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

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

Technical Field

[0006] ,

[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 controlling the drive of motors such as stepping motors and brushless DC motors, a method of driving a coil so that a coil current, which is a current flowing through the coil of the motor, becomes sinusoidal 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 stepwise manner so that the coil current of each phase constituting the stepping motor becomes sinusoidal, monitors the coil current, and switches the excitation state of the coil of each phase so that the detected value of the coil current does not exceed the reference value.

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

[0005] Generally, when controlling the drive 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 coil current 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 current changes significantly. This change in the amount of damping in the coil current causes significant distortion (ripple) in the waveform of the coil current, and this distortion may cause loud abnormal noises to be generated from the stepping motor.

[0009] On the other hand, if the duration of the slow decay mode is made longer than the fast decay mode during the decay period in order to reduce the ripple of the coil current, it may not be possible to sufficiently reduce the coil current, and it may not be possible to change the coil current in a sinusoidal manner.

[0010] This invention has been made in view of the above-mentioned problems, and aims to appropriately control the coil current of a motor. [Means for solving the problem]

[0011] 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 coil current, which is the 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 it as the drive control signal, a current reference value setting unit that sets a current reference value for the coil current at each PWM period of the PWM signal so that the current flowing through the coil changes sinusoidally, and, at each PWM period, if the measured value of the coil current measured by the current value acquisition unit is lower than the current reference value, a charge mode that increases the coil current is designated as the excitation mode, and if the measured value of the coil current is equal to or greater than the current reference value, an attenuation mode that decreases the coil current is designated as the excitation mode. The excitation mode specification unit has a magnetic mode specification unit, and the damping mode includes a low-speed damping mode for regenerating the coil current, a high-speed damping mode for regenerating the coil current at a higher speed than the low-speed damping mode, and a mixed damping mode for regenerating the coil current by combining the low-speed damping mode and the high-speed damping mode, wherein when the coil current is damped by the mixed damping mode, the excitation mode specification unit first specifies one of the low-speed damping mode and the high-speed damping mode, then specifies the other of the low-speed damping mode and the high-speed damping mode, and when the excitation mode specification unit detects that the coil current has reached the current reference value in the mixed damping mode, it performs an increase process to make the proportion of the high-speed damping mode period in the damping period within the PWM period greater than the proportion of the high-speed damping mode period in the damping period within the previous PWM period. [Effects of the Invention]

[0012] According to the motor drive control device of the present invention, it is possible to appropriately control the coil current of the motor. [Brief explanation of the drawing]

[0013] [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 diagram schematically shows the configuration of a motor and a motor drive control device. [Figure 3] This is a block diagram showing the configuration of a motor drive control device according to an embodiment. [Figure 4A] This is a diagram to explain the charge mode. [Figure 4B] This is a diagram illustrating the low-speed damping mode. [Figure 4C] This is a diagram illustrating the high-speed damping mode. [Figure 5] This is a timing chart showing the time-dependent changes in the motor's coil current and drive control signal. [Figure 6] Figure 5 shows an enlarged view of a portion of the current decay period TD. [Figure 7] This figure shows an example of the temporal change in coil current during the first decay period Td1. [Figure 8] This figure shows an example of the temporal change in coil current during the second decay period Td2. [Figure 9] This flowchart shows an example of an incrementing process that increases the duration of the fast decay mode in a mixed decay mode. [Figure 10A] This figure shows the measured coil current when a motor is driven by a motor drive control device according to a prior art study by the present inventor, which serves as a comparative example. [Figure 10B] This figure shows the measured coil current when the motor is driven by the motor drive control device according to the embodiment. [Modes for carrying out the invention]

[0014] 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 will be omitted.

[0015] 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 an embodiment.

[0016] 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 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.

[0017] 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.

[0018] As shown in FIG. 1, the actuator 1 is covered with a case 51 and a cover 52. Inside the actuator 1, there are housed a motor 20, a motor drive control device 10 for controlling the drive of the motor 20, and a primary gear 26, a secondary gear 31, a tertiary gear 32, and an output gear 33 as a power transmission mechanism for transmitting the rotational force of the motor 20 to the drive target.

[0019] 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 coil of phase A and a coil of phase B. 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.

[0020] Figure 2 is a schematic diagram showing the configuration of the motor 20 and the motor drive control device 10.

[0021] 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 (not shown).

[0022] Coils 21a and 21b are coils that excite the stator (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 143a and 143b that constitute the drive circuit 14. Details of inverter circuits 143a and 143b will be described later.

[0023] 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.

[0024] In the following explanation, when coil 21a and coil 21b are not distinguished, they will simply be referred to as "coil 21".

[0025] 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.

[0026] The stator (not shown) 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.

[0027] As shown in Figure 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 the drive target.

[0028] 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.

[0029] 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.

[0030] 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.

[0031] As shown in Figure 2, the motor drive control device 10 includes a control circuit 12 and a drive circuit 14.

[0032] The control circuit 12 generates a PWM signal as a drive control signal to control the drive of the motor 20 so that the coil current, which is the current flowing through the coil 21 of the motor 20, matches the current reference value, which is the target value of the coil current. Specifically, based on the drive command Sc from the higher-level device (ECU), 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, and supplies them 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, the drive control signal Sda and the drive control signal Sdb will be referred to as "drive control signal Sd".

[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 an inverter circuit 143 for driving the motor 20's coil 21 and a current sensor 144 for detecting the current flowing through the motor 20's coil 21.

[0035] The inverter circuit 143 supplies drive power to the motor 20 based on the drive control signal Sd. As shown in Figure 2, the inverter circuit 143 is provided in correspondence to each of the coils 21a and 21b to be driven. For example, as shown in Figure 2, an inverter circuit 143a is provided for driving the A-phase coil 21a and an inverter circuit 143b is provided for driving the B-phase coil 21b. The inverter circuits 143a and 143b are configured, for example, by H-bridge circuits.

[0036] In the following explanation, when inverter circuits 143a and 143b are not distinguished, both inverter circuits 143a and 143b may 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 current Ia to flow through coil 21a by applying a voltage Va between the positive terminal AP and the negative terminal AN based on the drive control signal Sda output from control circuit 12. Inverter circuit 143b causes current Ib to flow through coil 21b by applying a voltage Vb between the positive terminal BP and the negative terminal BN based on the drive control signal Sdb output from control circuit 12.

[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 coil 21a, the voltage Va at the positive terminal AP with respect 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 coil 21a, the voltage Va at the positive terminal AP with respect to the negative terminal AN is set to "negative". The same applies when exciting the B-phase coil 21b. In the following explanation, the current flowing through coil 21a may be referred to as "coil current Ia", and the current flowing through coil 21b may be referred to as "coil current Ib".

[0040] The specific circuit configuration of the inverter circuit 143 and the specific method of exciting the coil 21 using the inverter circuit 143 will be described later.

[0041] As shown in Figure 2, the current sensors 144 are provided, for example, corresponding to each of the coils 21a and 21b that are to be driven. For example, as shown in Figure 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.

[0042] Current sensors 144a and 144b each include a shunt resistor that converts the coil currents Ia and Ib of the coils 21a and 21b to be detected into voltages. As will be described in detail later, a shunt resistor is provided for each phase coil 21a and 21b and is connected in series with the inverter circuits 143a and 143b to the ground potential GND side or the power supply voltage VDD. Current sensor 144a outputs the voltage across the shunt resistor as a current detection signal Via representing the measured value of the A-phase coil current Ia. Current sensor 144b outputs the voltage across the shunt resistor as a current detection signal Vib representing the measured value of the B-phase coil current Ib.

[0043] The control circuit 12 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 circuit 12 has a rewritable non-volatile memory, such as flash memory or EEPROM (Electrically Erasable Programmable Read-Only Memory), as its memory.

[0044] The control circuit 12 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 circuit 12 generates drive control signals Sda and Sdb to drive the inverter circuits 143a and 143b so as to excite the A-phase coil 21a and the B-phase coil 21b at predetermined timings based on a predetermined excitation method, thereby moving (rotating) the motor 20 to the target rotation position specified by the drive command Sc.

[0045] 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.

[0046] The control circuit 12 generates a drive control signal Sd using a two-phase microstepping method. For example, the control circuit 12 changes the current reference values ​​(target current values) Sisa and Sisb, which are target values ​​for 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 are sinusoidal. It also 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 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 according to the 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.

[0047] 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.

[0048] As shown in Figure 3, the control circuit 12 includes, for example, a current value acquisition unit 120, a comparison unit 121, a current reference value setting unit 122, a storage unit 123, an excitation mode specification unit 124, and a drive control signal generation unit 126 as functional blocks for realizing the functions described above. These functional blocks are realized by the processor within the MCU, as described above, performing 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.

[0049] 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 step based on the back electromotive force of the motor 20.

[0050] The drive control signal generation unit 126 is a functional unit that generates PWM signals as drive control signals Sda and Sdb. Hereinafter, one cycle of the PWM signal, that is, the period in which one PWM signal is generated, will be referred to as the "PWM period". Details of the drive control signal generation unit 126 will be described later.

[0051] The current value acquisition unit 120 is a functional unit that acquires 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.

[0052] 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). Based on the magnitude (voltage) of the input current detection signals Via and Vib, the current value acquisition unit 120 calculates the measured values ​​Sia and Sib of the coil currents Ia and Ib of each phase.

[0053] 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 measured 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 measured value Sib of the B-phase coil current Ib. For example, the current value acquisition unit 120 outputs the measured value Sia of the A-phase coil current Ia and the measured value Sib of the B-phase coil current Ib, respectively, for each PWM period. Hereafter, when the measured value Sia of the coil current Ia and the measured value Sib of the coil current Ib are not distinguished, the measured value Sia of the coil current Ia and the measured value Sib of the coil current Ib will be referred to as "measured value Si of coil current".

[0054] The current reference value setting unit 122 is a functional unit that sets current reference values ​​Sisa and Sisb, which serve as the reference 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 sinusoidally. For example, in response to instructions from the drive command acquisition unit 131, which will be described later, the current reference value setting unit 122 changes the current reference values ​​Sisa and Sisb in a stepwise manner 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, the current reference value Sisa and the current reference value Sisb will be referred to as "current reference value Sis".

[0055] For example, the memory unit 123 stores current reference value information that shows the correspondence between the electrical angle θ and the current reference value Sis. Here, the current reference value information 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°.

[0056] The current reference value setting unit 122 reads out current reference values ​​Sisa and Sisb corresponding to the electrical angle θ at each PWM period from the current reference value information stored in the storage unit 123 and outputs them sequentially.

[0057] The memory unit 123 is a functional unit for storing various data necessary for driving control of the motor 20. At least a portion of the memory unit 123 is implemented, for example, by utilizing the storage area of ​​a non-volatile memory device that retains data even when the power supply to the control circuit 12 is stopped.

[0058] In addition to the current reference value information mentioned above, the memory unit 123 stores, for example, the minimum time Tmin, the unit increase time ΔT, the specified times Tf1 and Tf2, and the upper limit time Tlmt. Details of this information will be described later.

[0059] 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 cycle. 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 timing when one PWM cycle of phase A starts, and outputs a comparison result Scma. Also, at the timing when one PWM cycle of phase B starts, the comparison unit 121 starts comparing the measured value Sib of the coil current Ib with the current reference value Sisb, and outputs a comparison result Scmb.

[0060] When the comparison results Scma and Scmb are not distinguished from each other, the comparison results Scma and Scmb are denoted as "comparison result Scm".

[0061] [[ID=I]] For example, when one PWM cycle starts, the comparison unit 121 starts the 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 the 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 becomes equal to or greater than the current reference value Sis (Si ≥ Sis), the comparison unit 121 outputs a signal of the second logic level (e.g., low level), which is the opposite of 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 that PWM cycle ends. Then, when one PWM cycle ends and the next PWM cycle starts, the comparison unit 121 starts the comparison process of the measured value Si of the coil current and the current reference value Sis again.

[0062] 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 cycle of each phase. Thereby, by referring to the comparison result Scmb by the comparison unit 121, it is possible to determine whether the coil current of the motor 20 has reached the current reference value.

[0063] The drive control signal generation unit 126 includes a drive command acquisition unit 127 and a PWM signal generation unit 128.

[0064] The drive command acquisition unit 127 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 rotation position (target rotation position) of the motor 20. By analyzing the drive command Sc, the drive command acquisition unit 127 acquires and outputs the information of the target rotation position of the motor 20, and also instructs other functional units (for example, the current reference value setting unit 122, the excitation mode specification unit 124, and the PWM signal generation unit 128, etc.) to start the process for driving the motor 20.

[0065] The PWM signal generation unit 128 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 drive control signals Sda and Sdb.

[0066] For example, the PWM signal generation unit 128 acquires information on the target rotation position output from the drive command acquisition unit 127. The PWM signal generation unit 128 generates a PWM signal for each phase according to the excitation mode specified by the excitation mode specification unit 124, so that the motor 20 moves to the target rotation position, and outputs it as drive control signals Sda and Sdb.

[0067] The excitation mode designation unit 124 is a functional unit that designates the excitation mode and instructs the drive control signal generation unit 126 to generate the 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 from the comparison unit 121.

[0068] Now, let's explain the excitation modes. The excitation mode is an operating mode that specifies the excitation state of the coil 21. The motor drive control device 10 according to this embodiment has a charge mode and a damping mode as excitation modes.

[0069] First, let me explain the charge mode. The charge mode is an operating mode that increases the coil current.

[0070] Figure 4A is a diagram illustrating the charging mode.

[0071] 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. Therefore, the excitation mode will be explained using the inverter circuit 143a for driving the A-phase coil 21a as an example.

[0072] As shown in Figure 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.

[0073] 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 144a. 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 144a. The negative terminal AN of coil 21a (or BN of coil 21b) is connected to the node where transistors Q1 and Q2 are commonly connected, and the positive terminal AP of coil 21a (or BP of coil 21b) is connected to the node where transistors Q3 and Q4 are commonly connected.

[0074] 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.

[0075] 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.

[0076] 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.

[0077] 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. For example, as shown in Figure 4A, by turning off transistors Q1 and Q4 and turning on transistors Q2 and Q3, current flows from the positive terminal AP side of coil 21a to the negative terminal AN side of coil 21a, and coil 21a 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 side of coil 21a to the positive terminal AP side of coil 21a, and coil 21a is excited in the negative direction.

[0078] Next, I will explain the attenuation modes. The damping mode is an operating mode that dampens the coil current of coil 21. In this embodiment, the damping mode includes a low-speed damping mode that regenerates the coil current, a high-speed damping mode that regenerates the coil current at a faster rate than the low-speed damping mode, and a mixed damping mode that regenerates the coil current by combining the low-speed damping mode and the high-speed damping mode.

[0079] Figure 4B is a diagram illustrating the low-speed damping mode. For example, when attenuating the current in coil 21a that was excited in the positive direction by the charge mode, the slow attenuation mode turns off transistors Q1 and Q3 and turns on transistors Q2 and Q4 in the inverter circuit 143a. As a result, as shown in Figure 4B, the current in coil 21a can be regenerated to the ground potential GND side and attenuated. Similarly, when attenuating the current in coil 21a that was excited in the negative direction, the attenuation mode turns off transistors Q1 and Q3 and turns on transistors Q2 and Q4, thereby regenerating the current in coil 21a to the ground potential GND side and attenuating it.

[0080] Figure 4C is a diagram illustrating the fast damping mode. For example, when attenuating the current in coil 21a, which was excited in the positive direction by the charge mode, the high-speed attenuation mode turns off transistors Q2 and Q3 in the inverter circuit 143a and turns on transistors Q1 and Q4. As a result, as shown in Figure 4C, the current in coil 21a can be regenerated to the power supply voltage VDD side. At this time, since coil 21a is excited in the opposite direction (negative) to the previous excitation direction (positive), the current in coil 21a can be attenuated faster than in the low-speed attenuation mode.

[0081] When attenuating the current in coil 21a, 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 143a. This allows the current in coil 21a to be regenerated to the power supply voltage VDD side. At this time, since coil 21a is excited in the opposite direction (positive) to the previous excitation direction (negative), the current in coil 21a can be attenuated faster than in the low-speed attenuation mode.

[0082] The PWM signal generation unit 128 generates a drive control signal Sd based on the excitation mode specified by the excitation mode specification unit 124.

[0083] For example, if a charge mode is specified in which coil 21 is excited in the positive direction, the PWM signal generation 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 Figure 4A.

[0084] On the other hand, if the low-speed attenuation mode is specified after the coil 21 is excited in the positive direction, the PWM signal generation unit 128 generates a drive control signal Sd that turns on transistors Q2 and Q4 and turns off transistors Q1 and Q3, as shown in Figure 4B. Also, if the high-speed attenuation mode is specified after the coil 21 is excited in the positive direction, the PWM signal generation unit 128 generates a drive control signal Sd that turns on transistors Q1 and Q4 and turns off transistors Q2 and Q3, as shown in Figure 4C.

[0085] When the coil 21 is excited in the negative direction, the PWM signal generation unit 128 generates drive control signals Sda and Sdb according to the specified excitation mode so that the current flows in the opposite direction to the negative excitation case described above.

[0086] The excitation mode is specified by the excitation mode specification unit 124. Specifically, the excitation mode designation unit 124 determines the excitation mode for each PWM period based on the comparison result Scm from the comparison unit 121. For example, at the start of one PWM period for phase A, the excitation mode designation unit 124 outputs excitation mode designation information Sma, which specifies the excitation mode for the phase A coil 21a, based on the comparison result between the measured value Sia of the coil current Ia and the current reference value Sisa from the comparison unit 121. Also, at the start of one PWM period for phase B, the excitation mode designation unit 124 outputs excitation mode designation information Smb, which specifies the excitation mode for the phase B coil 21b, based on the comparison result between the measured value Sib of the coil current Ib and the current reference value Sisb from the comparison unit 121.

[0087] 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 denoted as "excitation mode designation information Sm".

[0088] When the comparison result of the comparison unit 121 is at the first logic level (high level), that is, when the measured value Si of the coil current is lower than the current reference value Sis, the excitation mode designation unit 124 outputs excitation mode designation information Sm designating the charge mode as the excitation mode.

[0089] On the other hand, when the comparison result of the comparison unit 121 is at the second logic level (low level), that is, when the measured value Si of the coil current is equal to or higher than the current reference value Sis, the excitation mode designation unit 124 outputs excitation mode designation information Sm designating the attenuation mode as the excitation mode.

[0090] 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. When the measured value Si of the current has not reached the current reference value Sis (Si < Sis), the excitation mode designation unit 124 designates the charge mode as the excitation mode. Then, within that PWM cycle, when the measured value Si of the current reaches the current reference value Sis, the excitation mode designation unit 124 switches the excitation mode from the charge mode to the attenuation mode and maintains the attenuation mode until the end of that PWM cycle.

[0091] Here, the motor drive control device 10 may have a function in which the excitation mode becomes the charge mode at least once in each PWM cycle. For example, a minimum time Tmin for designating the minimum value of the length of the charge mode period in each PWM cycle may be set in the motor drive control device 10. Information on the minimum time Tmin is set in the storage unit 123 in advance, for example.

[0092] For example, even if the measured current Si has already reached the current reference value Sis (Si ≥ Sis) at the start of one PWM cycle, the excitation mode specification unit 124 outputs excitation mode specification information Sm that specifies the charge mode as the excitation mode for at least a period equivalent to the minimum time Tmin, regardless of the comparison result of the comparison unit 121.

[0093] For example, the excitation mode designation unit 124 first designates the charge mode as the excitation mode after the start of one PWM cycle. After designating the charge mode, the excitation mode designation unit 124 measures the duration Ton of the charge mode, and when the duration Ton reaches the minimum time Tmin, it switches the excitation mode from the charge mode to the attenuation mode. Subsequently, the excitation mode designation unit 124 maintains the attenuation mode until the end of the PWM cycle.

[0094] Furthermore, if the charge mode is specified as the excitation mode, and the measured current Si reaches the current reference value Sis before the charge mode period reaches the minimum time Tmin (i.e., the comparison result Scm becomes the second logic level (low level)), the excitation mode specification unit 124 will continue the charge mode until the charge mode period Ton reaches the minimum time Tmin.

[0095] Thus, within each PWM cycle, the excitation mode becomes the charge mode for at least a period corresponding to the minimum time Tmin.

[0096] Here, the minimum time Tmin of the charge mode period in the PWM period is, for example, a time corresponding to 10% or less of the PWM period, and preferably a time corresponding to 7.5% of the PWM period.

[0097] The PWM signal generation unit 128 outputs a drive control signal Sd that instructs the on / off pattern of the transistors Q1 to Q4 described above so that the coils 21a and 21b of each phase are in an excited state corresponding to the specified excitation mode, according to the excitation mode specified by the excitation mode specification unit 124.

[0098] Figure 5 is a timing chart showing the temporal changes in the motor coil current and the drive control signal.

[0099] Figure 5 shows the waveforms of the coil current Ia and the voltage (coil voltage) of the A-phase coil 21a, viewed from top to bottom of the page.

[0100] In the motor drive control device 10 according to this embodiment, the current reference value setting unit 122 alternately repeats 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, for each coil 21a, 21b to be driven (each phase). Then, as described above, the excitation mode designation unit 124 designates an excitation mode so that the measured value of the current Si does not exceed the current reference value Sis, and the PWM signal generation unit 128 generates drive control signals Sda and Sdb corresponding to the designated excitation mode. As a result, as shown in Figure 5, the coil currents Ia and Ib of each phase are controlled to be sinusoidal.

[0101] Figure 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 to be 90 degrees shifted from the phase of the current Ia in the A-phase coil 21a.

[0102] As described above, the excitation mode designation unit 124 switches the excitation mode for each PWM cycle during the current increase period TI and the current decay period TD, based on the comparison result between the measured coil current Si and the current reference value Sis, using the method described above.

[0103] On the other hand, the excitation mode designation unit 124 may differentiate the damping mode during the current increase period TI from the damping mode during 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 low-speed damping mode as the damping mode during the current increase period TI. That is, during the current increase period TI, either the charge mode or the low-speed damping mode is selected as the excitation mode. The excitation mode designation unit 124 also selects the mixed damping mode as the damping mode during the current decay period TD. That is, during the current decay period TD, either the charge mode or the mixed damping mode is selected as the excitation mode. The damping modes during the current decay period TD will be described in detail below.

[0104] Figure 6 is an enlarged view of a portion of the current decay period TD in Figure 5.

[0105] As shown in Figure 6, 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).

[0106] The lengths of the first decay period Td1 and the second decay period Td2 are, for example, predetermined. For instance, the period from when the electrical angle θ is 90° to 120° (270° to 300°) is set as the first decay period Td1, and the period from when the electrical angle θ is 120° to 180° (300° to 360°) is set as the second decay period Td2.

[0107] The excitation mode selection unit 124 selects the low-speed decay mode as the decay mode for the first decay period Td1 and the mixed decay mode as the decay mode for the second decay period Td2.

[0108] Figure 7 shows an example of the temporal change in coil current during the first decay period Td1.

[0109] In the figure, the horizontal axis represents time t and the vertical axis represents current. Reference numeral 500 represents the temporal change of the current in coil 21 (measured value Si of the current in coil 21). Further, FIG. 7 shows a case where the current reference value Sis is set to “Ith2” in the first PWM cycle from time t0 to time t2, and the current reference value Sis is set to “Ith1 (<Ith2)” in the PWM cycles after time t2.

[0110] As shown in FIG. 7, at time t0 when one PWM cycle starts, the excitation mode designating unit 124 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 coil 21 has not reached the current reference value Sis (= Ith2), the excitation mode designating unit 124 sets the excitation mode to the charge mode (see FIG. 4A). Thereby, the current in coil 21 increases.

[0111] Thereafter, when the measured value Si of the current reaches the current reference value Sis (= Ith2) at time t1, the excitation mode designating unit 124 switches the excitation mode from the charge mode to the low-speed decay mode (decay mode) and maintains the low-speed decay mode until time t2 when the next PWM cycle starts.

[0112] Then, at time t2 when a new PWM cycle starts, the excitation mode designating unit 124 compares the measured value Si of the current with the current reference value Sis (= Ith1). As shown in FIG. 7, at time t2, since the measured value Si of the current is higher than the current reference value Sis (= Ith1), the excitation mode designating unit 124 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 cycle starts.

[0113] Thus, in the first decay period Td1 during the current decay period TD, the low-speed decay mode is selected as the decay mode.

[0114] FIG. 8 is a diagram showing an example of the temporal change of the coil current in the second decay period Td2.

[0115] In FIG. 8, the horizontal axis represents time t and the vertical axis represents current. Reference numeral 501 represents the temporal change of the current in coil 21 (measured value Si of the current in coil 21). Also shown in FIG. 8 is a case where 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.

[0116] As shown in FIG. 8, the excitation mode specifying unit 124 selects a mixed decay mode as the decay mode in the remaining second decay period Td2 of the current decay period TD.

[0117] Specifically, when the excitation mode specifying unit 124 decays the coil current by the mixed decay mode, in the decay period Tdd for decaying the coil current within one PWM period, first one of the low-speed decay mode and the high-speed decay motor is specified, and then the other of the low-speed decay mode and the high-speed decay motor is specified. For example, FIG. 8 illustrates a case where the low-speed decay mode is specified first and then the high-speed decay mode is specified in the decay period Tdd of each PWM period. Also shown in FIG. 8 is a case where the low-speed decay mode and the high-speed decay mode are each specified once in the decay period Tdd.

[0118] When one PWM period starts, the excitation mode specifying unit 124 specifies the charge mode as the excitation mode and starts measuring the length of the period Ton of the charge mode. Then, when the excitation mode specifying unit 124 detects that the measured value Si of the current in coil 21 has reached the current reference value Sis and the measurement time of the period Ton of the charge mode is not less than the minimum time Tmin, the excitation mode is switched from the charge mode to the decay mode.

[0119] For example, as shown in Figure 8, at time t0 when the PWM cycle begins, the excitation mode designation unit 124 first sets the excitation mode to charge mode and starts measuring time to measure the length of the charge mode period Ton. As a result, the current in the coil 21 increases (see Figure 4A).

[0120] Subsequently, at time t1, when the measured current Si reaches the current reference value Sis (=Ith2) and the measurement time of the charge mode period Ton is detected to be equal to or greater than the minimum time Tmin set in the memory unit 123, the excitation mode designation unit 124 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 8 (see Figure 4B).

[0121] Here, the duration T1 of the slow decay mode is determined by a specified time Tf1 that specifies the length of the duration T1 of the slow decay mode, which is stored in the memory unit 123. For example, when the PWM period is T, the duration of the charge mode is Ton, the decay period is Tdd, and the specified time Tf2 specifies the length of the duration T2 of the fast decay mode, the specified time Tf1 that specifies the length of the duration T1 of the slow decay mode is expressed by the following equation (1).

[0122]

number

[0123] For example, when the charge mode ends, the excitation mode designation unit 124 updates the designated time Tf1 based on the above equation (1) and sets the excitation mode to the low-speed decay mode. Then, after setting the excitation mode to the low-speed decay mode, the excitation mode designation unit 124 starts measuring the length of the period T1 in the low-speed decay mode.

[0124] Subsequently, at time tc1, when the measurement time for the low-speed decay mode period T1 reaches the specified time Tf1, the excitation mode designation unit 124 switches the excitation mode from the low-speed decay mode to the high-speed decay mode and maintains the high-speed decay mode until time t2, when the next PWM cycle begins. As a result, the high-speed decay mode continues for a period corresponding to the specified time Tf2, and the current in the coil 21 decreases at a steeper rate than in the low-speed decay mode (see Figure 4C).

[0125] Similarly, from time t2 onward in Figure 8, the excitation mode is switched between the charge mode and the mixed decay mode with each PWM cycle.

[0126] In this case, when the coil current is attenuated by a mixed attenuation mode, the proportion of the fast attenuation mode period T2 within the attenuation period Tdd of one PWM period is dynamically changed.

[0127] Specifically, the excitation mode designation unit 124, when it detects that the measured value Si of the coil current has reached the current reference value Sis in the mixed decay mode, performs an increase process to make the ratio of the fast decay mode period T2 in the decay period Tdd within the PWM period (T2 / Tdd) larger than the ratio of the fast decay mode period T2 in the decay period Tdd within the previous PWM period.

[0128] For example, the excitation mode designation unit 124 performs an increment process when it detects that the charge mode period Ton in the PWM period matches the minimum time Tmin (Ton = Tmin).

[0129] The fact that the charge mode period Ton in the PWM cycle coincides with the minimum time Tmin indicates that the coil current (measured value Si of the coil current) has already reached the current reference value Sis before the minimum time Tmin has elapsed. In other words, in this case, sufficient coil current is supplied to generate the torque required for the motor, so it is necessary to rapidly decay the coil current during the current decay period TD, which is required to change the coil current sinusoidally. For this reason, it is preferable to lengthen the period of the fast decay mode in the mixed decay mode.

[0130] Therefore, 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 ratio of the fast decay mode period T2 in the decay period Tdd within the PWM period greater than the ratio of the fast decay mode period T2 in the decay period Tdd within the previous PWM period.

[0131] More specifically, each time the excitation mode designation unit 124 detects that the measured value Si of the coil current 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 period by a unit increase time ΔT.

[0132] The unit increase time ΔT is information that specifies the amount of increase in the duration of the high-speed 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 corresponds to a time of 10% or less of the PWM period.

[0133] Here, an upper limit time Tlmt may be set to specify the upper limit of the length of the fast decay mode period T2. For example, each time the excitation mode designation 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 period by a unit increase time ΔT up to the upper limit time Tlmt.

[0134] Information regarding 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).

[0135] Here, we will explain the process for increasing the duration of the fast decay mode in the mixed decay mode.

[0136] Figure 9 is a flowchart showing an example of an increment process flow that increases the duration of the fast decay mode in the mixed decay mode.

[0137] For example, at the start of a new PWM cycle, the excitation mode designation unit 124 determines whether the charge mode period Ton in the previous PWM cycle matches the minimum time Tmin (step S1).

[0138] If the charge mode period Ton does not match the minimum time Tmin (step S1: NO), the excitation mode designation unit 124 switches the excitation mode based on the comparison result between the coil current and the current reference value using the method described above, without performing an increase process.

[0139] On the other hand, if the charge mode period Ton matches the minimum time Tmin (step S1: YES), the excitation mode designation unit 124 starts the incrementing process. First, the excitation mode designation unit 124 obtains a designated time Tf2 that specifies the length of the fast decay mode period T2 (step S2). For example, the designated time Tf2 for the fast decay mode is stored in the storage unit 123. The excitation mode designation unit 124 reads the designated time Tf2 from the storage unit 123.

[0140] Next, the excitation mode designation unit 124 adds the unit increase time ΔT (for example, a time equivalent to 10% of the PWM period) read from the storage unit 123 to the specified time Tf2 of the high-speed decay mode read in step S2 (step S3). As a result, the excitation mode designation unit 124 obtains an added value (Tf2 + ΔT) by adding ΔT to Tf2.

[0141] Next, the excitation mode designation unit 124 determines whether the added value (Tf2 + ΔT) is greater than or equal to the upper limit time Tlmt stored in the storage unit 123 (step S4). If the added value (Tf2 + ΔT) is less than the upper limit time Tlmt (step S4: NO), the excitation mode designation unit 124 updates the designated time Tf2 for the high-speed decay mode stored in the storage unit 123 to the added value (Tf2 + ΔT) (step S5). As a result, the designated time Tf2 for the high-speed decay mode becomes (Tf2 + ΔT), and the increment process ends.

[0142] On the other hand, if the added value (Tf2 + ΔT) is greater than or equal to the upper limit time Tlmt (step S4: YES), the excitation mode designation unit 124 updates the designated time Tf2 of the high-speed decay mode stored in the memory unit 123 to the upper limit time Tlmt (step S6). As a result, the designated time Tf2 of the high-speed decay mode becomes Tlmt, and the increment process ends.

[0143] The above procedure increases the duration of the high-speed decay mode.

[0144] Next, we will explain the process of increasing the duration of the fast decay mode using Figure 8. For example, when a new PWM period (the PWM period from time t2 to time t4) starts at time t2 in FIG. 8, the excitation mode designating unit 124 compares the period Ton of the charge mode in the previous PWM period with the minimum time Tmin. As shown in FIG. 8, the period Ton of the charge mode in the previous PWM period, that is, the PWM period from time t0 to time t2, is longer than the minimum time Tmin. Therefore, the excitation mode designating unit 124 does not perform the above-described increase process. Then, the excitation mode designating unit 124 switches the excitation mode based on the comparison result Scm by the above-described method in the PWM period from time t2 to time t4.

[0145] Thereafter, when a new PWM period (the PWM period from time t4 to time t6) starts at time t4, the excitation mode designating unit 124 compares the period Ton of the charge mode in the previous PWM period with the minimum time Tmin. As shown in FIG. 8, the period Ton of the charge mode in the previous PWM period, that is, the PWM period from time t2 to time t4, coincides with the minimum time Tmin. Therefore, the excitation mode designating unit 124 performs the increase process. That is, the excitation mode designating unit 124 sets, in the storage unit 123, an added value (Tf2 + ΔT) obtained by adding the unit increase time ΔT to the designated time Tf2 of the high-speed attenuation mode stored in the storage unit 123 as the designated time (<Tlmt) of the new high-speed attenuation mode. As a result, as shown in FIG. 8, the period T2 of the high-speed attenuation mode in the PWM period from time t4 to time t6 becomes longer by ΔT than the period T2 of the high-speed attenuation mode in the PWM period from time t previous t2 to time t4.

[0146] As described above, the motor drive control device 10 dynamically changes the period T2 of the high-speed attenuation mode in the hybrid attenuation mode for each PWM period.

[0147] Note that, in the above example, the case where the increase process is performed at the timing when one PWM period starts is shown. However, the increase process may be performed for each one PWM period or for a plurality of PWM periods, and the timing at which the increase process starts is not particularly limited.

[0148] Next, the effects of the motor drive control device 10 according to the embodiment will be described.

[0149] Figure 10A shows the measured coil current when a motor is driven by a motor drive control device according to a prior art study by the present inventor, which serves as a comparative example.

[0150] Figure 10B shows the measured coil current when the motor is driven by the motor drive control device 10 according to the embodiment.

[0151] Figures 10A and 10B show the waveforms of the A-phase coil current Ia of the motor, respectively.

[0152] The motor drive control device according to the prior study differs from the motor drive control device 10 according to the embodiment in that it fixes the period of the high-speed damping mode in the mixed damping mode, but is otherwise the same as the motor drive control device 10 according to the embodiment.

[0153] As shown in Figure 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 Figure 5), and the coil current may not be able to change sinusoidally.

[0154] In contrast, the motor drive control device 10 according to this embodiment dynamically changes the duration of the high-speed decay mode in the mixed decay mode according to the 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 make the ratio of the high-speed decay mode period T2 in the decay period Tdd within the PWM cycle greater than the ratio of the high-speed decay mode period T2 in the decay period Tdd within the previous PWM cycle.

[0155] According to this, as shown in Figure 10B, the coil current can be sufficiently attenuated during the current decay period for changing the coil current into a sinusoidal shape, making it possible to bring the waveform of the coil current closer to a sinusoidal wave.

[0156] Furthermore, according to the motor drive control device 10 of this embodiment, the mixed damping mode can generate both gradual and steep damping of the coil current. This reduces the change in current caused by the switching of damping modes during the current damping period TD, thereby reducing the distortion of the sinusoidal coil current and suppressing the generation of abnormal noise during motor operation.

[0157] Thus, according to the motor drive control device 10 of this embodiment, it is possible to appropriately control the coil current of the motor while suppressing the generation of abnormal noise during motor operation.

[0158] Furthermore, the motor drive control device 10 according to the embodiment performs an increment process when it detects that the charge mode period Ton in the PWM period matches the minimum time Tmin which specifies the minimum length of the charge mode period Ton. This makes it easy to detect whether or not the coil current has reached a current reference value.

[0159] Furthermore, the motor drive control device 10 according to the embodiment is set to a unit increase time ΔT that specifies the amount of increase in the period of the high-speed decay mode. The motor drive control device 10 performs the increase process for each PWM period, and in the increase process, increases the period of the high-speed decay mode in the decay period Tdd within the PWM period by the unit increase time ΔT. According to this, the proportion of the high-speed decay mode period T2 within the decay period Tdd of the PWM cycle can be gradually increased with each PWM cycle, thereby achieving stable motor drive control. Furthermore, by setting the unit increase time ΔT to an appropriate value according to the application to which actuator 1 is applied, stable motor drive control can be achieved for each application.

[0160] Furthermore, the motor drive control device 10 according to the embodiment is set to an upper limit time Tlmt, which indicates the upper limit of the length of the high-speed decay mode period. The motor drive control device 10 increases the period T2 of the high-speed decay mode in the decay period Tdd within the PWM period by a unit increase time ΔT up to the upper limit time Tlmt by performing an increment process each time it detects that the coil current has reached a current reference value. According to this, by setting an appropriate upper limit for the period T2 of the high-speed damping mode according to the application to which actuator 1 is applied, it becomes possible to achieve stable motor drive control for each application.

[0161] <<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.

[0162] For example, in the above embodiment, when the coil current is attenuated by a mixed attenuation mode, Figure 8 shows an example where the low-speed attenuation mode is specified at the beginning of the attenuation period Tdd of each PWM cycle, followed by the high-speed attenuation mode. However, the order in which the attenuation modes are specified in the mixed attenuation mode is not particularly limited. For example, in the attenuation period Tdd, the high-speed attenuation mode may be specified first, followed by the low-speed attenuation mode.

[0163] Furthermore, while Figure 8 illustrates a case where the slow-speed decay mode and the fast-speed decay mode are specified once each during the decay period Tdd within a single PWM cycle, the number of times the slow-speed decay mode and the fast-speed decay mode are specified during the decay period Tdd is not particularly limited. For example, the slow-speed decay mode and the fast-speed decay mode may be alternately repeated multiple times during the decay period Tdd.

[0164] Furthermore, 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.

[0165] 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]

[0166] 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, 120…Current value acquisition unit, 121…Comparison unit, 122…Current reference value setting unit, 123…Storage unit, 124…Excitation mode specification 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 sensors, AP, BP...positive terminals of coil 21, AN, BN...negative terminals of coil 21, Q1~Q4...transistors, D1~D4...diodes, Ia, Ib...coil current, Scm, Scma, Scmb...comparison results, Sd, Sda, Sdb...drive control signals, Si, Sia, Sib...measured values ​​of coil current, Sis, Sis1, Sis2...current reference values, T1...duration of slow decay mode, T2...duration of fast decay mode, Tdd...decay period within the PWM cycle, Tf1...specified time for the slow decay mode period, Tf2...specified time for the fast decay mode period, ΔT...unit increase time, Tlmt...upper limit time, Tmin...minimum time, Ton...duration of charge mode, Via, Vib...current detection signals.

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 coil current, which is the current flowing through 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 coil 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, for each PWM cycle, designates a charge mode to increase the coil current when the measured value of the coil current measured by the current value acquisition unit is lower than the current reference value, and designates an attenuation mode to decrease the coil current when the measured value of the coil current is equal to or greater than the current reference value, as the excitation mode. The damping modes include a low-speed damping mode for regenerating the coil current, a high-speed damping mode for regenerating the coil current at a higher speed than the low-speed damping mode, and a mixed damping mode for regenerating the coil current by combining the low-speed damping mode and the high-speed damping mode. When the excitation mode designation unit attenuates the coil current by the mixed attenuation mode, in the attenuation period during which the coil current is attenuated within one PWM cycle, it first designates one of the low-speed attenuation mode and the high-speed attenuation mode, and then designates the other of the low-speed attenuation mode and the high-speed attenuation mode. 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 fast decay mode period within the decay period in the PWM cycle greater than the proportion of the fast decay mode period within the decay period in the previous PWM cycle. Motor drive control device.

2. In the motor drive control device according to claim 1, The system further includes a storage unit that stores a minimum time that specifies the minimum length of the charge mode period in the PWM cycle, The excitation mode designation unit performs the increase process when it detects that the duration of the charge mode in the PWM cycle is the minimum time. Motor drive control device.

3. In the motor drive control device according to claim 2, The excitation mode designation unit performs the incrementing process for each PWM cycle. The storage unit stores a unit increase time that specifies the amount of increase in the period of the high-speed decay mode. The excitation mode designation unit, in the increase process, increases the duration of the high-speed decay mode during the decay period within the PWM cycle by the unit increase time. Motor drive control device.

4. In the motor drive control device according to claim 3, The storage unit stores an upper limit time indicating the upper limit of the duration of the high-speed decay mode. The excitation mode designation unit, each time it detects that the coil current has reached the current reference value, increases the duration of the high-speed decay mode within the decay period of the PWM cycle by the unit increment time up to the upper limit time. Motor drive control device.

5. In the motor drive control device according to claim 4, The excitation mode designation unit designates the low-speed decay mode as the decay mode for the first decay period, which is the first period in the current decay period during which the current reference value changes toward zero, and the mixed decay mode as the decay mode for the second decay period, which is the remaining period after the first decay period in the current decay period. Motor drive control device.

6. The motor and, A motor drive control device as described in any one of claims 1 to 5, An actuator comprising a power transmission mechanism for transmitting the rotational force of the motor to a drive object.

7. 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 coil current at each PWM period of the PWM signal, such that the coil current, which is the current flowing through the coil, is sinusoidal. The motor drive control device includes a third step in which, for each PWM cycle, if the measured value of the coil current is lower than the current reference value, a charge mode is designated as the excitation mode to increase the coil current, and if the measured value of the coil current is equal to or greater than the current reference value, a damping mode is designated as the excitation mode to decrease the coil current. The damping modes include a low-speed damping mode for regenerating the coil current, a high-speed damping mode for regenerating the coil current at a higher speed than the low-speed damping mode, and a mixed damping mode for regenerating the coil current by combining the low-speed damping mode and the high-speed damping mode. The previous third step is, When the motor drive control device attenuates the coil current by the mixed attenuation mode, a fourth step is to first specify one of the low-speed attenuation mode and the high-speed attenuation mode, and then specify the other of the low-speed attenuation mode and the high-speed attenuation mode during the attenuation period in which the coil current is attenuated within one PWM cycle, The motor drive control device includes a fifth step in which, when it 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 fast decay mode period in the decay period within the PWM cycle greater than the proportion of the fast decay mode period in the decay period within the previous PWM cycle. Motor drive control method.

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