference value Sis within that PWM cycle, the excitation mode specifying unit 135 switches the excitation mode from "charge mode" to "decay mode" and maintains the decay mode until the end of that PWM cycle.

[0095] Furthermore, if the measured current Si reaches the current reference value Sis (Si ≥ Sis) at the start of one PWM cycle, the excitation mode designation unit 135 designates "attenuation mode" as the excitation mode and maintains the attenuation mode until the end of that PWM cycle.

[0096] Thus, the excitation mode designation unit 135 switches the excitation mode at each PWM cycle, during both the current increase period TI and the current decay period TD, based on the comparison result between the measured current value Si and the current reference value Sis.

[0097] On the other hand, the excitation mode designation unit 135 differentiates the decay mode during the current increase period TI from the decay mode during the current decay period TD. Specifically, the excitation mode designation unit 135 selects the "slow decay mode" as the decay mode during the current increase period TI. That is, during the current increase period TI, either the charge mode or the slow decay mode is selected as the excitation mode. Furthermore, during the current decay period TD, the excitation mode designation unit 135 selects a mixed decay mode that alternately switches between the "slow decay mode" and the "fast decay mode" as the decay mode. The decay modes during the current decay period TD will be explained in detail below.

[0098] Figure 7 is an enlarged view of a portion of the current decay period TD in Figure 6.

[0099] As shown in Figure 7, the current decay period TD, during which the current in 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 initial predetermined period in the current decay period TD. The second decay period Td2 is the remaining predetermined period in the current decay period TD after the first decay period Td1 (Td2 = TD - Td1).

[0100] The lengths of the first decay period Td1 and the second decay period Td2 are preset. For example, the period during which the electrical angle θ ranges from 90° to 120° (270° to 300°) is set as the first decay period Td1, and the period during which the electrical angle θ ranges from 120° to 180° (300° to 360°) is set as the second decay period Td2.

[0101] As shown in FIG. 7, in the first decay period Td1, the excitation mode designating unit 135 selects the "low-speed decay mode" as the decay mode, and in the second decay period Td2, the excitation mode designating unit 135 selects the "mixed decay mode" in which the low-speed decay mode and the high-speed decay mode are alternately switched as the decay mode.

[0102] FIG. 8 is a diagram showing an example of the temporal change of the current in the coil 21 during the first decay period Td1.

[0103] In the figure, the horizontal axis represents time t, and the vertical axis represents current. The reference numeral 500 represents the temporal change of the current in the coil 21 (the measured value Si of the current in the coil 21). Also, FIG. 8 shows the case where the current reference value Sis is set to "Ith2" in the first PWM period from time 0 to time t2, and the current reference value Sis is set to "Ith1 (<Ith2)" in the PWM periods after time t2.

[0104] As shown in FIG. 8, at the time t0 when one PWM period starts, the excitation mode designating unit 135 compares the measured value Si of the current with the current reference value Sis (= Ith2). At this time, since the measured value Si of the current in the coil 21 has not reached the current reference value Sis (= Ith2), the excitation mode designating unit 135 sets the excitation mode to the "charge mode" (see FIG. 5A). Thereby, the current in the coil 21 increases.

[0105] Thereafter, when the measured value Si of the current reaches the current reference value Sis (= Ith2) at time t1, the excitation mode designating unit 135 switches the excitation mode from the "charge mode" to the "low-speed decay mode (decay mode)", and maintains the "low-speed decay mode" until the time t2 when the next PWM period starts.

[0106] Then, at time t2 when a new PWM period starts, the excitation mode specifying unit 135 compares the measured value Si of the current with the current reference value Sis (= Ith2). As shown in FIG. 8, at time t2, since the measured value Si of the current is higher than the current reference value Sis (= Ith2), the excitation mode specifying unit 135 continues to set the excitation mode to the low-speed decay mode and maintains the low-speed decay mode until time t3 when the next PWM period starts.

[0107] Thus, in the first decay period Td1 during the current decay period TD, the low-speed decay mode is selected as the decay mode.

[0108] FIG. 9 is a diagram showing an example of the temporal change of the current in the coil 21 during the second decay period Td2.

[0109] In FIG. 9, the horizontal axis represents time t, and the vertical axis represents the current. The reference numeral 501 represents the temporal change of the current in the coil 21 (the measured value Si of the current in the coil 21). Also shown in FIG. 9 is the case where the current reference value Sis is set to “Ith2” in the first PWM period from time 0 to time t2, and the current reference value Sis is set to “Ith1 (< Ith2)” in the PWM periods after time t2.

[0110] As shown in FIG. 9, during the remaining second decay period Td2 of the current decay period TD, the excitation mode specifying unit 135 designates the low-speed decay mode as the decay mode in the first period T1 which is the first period within the PWM period for each PWM period, and designates the high-speed decay mode as the decay mode in the second period T2 which is the remaining period after the first period T1 within the PWM period.

[0111] Specifically, in the first period T1, when the measured value Si of the current in the coil 21 has not reached the current reference value Sis, the excitation mode specifying unit 135 designates the “charge mode” as the excitation mode, and when the measured value Si of the current has reached the current reference value Sis, the excitation mode specifying unit 135 designates the “low-speed decay mode” as the excitation mode.

[0112] Furthermore, the excitation mode designation unit 135 designates the high-speed decay mode as the excitation mode during the second period T2.

[0113] For example, as shown in Figure 9, at time t0 when the PWM period starts, the excitation mode designation unit 135 compares the measured current Si with the current reference value Sis (=Ith2). At this time, since the measured current Si of the coil 21 has not reached the current reference value Sis (=Ith2), the excitation mode designation unit 135 sets the excitation mode to "charge mode" (see Figure 5A). As a result, the current of the coil 21 increases.

[0114] As shown in Figure 9, when the measured current Si reaches the current reference value Sis (=Ith2) at time t1, the excitation mode designation unit 135 switches the excitation mode from "charge mode" to "slow decay mode (decay mode)" (see Figure 5B). As a result, as shown in Figure 9, the current in the coil 21 decreases at a constant rate.

[0115] Subsequently, at time tc1, the excitation mode designation unit 135 switches the attenuation mode from "slow attenuation mode" to "high-speed attenuation mode" and maintains the high-speed attenuation mode until time t2 when the next PWM cycle begins (see Figure 5C). As a result, the current in coil 21 decreases at a steeper rate than in the slow attenuation mode.

[0116] Then, at time t2 when a new PWM cycle begins, the current reference value Sis is updated from Ith2 to Ith1, and the excitation mode designation unit 135 compares the measured current Si with the current reference value Sis (=Ith1). At this time, as shown in Figure 9, since the measured current Si is lower than the current reference value Sis (=Ith1), the excitation mode designation unit 135 sets the excitation mode to "charge mode". As a result, the current in coil 21 increases.

[0117] When the measured current Si reaches the current reference value Sis (=Ith1) at time t3, the excitation mode designation unit 135 switches the excitation mode from "charge mode" to "slow decay mode". As a result, the current in coil 21 decreases at a constant rate, as shown in Figure 9.

[0118] Subsequently, at time tc2, the excitation mode designation unit 135 switches the attenuation mode from "slow attenuation mode" to "high-speed attenuation mode" and maintains the "high-speed attenuation mode" until time t4 when the next PWM cycle begins. As a result, the current in coil 21 decreases at a steeper rate than in the slow attenuation mode.

[0119] Thus, in the first period T1 of the PWM cycle, the "slow decay mode" is selected as the decay mode, and in the remaining second period T2 of the PWM cycle, the "fast decay mode" is selected as the decay mode. As a result, in the second decay period Td2 of the current decay period TD, the decay mode alternates between the "slow decay mode" and the "fast decay mode".

[0120] Here, the lengths of the first period T1 and the second period T2 within the PWM period (times tc1 and tc2 in Figure 9), that is, the ratio of the slow-attenuation mode to the fast-attenuation mode for one PWM period, may be fixed.

[0121] For example, by making the first period T1 (slow decay mode) longer than the second period T2 (fast decay mode) in the PWM cycle, the current can be gradually reduced within a single PWM cycle. Conversely, by making the second period T2 (fast decay mode) longer than the first period T1 (slow decay mode) in the PWM cycle, the current can be rapidly reduced within a single PWM cycle.

[0122] Furthermore, the lengths of the first period T1 and the second period T2 within the PWM cycle may be dynamically changed. For example, the excitation mode designation unit 135 may increase the ratio of the second period T2 (high-speed decay mode) to the PWM cycle in the second decay period Td2 in accordance with the decrease in the current reference value Sis. That is, the excitation mode designation unit 135 may shorten the first period T1 (low-speed decay mode) and lengthen the second period T2 (high-speed decay mode) as the current reference value Sis approaches zero. This makes it possible to rapidly reduce the current of the coil 21 as the current of the coil 21 approaches zero.

[0123] Next, the flow of the excitation mode switching control by the motor drive control device 10 according to the embodiment will be explained.

[0124] Figure 10 is a flowchart showing the flow of excitation mode switching control by the motor drive control device 10 according to the embodiment.

[0125] For example, when a drive command Sc is input to the motor drive control device 10 from a higher-level device, the control unit 122 starts PWM control to rotate the motor 20 (output shaft) to the target rotation position specified by the drive command Sc.

[0126] First, the control unit 122 starts one PWM cycle in the PWM control (step S1). Next, the current reference value setting unit 134 of the control unit 122 sets the current reference value Sis corresponding to the electrical angle θ at that time, based on the current reference value information 202 using the method described above (step S2).

[0127] Next, the excitation mode designation unit 135 of the control unit 122 determines whether the current time is the current increase period TI (step S3). If the current time is the current increase period TI (step S3: YES), the excitation mode designation unit 135 switches the excitation mode between the charge mode and the slow decay mode using the method described above, based on the comparison result between the measured value Si of the coil 21 obtained by the current value acquisition unit 133 and the current reference value Sis set in step S2 (step S4).

[0128] After step S4, the excitation mode designation unit 135 determines whether one PWM cycle has ended (step S5). If the PWM cycle has not ended (step S5: NO), the excitation mode designation unit 135 returns to step S4. On the other hand, if the PWM cycle has ended (step S5: YES), the drive control signal generation unit 132 of the control circuit 12 determines whether the motor 20 has reached the target rotation position (step S10).

[0129] If the motor 20 has not reached the target rotation position (step S10: NO), the control circuit 12 returns to step S1 and starts control for the next PWM cycle. On the other hand, if the motor 20 has reached the target rotation position (step S10: YES), the control circuit 12 stops the series of PWM control.

[0130] In step S3, if the current time is not the current increase period TI (step S3: NO), that is, if the current time is the current decay period TD, the excitation mode designation unit 135 determines whether the current time is the first decay period Td1 or not (step S6).

[0131] If the current time is the first decay period Td1 (step S6: YES), the excitation mode designation unit 135 switches the excitation mode between the charge mode and the slow decay mode based on the comparison result between the measured value Si of the coil 21 obtained by the current value acquisition unit 133 using the method described above and the current reference value Sis set in step S2 (step S7).

[0132] After step S7, the excitation mode designation unit 135 determines whether one PWM cycle has ended (step S9). If the PWM cycle has not ended (step S9: NO), the excitation mode designation unit 135 returns to step S6. On the other hand, if the PWM cycle has ended (step S9: YES), the drive control signal generation unit 132 of the control circuit 12 determines whether the motor 20 has reached the target rotation position (step S10). If the motor 20 has not reached the target rotation position (step S10: NO), the control circuit 12 returns to step S1 and starts control for the next PWM cycle. On the other hand, if the motor 20 has reached the target rotation position (step S10: YES), the control circuit 12 stops the series of PWM control.

[0133] In step S6, if the current time is not the first decay period Td1 (step S6:NO), that is, if the current time is the second decay period Td2, the excitation mode designation unit 135 switches the excitation mode between the charge mode and the mixed decay mode (low-speed decay mode, high-speed decay mode) based on the comparison result between the measured value Si of the coil 21 obtained by the current value acquisition unit 133 using the method described above and the current reference value Sis set in step S2 (step S8).

[0134] After step S8, the excitation mode designation unit 135 determines whether one PWM cycle has ended (step S9). If the PWM cycle has not ended (step S9: NO), the excitation mode designation unit 135 returns to step S6. On the other hand, if the PWM cycle has ended (step S9: YES), the drive control signal generation unit 132 of the control circuit 12 determines whether the motor 20 has reached the target rotation position (step S10). If the motor 20 has not reached the target rotation position (step S10: NO), the control circuit 12 returns to step S1 and starts control for the next PWM cycle. On the other hand, if the motor 20 has reached the target rotation position (step S10: YES), the control circuit 12 stops the series of PWM control.

[0135] Figure 11 shows the measured current of coil 21 when the motor is driven by a conventional motor drive control device as a comparative example.

[0136] Figure 12 shows the measured current of the coil 21 when the motor 20 is driven by the motor drive control device 10 according to the embodiment.

[0137] Figures 11 and 12 show the waveforms of the current Ia and voltage across the A-phase coil 21a, viewed from top to bottom of the page.

[0138] Conventional motor drive control devices, as shown in Figure 11, initially select a low-speed decay mode as the decay mode during the current decay period, and then select a high-speed decay mode after a certain period of time has elapsed to drive the motor. As a result, as shown by reference numeral 300 in Figure 11, the current changes significantly at the timing when the decay mode switches from the low-speed decay mode to the high-speed decay mode, causing significant distortion in the current waveform. This significant distortion in the current waveform may cause abnormal noise to be generated when the motor is driven.

[0139] On the other hand, as shown in Figure 12, the motor drive control device 10 according to this embodiment selects a mixed damping mode as the damping mode for the current damping period, initially selecting a low-speed damping mode, and then switching between the low-speed damping mode and the high-speed damping mode after a certain period of time has elapsed, in order to drive the motor.

[0140] As a result, as shown by reference numeral 301 in Figure 13, the change in current at the timing when the damping mode switches from the low-speed damping mode to the mixed damping mode is smaller compared to conventional motor drive control devices, and the distortion of the current waveform is reduced. This makes it possible to suppress the generation of abnormal noise when the motor is driven.

[0141] In the motor drive control device 10 according to this embodiment, the control unit 122 sets a current reference value Sis for each PWM period of the PWM signal (drive control signal Sd) so that the current flowing through the coil 21 changes sinusoidally. For each PWM period, the control unit 122 compares the measured value Si(Sia,Sib) of the current of the coil 21 acquired by the current value acquisition unit 133 with the current reference value Sis. If the measured value Si of the current has not reached the current reference value Sis, the control unit 122 specifies the charge mode as the excitation mode, and if the measured value Si of the current has reached the current reference value Sis, the control unit 122 specifies the attenuation mode as the attenuation mode in the first attenuation period Td1, which is the first period in the current attenuation period TD in which the current reference value changes toward zero (see Figure 8). In the second attenuation period Td2, which is the remaining period after the first attenuation period Td1 in the current attenuation period TD, the control unit 122 specifies a mixed attenuation mode that alternately switches between the low-speed attenuation mode and the high-speed attenuation mode as the attenuation mode (see Figure 9). The control unit 122 generates a drive control signal Sd corresponding to the excitation mode specified by the method described above, and controls the drive of the motor 20.

[0142] According to this, in the first decay period Td1 of the current decay period TD, the coil current is gradually decayed by the low-speed decay mode, and then in the second decay period Td2, the current is not rapidly decayed by the high-speed decay mode. Instead, a mixed decay mode, which alternately switches between the low-speed decay mode and the high-speed decay mode, can alternately generate a gradual decay and a rapid decay of the coil current. As a result, as described above, the change in current caused by the switching of the decay mode during the current decay period TD can be reduced, thereby reducing the distortion of the current in the sinusoidal coil and suppressing the generation of abnormal noise when the motor is driven.

[0143] Furthermore, in the motor drive control device 10 according to this embodiment, the control unit 122 specifies a low-speed decay mode as the decay mode for each PWM period in the second decay period Td2, in the first period T1 which is the first period within the PWM period, and specifies a high-speed decay mode as the decay mode for the second period T2 which is the remaining period after the first period T1 within the PWM period.

[0144] Specifically, as shown in Figure 9, the control unit 122, during the first period T1 of the PWM cycle within the second decay period Td2, specifies the charge mode as the excitation mode if the measured current Si has not reached the current reference value Sis, and specifies the slow decay mode as the excitation mode if the measured current Si has reached the current reference value Sis. Furthermore, the control unit 122 specifies the fast decay mode as the excitation mode during the second period T2 of the PWM cycle within the second decay period Td2.

[0145] According to this, a switch between a slow decay mode and a fast decay mode occurs within a single PWM cycle, making it possible to make the current change more gradual.

[0146] Furthermore, in the motor drive control device 10 according to this embodiment, the control unit 122 may increase the ratio of the second period T2 (high-speed decay mode) to the PWM period in the second decay period Td2 in accordance with the decrease in the current reference value Sis.

[0147] According to this, as described above, the closer the current in coil 21 approaches zero, the faster the current in coil 21 can be reduced, making it possible to bring the current waveform closer to a sine wave while suppressing distortion of the current waveform.

[0148] <<Extension of the Embodiment>> Although the present inventors have described the invention in detail based on embodiments, it goes without saying that the present invention is not limited thereto and can be modified in various ways without departing from its essence.

[0149] For example, in the above embodiment, in the second period T2 within the PWM period in the second decay period Td2, an example was shown where the excitation mode designating unit 135 sets the excitation mode to the "high-speed decay mode" without comparing the measured current value Si with the current reference value Sis (see FIG. 9), but the present invention is not limited to this. For example, the excitation mode designating unit 135 may also switch the excitation mode to the charge mode or the high-speed decay mode according to the comparison result between the measured current value Si and the current reference value Sis in the second period T2. This will be described in detail below.

[0150] FIG. 13 is a diagram showing another example of the temporal change of the current in the coil 21 in the second decay period Td2.

[0151] In the figure, the horizontal axis represents time t, and the vertical axis represents current. The reference numeral 502 represents the temporal change of the current (measured current value Si) in the coil 21. Also, in FIG. 13, a case is shown where the current reference value Sis is set to "Ith2" in the first PWM period from time 0 to time t2, and the current reference value Sis is set to "Ith1 (<Ith2)" in the PWM periods after time t2.

[0152] As shown in FIG. 13, when the measured current value Si of the current in the coil 21 has not reached the current reference value Sis in the first period T1, the excitation mode designating unit 135 designates the charge mode as the excitation mode, and when the measured current value Si of the current has reached the current reference value Sis, the excitation mode designating unit 135 designates the low-speed decay mode as the excitation mode.

[0153] Also, as shown in FIG. 13, when the measured current value Si of the current has not reached the current reference value Sis in the second period T2, the excitation mode designating unit 135 designates the charge mode as the excitation mode, and when the measured current value Si of the current has reached the current reference value Sis, the excitation mode designating unit (135) designates the high-speed decay mode as the excitation mode.

[0154] Thus, even during the second period T2 of each PWM cycle, by switching the excitation mode to "charge mode" or "high-speed decay mode" according to the comparison result between the measured current value Si and the current reference value Sis, it is possible to control the coil current more closely to the current reference value Sis. This makes it possible to reduce the distortion of the current waveform of the coil 21 and bring the current waveform closer to a sine wave.

[0155] Furthermore, the number of phases of the motor 20 in the above embodiment is not limited to two phases.

[0156] Furthermore, 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.

[0157] Furthermore, the flowchart described above is merely an example illustrating the operation and is not limited to it. In other words, the steps shown in each diagram of the flowchart are specific examples and are not limited to this flow. For example, the order of some processes may be changed, other processes may be inserted between each process, or some processes may be performed in parallel. [Explanation of Symbols]

[0158] 1...Actuator, 10...Motor drive control device, 12...Control circuit, 14...Drive circuit, 20...Motor (stepping motor), 21, 21a, 21b...Coil, 22...Rotor, 22n...N pole, 22s...S 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, 122...Control unit, 124...Current measurement unit, 126...Back electromotive force measurement unit, 131...Drive command acquisition unit, 132...Drive control signal generation unit, 133...Current value acquisition unit, 134...Current reference value setting unit, 1 35...Excitation mode selection unit, 136...Step loss determination unit, 137...Memory unit, 142...Motor drive unit, 143,143a,143b...Inverter circuit (H-bridge circuit), 144...Current sensor, 201...Step loss determination threshold information, 202...Current reference value information, AP,BP...Positive terminals of coil 21, AN,BN...Negative terminals of coil 21, Q1~Q4...Transistors, D1~D4...Diodes, Ia,Ib...Current of coil 21, Sbef...Measured value of back electromotive force, Si,Sia,Sib...Measured value of coil current, Sis...Current reference value, TI...Current increase period, TD...Current decay period, Td1...First decay period, Td2...Second decay period, T1...First period, T2...Second period.

Claims

1. A control circuit that generates a drive control signal to control the drive of a motor, The system includes a drive circuit that energizes the motor coils based on the drive control signal, The aforementioned control circuit is A current value acquisition unit that acquires a measured value of the current of the coil, A drive control signal generation unit generates a PWM signal so that the coil is in a state corresponding to the specified excitation mode and outputs it as the drive control signal, A current reference value setting unit sets a current reference value that serves as a reference for the current at each PWM period of the PWM signal, so that the current flowing through the coil changes sinusoidally. The system includes an excitation mode designation unit that, at each PWM cycle, compares the measured value of the current measured by the current value acquisition unit with the current reference value, and, if the measured value of the current has not reached the current reference value, designates a charge mode that increases the current as the excitation mode, and if the measured value of the current has reached the current reference value, designates an attenuation mode that decreases the current as the excitation mode. The excitation mode designation unit designates a low-speed decay mode that regenerates the current as the decay mode during the first decay period, which is the first period in the current decay period during which the current reference value changes toward zero. The excitation mode designation unit designates a mixed decay mode as the decay mode in the second decay period, which is the remaining period after the first decay period in the current decay period, which alternately switches between the low-speed decay mode and a high-speed decay mode that regenerates the current at a higher speed than the low-speed decay mode. The excitation mode designation unit, for each PWM cycle in the second decay period, designates the low-speed decay mode as the decay mode in the first period, which is the first period within the PWM cycle, and designates the high-speed decay mode as the decay mode in the second period, which is the remaining period after the first period within the PWM cycle. The excitation mode designation unit increases the ratio of the second period to the PWM period during the second decay period in accordance with the decrease in the current reference value. Motor drive control device.

2. In the motor drive control device according to claim 1, The excitation mode designation unit, during the first period, designates the charge mode as the excitation mode if the measured value of the current has not reached the current reference value, and designates the low-speed decay mode as the excitation mode if the measured value of the current has reached the current reference value. The excitation mode designation unit designates the high-speed decay mode as the excitation mode during the second period. Motor drive control device.

3. In the motor drive control device according to claim 1, The excitation mode designation unit, during the first period, designates the charge mode as the excitation mode if the measured value of the current has not reached the current reference value, and designates the low-speed decay mode as the excitation mode if the measured value of the current has reached the current reference value. The excitation mode designation unit, during the second period, designates the charge mode as the excitation mode if the measured value of the current has not reached the current reference value, and designates the high-speed decay mode as the excitation mode if the measured value of the current has reached the current reference value. Motor drive control device.

4. The motor and, A motor drive control device as described in any one of claims 1 to 3, An actuator comprising a power transmission mechanism for transmitting the rotational force of the motor to a drive object.

5. A motor drive control method for controlling the drive of a motor using a motor drive control device, The motor drive control device generates a PWM signal so that the motor coils are in an excited state corresponding to a specified excitation mode, and drives the motor based on the PWM signal (first step), The motor drive control device performs a second step of setting a current reference value that serves as a reference for the current at each PWM period of the PWM signal, such that the current flowing through the coil is sinusoidal. The motor drive control device compares the measured current value with the current reference value set in the second step for each PWM cycle, and if the measured current value has not reached the current reference value, it specifies a charge mode to increase the current as the excitation mode, and if the measured current value has reached the current reference value, it sets the excitation mode as: The third step includes specifying a decay mode that reduces the current, The previous third step is, The motor drive control device, in the first decay period which is the first period in the current decay period during which the current reference value changes toward zero, specifies a low-speed decay mode that regenerates the current as the decay mode, in a fourth step, The motor drive control device includes a fifth step of specifying, in the second decay period which is the period after the first decay period in the current decay period, a mixed decay mode which alternately switches between the low-speed decay mode and a high-speed decay mode which regenerates the current at a higher speed than the low-speed decay mode, as the decay mode. The fifth step is that the motor drive control device, for each PWM cycle in the second damping period, specifies the low-speed damping mode as the damping mode in the first period, which is the first period within the PWM cycle, and specifies the high-speed damping mode as the damping mode in the second period, which is the remaining period after the first period within the PWM cycle. The step includes increasing the ratio of the second period to the PWM period in the second decay period in accordance with the decrease in the current reference value. Motor drive control method.

Images