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

Abstract

To increase the rotation speed of a motor without reducing safety in operation of the motor.SOLUTION: In a motor drive control device 5, a control circuit 6 comprises: a zero cross detection section 61 which detects a zero cross of a counter electromotive voltage generated in a coil 4 of a non-electrification phase of a motor 2; a delay time setting section 67 which sets a delay time Td in the case of commutation of the coil 4; a drive control signal generation section 69 which generates a drive control signal Sd so as to perform the commutation of the coil 4 after the lapse of the delay time Td from the detection of the zero cross; and an operation state monitor section 62 which monitors an operation state of the motor 2. The delay time setting section 67 sets the delay time Td to a reference value T0 and, when it is detected that the operation state of the motor 2 satisfies a predetermined condition, makes the delay time Td shorter than the reference value T0.SELECTED DRAWING: Figure 3

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 a stepping motor (hereinafter also simply referred to as "motor") for driving an air conditioner or the like in an HVAC (Heating Ventilation and Air-Conditioning) system as an in-vehicle air conditioning unit, a method of performing commutation of the coil in accordance with detection of the zero crossing of the back electromotive voltage of the coil of the motor is known (see Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] According to the method of performing commutation of the coil in accordance with detection of the zero crossing of the back electromotive voltage of the coil in the motor, the rotation speed of the motor increases as the load becomes lighter, and the motor is driven so that the rotation speed decreases as the load becomes heavier. Therefore, the motor can be rotated at an appropriate torque and rotation speed according to the load of the motor.

[0005] By the way, in order to make the driving of the motor more stable by the above method, a delay time may be set when switching the commutation of the coil. That is, instead of immediately performing the commutation of the coil after detecting the zero crossing of the back electromotive voltage, the commutation of the coil is performed after a predetermined time (delay time) has elapsed since the zero crossing of the back electromotive voltage was detected.

[0006] By increasing the delay time during commutation, the torque becomes larger, so the occurrence of detuning can be suppressed and the operation of the motor can be stabilized. On the other hand, if the delay time during commutation is longer than half of the period of the current waveform from the zero crossing, the rotational speed of the motor becomes slower, and the time required to rotate the motor to the target rotational position becomes longer. Therefore, it is necessary to preset the value of the delay time for each system in consideration of the rotational speed and stability of the motor required for each system to which the motor is applied.

[0007] However, even if the system to which the motor is applied is the same, the operating conditions of the motor may change due to load fluctuations or the like, so it is not easy to find out the optimal delay time during commutation in advance. For example, in the manufacturing stage or inspection stage of the actuator 1, there may be a case where after applying grease to the driving part (such as a gear) of the actuator, the motor is operated by a predetermined amount to make the grease conform. When performing this process, since the load on the motor is in the lightest state, it is preferable to end the above process in as short a time as possible by shortening the delay time during commutation. On the other hand, after the introduction of the HVAC system, since the load on the motor fluctuates, if the delay time is shortened, detuning or the like may occur, and the operation of the motor may become unstable.

[0008] The present invention has been made in view of the above-described problems, and an object thereof is to increase the rotational speed of a motor without impairing the stability of the operation of the motor.

Means for Solving the Problems

[0009] A motor drive control device according to a representative embodiment of the present invention includes a control circuit that generates a drive control signal for controlling the drive of a motor having a plurality of phase coils, a drive circuit that drives the coils based on the drive control signal, and a voltage detection circuit that detects the voltage of the coils. The control circuit includes a zero-cross detection unit that detects a zero-cross of a back electromotive voltage generated in the non-energized phase coil based on the voltage detected by the voltage detection circuit, a delay time setting unit that sets a delay time during commutation of the coil, a drive control signal generation unit that generates the drive control signal so as to perform commutation of the coil after the elapse of the delay time since the zero-cross is detected by the zero-cross detection unit, and an operation state monitoring unit that monitors an operation state of the motor. The delay time setting unit sets the delay time to a reference value, and shortens the delay time from the reference value when it is detected that the operation state satisfies a predetermined condition based on a monitoring result by the operation state monitoring unit.

Advantages of the Invention

[0010] According to the motor drive control device of the present invention, it is possible to increase the rotational speed of the motor without impairing the stability of the operation of the motor.

Brief Description of the Drawings

[0011]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5A

Figure 5B

Figure 6

Embodiments for Carrying Out the Invention

[0012] 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 given to the common components in each embodiment, and repeated descriptions are omitted. Also, note that the drawings are schematic, and it is necessary to be aware that the dimensional relationships between elements, the ratios of the elements, etc. may be different from reality. There may also be parts where the dimensional relationships and ratios are different between the drawings.

[0013] 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.

[0014] 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.

[0015] In the HVAC system, the actuator 1 is connected to the ECU as the upper device 10 described later via a bus together with other actuators, for example, to form a LIN (Local Interconnect Network) communication network.

[0016] As shown in FIG. 1, the actuator 1 is covered by a case 12 and a cover 13. Inside the actuator 1, there are a motor 2, a motor drive control device 5 that controls the drive of the motor 2, and a primary gear 15, a secondary gear 16, a tertiary gear 17, and an output gear 18 as a power transmission mechanism that transmits the rotational force of the output shaft 14 of the motor 2 to the object to be driven.

[0017] The motor 2 generates the driving force of the actuator 1. The motor 2 is, for example, a stepping motor. In the present embodiment, the motor 2 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 2 operates when drive power is supplied from the motor drive control device 5 to the coils of each phase.

[0018] FIG. 2 is a diagram schematically showing the configuration of the motor 2 and the motor drive control device 5.

[0019] As described above, the motor 2 is a two-phase stepping motor. As shown in FIG. 2, the motor 2 has, for example, a rotor 3, a phase A coil 4a, a phase B coil 4b, and a two-phase stator (not shown).

[0020] The coils 4a and 4b are elements that excite the stator (not shown), respectively. The coil 4a has a positive terminal AP and a negative terminal AN as motor terminals 19. The coil 4b has a positive terminal BP and a negative terminal BN as motor terminals 19. The terminal AP and the terminal AN of the coil 4a, and the terminal BP and the terminal BN of the coil 4b are respectively connected to inverter circuits 9a and 9b that constitute the drive circuit 8. Details of the inverter circuits 9a and 9b will be described later.

[0021] The coils 4a and 4b are driven by the inverter circuits 9a and 9b. As a result, currents Ia and Ib having different phases flow through the coils 4a and 4b. For example, currents Ia and Ib having phases shifted by 90 degrees from each other flow through the coils 4a and 4b.

[0022] In the following description, when the coil 4a and the coil 4b are not distinguished, they are simply referred to as "coil 4".

[0023] The rotor 3 includes a permanent magnet magnetized with a single pole or multiple poles such that the S pole 3S and the N pole 3N alternate and reverse along the circumferential direction. In FIG. 2, as an example, the case where the rotor 3 has two poles is shown.

[0024] The stator (not shown) is disposed around the rotor 3 and close to the outer peripheral portion of the rotor 3. The rotor 3 rotates when the phases of the coil currents flowing through the coils 4a and 4b are periodically switched. An output shaft 14 is connected to the rotor 3, and the output shaft 14 is driven by the rotational force of the rotor 3.

[0025] As shown in FIG. 1, a primary gear 15 is attached to the output shaft 14 of the motor 2. The primary gear 15 of the motor 2 meshes with a secondary gear 16. The secondary gear 16 meshes with a tertiary gear 17. The tertiary gear 17 meshes with an output gear 18. On the bottom surface of the case 12, an external output gear (not shown) provided on the output gear 18 is exposed, and this external output gear is connected to a drive target.

[0026] The motor drive control device 5 is a device for driving the motor 2. The motor drive control device 5 communicates with a host device (ECU) via a bus, for example. Based on a drive command signal Sc, which is a control frame received from the host device, the motor drive control device 5 controls the energization states of the coils 4a and 4b of each phase of the motor 2 to control the rotation and stop of the motor 2, thereby controlling the operation of the entire actuator 1. When the motor drive control device 5 drives the motor 2, the primary gear 15 connected to the output shaft 14 of the motor 2 rotates. The driving force generated by the rotation of the primary gear 15 is transmitted in sequence to the secondary gear 16, the tertiary gear 17, the output gear 18, and the external output gear, and the external output gear drives a movable part of an air conditioner that is the drive target.

[0027] As shown in FIG. 1, the motor drive control device 5 has, as hardware resources, for example, a printed circuit board 21 and a flexible printed circuit board 22 that connects the printed circuit board 21 and the motor terminals 19 of the motor 2. The printed circuit board 21 is provided with a control circuit 6, a voltage detection circuit 7, a drive circuit 8, and a plurality of external connection terminals 20 shown in FIG. 2.

[0028] Note that the circuit housed inside the case 12 and the cover 13 may be only the drive circuit 8. For example, the motor drive control device 5 may be configured by a drive circuit 8 provided inside the case 12 and the cover 13 and a control circuit 6 provided outside the case 12 and the cover 13.

[0029] The voltage detection circuit 7 is a circuit that detects the voltages of the coils 4a and 4b of the motor 2. For example, the voltage detection circuit 7 respectively detects the voltages of the positive terminal AP and the negative terminal AN in the A-phase coil 4a, and converts them into voltages Vap and Van of a magnitude that can be input to the control circuit 6 and outputs them. Similarly, the voltage detection circuit 7 respectively detects the voltages of the positive terminal BP and the negative terminal BN in the B-phase coil 4b, and converts them into voltages Vbp and Vbn of a magnitude that can be input to the control circuit 6 and outputs them. The voltage detection circuit 7 is configured to include a known circuit such as a resistor voltage division circuit, for example.

[0030] Note that the voltage detection circuit 7 may have an analog / digital conversion circuit. For example, the voltage detection circuit 7 may convert the detected voltages Vap, Van, Vbp, and Vbn into digital signals and output them respectively. Also, the voltage detection circuit 7 may be provided inside the drive circuit 8.

[0031] The control circuit 6 is a circuit that generates a drive control signal Sd to control the drive of the motor 2 based on a drive command signal Sc from a host device (ECU). Here, the drive command signal Sc includes information indicating the target state of the motor 2. For example, the drive command signal Sc includes information specifying the rotational speed of the motor 2 and information specifying the target rotational angle (target rotational position) of the motor 2. The information specifying the target rotational position may be, for example, information specifying the number of drive steps (number of pulses) of the motor 2 corresponding to the amount of movement (target movement amount) to the target rotational position.

[0032] The control circuit 6 generates a drive control signal Sda for exciting the coil 4a of the A-phase of the motor 2 and a drive control signal Sdb for exciting the coil 4b of the B-phase of the motor 2 based on the back electromotive voltage of the coil 4 of the motor 2 detected by the voltage detection circuit 7, and supplies them to the drive circuit 8 respectively, thereby rotating the motor 2 to the target rotational position. 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 are denoted as "drive control signal Sd". The details of the control circuit 6 will be described later.

[0033] The drive circuit 8 controls the energization of the coil 4 of the motor 2 based on the drive control signal Sd output from the control circuit 6. The drive circuit 8 includes inverter circuits 9a and 9b for driving the coil 4 of the motor 2.

[0034] The inverter circuits 9a and 9b are circuits that supply driving power to the motor 2 based on the drive control signal Sd. As shown in FIG. 2, the inverter circuits 9a and 9b are provided corresponding to each of the coils 4a and 4b to be driven, for example. For example, as shown in FIG. 2, an inverter circuit 9a for driving the coil 4a of the A phase and an inverter circuit 9b for driving the coil 4b of the B phase are provided. The inverter circuits 9a and 9b are constituted by, for example, an H-bridge circuit. In the following description, when the inverter circuit 9a and the inverter circuit 9b are not distinguished, the inverter circuit 9a and the inverter circuit 9b may be referred to as "inverter circuit 9".

[0035] As shown in FIG. 2, the inverter circuit 9a is connected to the positive terminal AP of the coil 4a of the A phase and the negative terminal AN of the coil 4a. The inverter circuit 9b is connected to the positive terminal BP of the coil 4b of the B phase and the negative terminal BN of the coil 4b.

[0036] The inverter circuit 9a applies a voltage Va between the terminal AP and the terminal AN based on the drive control signal Sda output from the control circuit 6, thereby causing a current Ia to flow through the coil 4a. The inverter circuit 9b applies a voltage Vb between the terminal BP and the terminal BN based on the drive control signal Sdb output from the control circuit 6, thereby causing a current Ib to flow through the coil 4b.

[0037] For example, as shown in FIG. 2, during the "A-phase (+) excitation period" in which a current +Ia flows from the terminal AP to the terminal AN of the coil 4a of the A-phase, the inverter circuit 9a applies, for example, a voltage of "+Va" to the terminal AP with respect to the terminal AN of the coil 4a. On the other hand, during the "A-phase (-) excitation period" in which a current -Ia flows from the terminal AN to the terminal AP of the coil 4a of the A-phase, the inverter circuit 9a applies a voltage of "-Va" to the terminal AP with respect to the terminal AN of the coil 4a. During the "B-phase (+) excitation period" in which a current +Ib flows from the terminal BP to the terminal BN of the coil 4b of the B-phase, the inverter circuit 9b applies, for example, a voltage of "+Vb" to the terminal BP with respect to the terminal BN of the coil 4b. During the "B-phase (-) excitation period" in which a current -Ib flows from the terminal BN to the terminal BP of the coil 4b of the B-phase, the inverter circuit 9b applies a voltage of "-Vb" to the terminal BP with respect to the terminal BN of the coil 4b.

[0038] Note that the drive circuit 8 may be provided with current sensors (not shown) for detecting the currents Ia and Ib flowing through the coils 4a and 4b. For example, when a shunt resistor is provided as the current sensor, it is provided for each of the coils 4a and 4b of each phase and is connected in series with the inverter circuits 9a and 9b on the ground potential side or the power supply voltage side of the inverter circuits 9a and 9b. The current sensor on the A-phase side outputs the voltage across the shunt resistor as a current detection signal representing the measured value of the coil current Ia of the A-phase. The current sensor on the B-phase side outputs the voltage across the shunt resistor as a current detection signal representing the measured value of the coil current Ib of the B-phase.

[0039] The control circuit 6 is, for example, a program processing device (e.g., a microcontroller: MCU (Micro Control Unit)) having components (hardware elements) such as a processor like a CPU (Central Processing Unit), various memories such as a ROM (Read Only Memory) and a RAM (Random Access Memory), a timer, a counter, an A / D conversion circuit, an input / output I / F circuit, and a clock generation circuit, etc., with each component connected to each other via a bus or a dedicated line. The control circuit 6 may have a rewritable non-volatile storage device such as a flash memory or an EEPROM (Electrically Erasable Programmable Read-Only Memory) as a memory. In this embodiment, the control circuit 6 is packaged as an IC (integrated circuit) for example, but is not limited thereto. Note that the control circuit 6, the voltage detection circuit 7, and the drive circuit 8 may be packaged together.

[0040] As described above, the control circuit 6 has a current switching function for switching the energization of the coils 4a and 4b of the motor 2. Specifically, the control circuit 6 detects the zero crossing of the back electromotive voltage generated in the coil 4 of the non-excited phase of the motor 2, and after a predetermined delay time Td has elapsed, generates drive control signals Sda and Sdb so as to perform commutation of the coils 4a and 4b based on a predetermined excitation method.

[0041] Here, the predetermined excitation method may be any excitation method capable of detecting the back electromotive voltage of the coil 4, for example, a one-phase excitation method or a one-two phase excitation method. In this embodiment, the case where the predetermined excitation method is a one-phase excitation method will be taken as an example for explanation.

[0042] Furthermore, in addition to the above-described current switching function, the control circuit 6 has a delay time change function for dynamically changing the delay time Td during current switching (commutation). Hereinafter, a specific configuration example of the control circuit 6 for realizing the current switching function and the delay time change function will be described with reference to FIG. 3.

[0043] FIG. 3 is a block diagram showing the configuration of the control circuit 6 in the motor drive control device 5 according to the embodiment.

[0044] The control circuit 6 includes a zero-cross detection unit 61, an operation state monitoring unit 62, a drive control signal generation unit 69, an operation mode setting unit 66, a delay time setting unit 67, and a storage unit 68 as functional blocks for realizing a power supply switching function and a delay time changing function. These functional blocks are realized, for example, when a processor in the above-described MCU executes various operations according to a program stored in a memory and controls peripheral circuits such as a timer and a counter, an A / D conversion circuit, and an input / output I / F circuit. Note that some or all of these functional blocks may be realized by dedicated hardware circuits. Further, the control circuit 6 may have functional blocks for realizing other functions in addition to the above functions.

[0045] The storage unit 68 is a functional unit for storing data and the like necessary for motor drive control by the control circuit 6. For example, delay time information 71 and operation state information 72 are stored in the storage unit 68.

[0046] The delay time information 71 is information for determining the delay time Td at the commutation of the motor 2, and includes, for example, information on the set delay time Td, information on the unit amount Δtd representing the minimum unit at the time of changing the delay time Td, information on the reference value T0 (initial value) serving as a reference for the delay time Td, and information on the lower limit value TL which is the minimum value that can be set as the delay time Td.

[0047] The operation state information 72 is information regarding the operation state of the motor 2, and includes, for example, information on the measured rotational speed Sr of the motor 2, information on the movement amount Ms of the motor 2, information on the rotational speed threshold Sth serving as a reference for the out-of-synchronization determination, information on the first reference rotational speed Sb1 and the second reference rotational speed Sb2 serving as references when changing the delay time Td, and information on the reference movement amount Mth serving as a reference when changing the delay time Td. Details of each piece of information included in the delay time information 71 and the operation state information 72 will be described later.

[0048] The actuator 1 has a plurality of operation modes related to the drive of the motor 2. In the present embodiment, the operation modes include a normal operation mode and a test operation mode. The normal operation mode is, for example, an operation mode for driving the motor 2 (actuator 1) based on a drive command signal Sc from the host device 10 after the actuator 1 is introduced into various applications such as an HVAC system. The test operation mode (process mode) is, for example, an operation mode for test-operating the motor 2 (actuator 1) at the manufacturing stage or inspection stage of the actuator 1. For example, when performing a process of applying grease to the drive part (such as a gear) of the actuator 1 and then operating the motor by a predetermined amount to make the grease conform at the manufacturing stage or inspection stage of the actuator 1, the operation mode is set to the test operation mode.

[0049] The operation mode setting unit 66 is a functional unit for setting the operation mode. The operation mode setting unit 66, for example, sets the operation mode to the normal operation mode when the actuator 1 is started, and sets the operation mode to the test operation mode when the test operation mode is specified by the drive command signal Sc.

[0050] The zero-cross detection unit 61 is a functional unit for monitoring the voltages of the coils 4a and 4b and detecting the zero-cross of the back electromotive voltage generated in the non-excited phase coil 4.

[0051] FIG. 4 is a diagram showing an example of the temporal change of the back electromotive voltage of the coils 4a and 4b when the motor 2 is driven.

[0052] In FIG. 4, the horizontal axis represents time, and the vertical axis represents voltage. The reference numeral 400 represents the back electromotive voltage of the A-phase coil 4a, and the reference numeral 401 represents the back electromotive voltage of the B-phase coil 4b.

[0053] The zero crossing of the reverse electromotive force refers to the state in which the reverse electromotive force generated at both ends of the coil 4 of the non-excited phase (non-excitation phase) switches from positive to negative or from negative to positive. As shown in FIG. 4, during the A-phase (+) excitation period Tap and the A-phase (-) excitation period Tan when the coil 4a of the A phase is excited, the reverse electromotive force 401 of the B phase, which is the non-excited phase, can be monitored, and the point where the reverse electromotive force 401 of the B phase switches from negative to positive or from positive to negative is the zero crossing point of the reverse electromotive force of the B phase. Similarly, during the B-phase (+) excitation period Tbp and the B-phase (-) excitation period Tbn when the coil 4b of the B phase is excited, the reverse electromotive force 400 of the A phase, which is the non-excited phase, can be monitored, and the point where the reverse electromotive force 400 of the A phase switches from negative to positive or from positive to negative is the zero crossing point of the reverse electromotive force of the A phase.

[0054] The zero crossing detection unit 61 monitors the reverse electromotive force generated in the coil 4 of the non-excited phase based on the voltages Vap and Van detected by the voltage detection circuit 7. For example, during the period when the coil 4b of the B phase is excited, the zero crossing detection unit 61 monitors the voltage between the terminal AP and the terminal AN in the coil 4a of the A phase, which is the non-excited phase, as the reverse electromotive force Vapn of the coil 4a. Similarly, during the period when the coil 4a of the A phase is excited, the zero crossing detection unit 61 monitors the voltage between the terminal BP and the terminal BN in the coil 4b of the B phase, which is the non-excited phase, as the reverse electromotive force Vbpn of the coil 4b. When the zero crossing detection unit 61 detects the zero crossing (zero crossing point) of the reverse electromotive force, it outputs a zero crossing detection signal Sz indicating that the zero crossing has been detected.

[0055] The operating state monitoring unit 62 is a functional unit that monitors the operating state of the motor 2. Here, the operating state of the motor 2 refers to the rotational speed Sr of the motor 2, the moving amount Ss of the motor 2, and the presence or absence of the occurrence of out-of-step, etc.

[0056] The operating state monitoring unit 62 has, for example, a rotational speed calculation unit 64, a moving amount calculation unit 63, and an out-of-step determination unit 65.

[0057] The movement amount calculation unit 63 is a functional unit that calculates the movement amount Ms of the motor 2. In the motor 2, the unit movement amount (unit rotation angle) per drive step is a value unique to the motor and is defined in advance. Therefore, the movement amount calculation unit 63 calculates the movement amount Ms of the motor 2, for example, by multiplying the unit movement amount per drive step stored in advance in the storage unit 68 by the number of drive steps of the motor 2, stores it in the storage unit 68, and updates the movement amount Ms for each drive step. Note that the movement amount calculation unit 63 may calculate the number of drive steps of the motor 2 itself as the movement amount Ms.

[0058] The rotation speed calculation unit 64 is a functional unit that calculates (measures) the rotation speed Sr of the motor 2. The rotation speed calculation unit 64 calculates (measures) the rotation speed Sr of the motor 2 for each drive step based on the unit movement amount per drive step of the motor 2 and the time (movement time) required for the motor 2 (actuator 1) to move the unit movement amount. For example, as shown in FIG. 4, the excitation period of one phase of the motor 2 corresponds to the movement time in the unit movement amount per drive step of the motor 2. Therefore, the rotation speed calculation unit 64 calculates the rotation speed Sr of the motor 2, for example, by dividing the unit movement amount per drive step by the excitation period (A-phase excitation period Tap, Tan or B-phase excitation period Tbp, Tbn) for each drive step, and stores it in the storage unit 68. Here, the above excitation period may be calculated by measuring the interval between adjacent zero-crossing points. Note that the method for calculating the rotation speed of the motor 2 is not limited to the above example, and other known calculation methods may be adopted.

[0059] The out-of-synchronization determination unit 65 is a functional unit that determines whether or not out-of-synchronization of the motor 2 has occurred. The out-of-synchronization determination unit 65 determines that the motor 2 is out of synchronization, for example, when the rotation speed of the motor 2 is less than the rotation speed threshold Sth. Here, the rotation speed threshold Sth is set to a value smaller than the first reference rotation speed Sb1 described later. The rotation speed threshold Sth is stored in the storage unit 68 in advance, for example.

[0060] The operation state monitoring unit 62 stores information such as the rotational speed Sr of the motor 2, the movement amount Ms of the motor 2, and the presence or absence of out-of-step in the storage unit 68. Note that the operation state monitoring unit 62 may transmit information such as the rotational speed of the motor 2, the movement amount of the motor 2, and the presence or absence of out-of-step to the host device 10 as an output signal So.

[0061] The drive control signal generation unit 69 is a functional unit that generates a drive control signal Sd (Sda, Sdb). The drive control signal generation unit 69 generates and outputs the drive control signals Sda and Sdb so as to excite the coil 4a of phase A and the coil 4b of phase B at a predetermined timing based on a predetermined excitation method in order to move the rotor 3 to the target rotational position (target movement amount). Here, the predetermined excitation method is, as described above, for example, a one-phase excitation method.

[0062] When generating the drive control signal Sd by the one-phase excitation method, the drive control signal generation unit 69 generates and outputs the drive control signals Sda and Sdb so that the energization states of the coils 4a and 4b of phases A and B are switched in the order of "phase A (+) excitation period", "phase B (+) excitation period", "phase A (-) excitation period", and "phase B (-) excitation period", as shown in FIG. 4, for example.

[0063] At this time, the timing for switching the excitation phase, that is, the commutation timing of the coils 4a and 4b, is determined based on the zero-cross detection signal Sz by the zero-cross detection unit 61 and the delay time Td set by the delay time setting unit 67.

[0064] Specifically, the drive control signal generation unit 69 generates a drive control signal Sd so as to perform commutation of the coils 4a and 4b after the elapse of a delay time Td from when the zero-cross detection unit 61 detects the zero-cross of the back electromotive voltage of the coils 4a and 4b. For example, as shown in FIG. 4, in the A-phase (+) excitation period Tap, after the elapse of the delay time Td from when the zero-cross of the back electromotive voltage of the non-excited phase, i.e., the B phase, is detected, drive control signals Sda and Sdb are generated so that the excitation phase switches from the A phase to the B phase. Similarly, in the B-phase (+) excitation period Tbp in which the coil 4b of the B phase is excited, after the elapse of the delay time Td from when the zero-cross of the back electromotive voltage of the non-excited phase, i.e., the A phase, is detected, drive control signals Sda and Sdb are generated so that the excitation phase switches from the B phase to the A phase. In this way, the drive control signal generation unit 69 performs commutation of the coils 4a and 4b every time the zero-cross of the back electromotive voltage of the coil of the non-excited phase is detected and the delay time Td elapses.

[0065] The delay time setting unit 67 is a functional unit that sets the delay time Td during commutation of the coil 4 of the motor 2. The delay time setting unit 67 sets, for example, a reference value T0 as the initial value of the delay time Td after the activation of the actuator 1 (motor drive control device 5). The reference value T0 is, for example, stored in advance in the storage unit 68. When the delay time setting unit 67 detects that the operating state of the motor 2 satisfies a predetermined condition based on the monitoring result by the operating state monitoring unit 62, the delay time Td is made shorter than the reference value T0. Here, the above-mentioned predetermined condition as a determination criterion for determining whether or not the delay time Td can be shortened differs depending on the operation mode of the actuator 1. Hereinafter, the method of setting the delay time Td for each operation mode by the delay time setting unit 67 will be described in detail.

[0066] First, the method of setting the delay time Td when the operation mode is set to the test operation mode will be described.

[0067] When the operation mode is set to the test operation mode, the above-mentioned predetermined conditions include that the movement amount Ms of the motor 2 has reached the reference movement amount Mth. Specifically, when the operation mode is set to the test operation mode, the delay time setting unit 67 shortens the delay time Td to be shorter than the reference value T0 when it detects that the movement amount Ms of the motor 2 has reached the reference movement amount Mth. Specifically, the delay time setting unit 67 sets the delay time Td to the reference value T0 when the operation mode is set to the test operation mode, and changes the delay time Td from the reference value T0 to the lower limit value TL when it detects that the movement amount Ms of the motor 2 has reached the reference movement amount Mth. Here, the lower limit value TL is smaller than the reference value T0 (TL < T0).

[0068] For example, consider a case where, during the manufacturing or inspection stage of the actuator 1, after applying grease to the drive part (such as a gear) of the actuator 1, the motor 2 is operated by a predetermined amount to perform a process of allowing the grease to conform.

[0069] First, after the actuator 1 (motor drive control device 5) is started, in the control circuit 6, the operation mode setting unit 66 sets the operation mode to the normal operation mode, and the delay time setting unit 67 sets the delay time Td to the reference value T0 (initial value) (Td = T0). Then, a drive command signal Sc including information specifying the test operation mode as the operation mode and information specifying the target movement amount of the motor 2 (for example, 50000 steps) is input from the host device 10 or another external device to the motor drive control device 5.

[0070] The control circuit 6 starts driving the motor 2 based on the input drive command signal Sc. That is, the operation mode setting unit 66 changes the operation mode from the normal operation mode to the test operation mode and instructs each functional unit to start driving control of the motor 2. As a result, the drive control signal generation unit 69 generates drive control signals Sda and Sdb based on the zero-cross detection signal Sz and the delay time Td (= T0), and the motor 2 starts to rotate.

[0071] After the rotation of the motor 2 starts, the operation state monitoring unit 62 monitors the rotation speed Sr of the motor 2, the movement amount Ms of the motor 2, and the presence or absence of out-of-synchronization every one drive step, and appropriately stores this information in the storage unit 68. The delay time setting unit 67 determines whether or not the movement amount Ms of the motor 2 has reached the reference movement amount Mth (for example, 5000 steps). When the movement amount Ms of the motor 2 has not reached the reference movement amount Mth (for example, 5000 steps), the delay time setting unit 67 continues to set the delay time Td to the reference value T0. When the movement amount Ms of the motor 2 has reached the reference movement amount Mth (for example, 5000 steps), the delay time setting unit 67 changes the delay time Td from the reference value T0 to the lower limit value TL (Td = TL). Here, the reference movement amount Mth may be a value larger than the movement amount corresponding to the time required for the rotation of the motor 2 to become sufficiently stable after the rotation is started.

[0072] The drive control signal generation unit 69 generates drive control signals Sda and Sdb based on the zero-cross detection signal Sz and the changed delay time Td (= TL). Thereby, when the load of the motor 2 has not changed before and after the change of the delay time Td, the rotation speed Sr of the motor 2 after the change of the delay time Td becomes faster than the rotation speed Sr of the motor 2 before the change of the delay time Td. Thereafter, when the movement amount Ms of the motor 2 reaches the target movement amount, the control circuit 6 stops the rotation of the motor 2.

[0073] FIGS. 5A and 5B are diagrams showing the simulation results of the time required to move the motor 2 to the target movement amount (target rotation position) in the test operation mode.

[0074] FIG. 5A shows the waveform of the coil current of the motor 2 when the motor 2 is rotated by 4830 steps with the delay time Td fixed to the reference value T0 (= 100 μs). FIG. 5B shows the waveform of the coil current of the motor 2 when the motor 2 is rotated by 4830 steps after the delay time Td is changed from the reference value T0 (= 100 μs) to the lower limit value TL (= 0 μs) after the motor 2 is rotated by a predetermined amount.

[0075] As shown in FIG. 5A, when the delay time Td is fixed to the reference value T0 (= 100 μs) and the motor 2 is rotated by 4830 steps, the required time is 31.954 [s]. On the other hand, as shown in FIG. 5B, after the motor 2 is rotated by a predetermined amount, when the delay time Td is changed from the reference value T0 (= 100 μs) to the lower limit value TL (= 0 μs) and the motor 2 is rotated by 4830 steps, the required time becomes 29.185 [s].

[0076] Thus, in the test operation mode, by shortening the delay time Td at the commutation of the coil 4 after the motor 2 has rotated by a predetermined amount, it becomes possible to shorten the time required to rotate the motor 2 to the target movement amount.

[0077] Next, a method for setting the delay time Td when the operation mode is set to the normal operation mode will be described.

[0078] When the operation mode is set to the normal operation mode, the delay time setting unit 67 dynamically switches the delay time Td according to the rotation speed Sr of the motor 2. For example, the delay time setting unit 67 executes a process of determining the delay time Td every predetermined number of drive steps (for example, every 1 drive step).

[0079] Specifically, when the operation mode is set to the normal operation mode, when the delay time setting unit 67 detects that the operation state of the motor 2 satisfies a predetermined condition, the delay time Td at the commutation of the coil 4 is shortened. For example, when the operation mode is set to the normal operation mode and the delay time setting unit 67 detects that the operation state of the motor 2 satisfies the above-mentioned predetermined condition, the delay time Td is shortened by a unit amount Δtd from the value set at that time by executing a delay time shortening process. When the delay time Td reaches the lower limit value TL by the delay time shortening process, the delay time Td is fixed to the lower limit value TL.

[0080] Here, the above-mentioned predetermined conditions when the operation mode is set to the normal operation mode include that the rotational speed of the motor 2 is equal to or higher than the first reference rotational speed Sb1. Further, the above-mentioned predetermined conditions include that when the rotational speed Sr of the motor 2 is equal to or higher than the second reference rotational speed Sb2 and lower than the first reference rotational speed Sb1, the rotational speed Sr is increasing compared to the value obtained immediately before.

[0081] The first reference rotational speed Sb1 and the second reference rotational speed Sb2 are values that serve as references when changing the delay time Td in the normal operation mode. The first reference rotational speed Sb1 is set to a value equal to or higher than the rotational speed threshold Sth. For example, the first reference rotational speed Sb1 is a value that is α times (α is an integer equal to or greater than 1) the rotational speed threshold Sth. The second reference rotational speed Sb2 is set to a value equal to or higher than the rotational speed threshold Sth and lower than the first reference rotational speed Sb1 (Sth ≤ Sr2 < Sr1). For example, the second reference rotational speed Sb2 is a value that is β times (β is an integer smaller than α) the rotational speed threshold Sth.

[0082] More specifically, when the operation mode is set to the normal operation mode, the delay time setting unit 67 acquires the rotational speed Sr of the motor 2 calculated by the rotational speed calculation unit 64 for each drive step. When the rotational speed Sr is equal to or higher than the first reference rotational speed Sb1, the delay time setting unit 67 executes a delay time shortening process. Also, when the rotational speed Sr is equal to or higher than the second reference rotational speed Sb2 and lower than the first reference rotational speed Sb1, and the rotational speed Sr is increasing compared to the value obtained immediately before, the delay time setting unit 67 executes a delay time shortening process.

[0083] On the other hand, when the operation mode is set to the normal operation mode, if the delay time setting unit 67 detects that the operating state of the motor 2 does not satisfy the above-mentioned predetermined conditions, it increases the delay time Td or returns the delay time Td to the initial value (reference value T0). Specifically, when the rotation speed Sr is equal to or higher than the second reference rotation speed Sb2 and lower than the first reference rotation speed Sb1 and the rotation speed Sr has not increased from the value obtained immediately before, the delay time setting unit 67 executes a delay time extension process of extending the delay time Td by a unit amount Δtd from the value set at that time. Further, when the operation mode is set to the normal operation mode, the delay time setting unit 67 resets the delay time Td to the initial value (reference value T0) when the rotation speed Sr is lower than the second reference rotation speed Sb2.

[0084] Next, the flow of the process related to the method of setting the delay time Td when the operation mode is set to the normal operation mode will be described with reference to the drawings.

[0085] FIG. 6 is a flowchart showing an example of the flow of the process related to the setting of the delay time Td when the operation mode is set to the normal operation mode.

[0086] For example, after the motor drive control device 5 in the actuator 1 is started, the operation mode setting unit 66 of the control circuit 6 sets the operation mode to the normal operation mode. When information instructing the start of driving of the motor 2 and information specifying the target movement amount of the motor 2 are input to the motor drive control device 5 as a drive command signal Sc from the host device 10, the control circuit 6 starts driving the motor 2 based on the drive command signal Sc. That is, the operation mode setting unit 66 instructs each functional unit to start driving control of the motor 2. As a result, the drive control signal generation unit 69 generates drive control signals Sda and Sdb based on the zero-cross detection signal Sz and the delay time Td (= T0), and the motor 2 starts to rotate.

[0087] While the motor 2 is rotating, the operation state monitoring unit 62 monitors the rotation speed Sr of the motor 2, the movement amount Ms of the motor 2, and the presence or absence of out-of-phase for each drive step, and stores this information in the storage unit 68. The delay time setting unit 67 determines the delay time Td according to the following processing procedure every predetermined number of drive steps (here, one drive step).

[0088] As shown in FIG. 6, first, the out-of-synchronization determination unit 65 determines whether the rotational speed Sr of the motor 2 is equal to or higher than the rotational speed threshold value Sth (step S1). When the rotational speed Sr is lower than the rotational speed threshold value Sth (step S1: NO), the out-of-synchronization determination unit 65 determines that the motor 2 is out of synchronization (step S8). Thereafter, for example, the control circuit 6 stops the operation of the motor 2 and transmits an output signal So indicating that out-of-synchronization has occurred to the host device 10.

[0089] On the other hand, when the rotational speed Sr is equal to or higher than the rotational speed threshold value Sth (step S1: YES), the delay time setting unit 67 determines whether the rotational speed Sr is equal to or higher than the first reference rotational speed Sb1 (step S2). When the rotational speed Sr is equal to or higher than the first reference rotational speed Sb1 (step S2: YES), the delay time setting unit 67 executes a delay time shortening process (step S5). Specifically, the delay time setting unit 67 shortens the delay time Td by a unit amount Δtd from the value set at that time.

[0090] On the other hand, when the rotational speed Sr is lower than the first reference rotational speed Sb1 (step S2: NO), the delay time setting unit 67 determines whether the rotational speed Sr is equal to or higher than the second reference rotational speed Sb2 (step S3). When the rotational speed Sr is lower than the second reference rotational speed Sb2 (step S3: NO), the delay time setting unit 67 returns the delay time Td to the initial value (reference value T0) (step S7).

[0091] When the rotational speed Sr is equal to or higher than the second reference rotational speed Sb2 (step S3: YES), the delay time setting unit 67 determines whether the rotational speed Sr is greater than the rotational speed Sr acquired immediately before (step S4). Specifically, the delay time setting unit 67 compares the rotational speed Sr(N) acquired at the current drive step N with the rotational speed Sr(N−1) acquired at the previous drive step (N−1). When the rotational speed Sr(N) is greater than the rotational speed Sr(N−1), the delay time setting unit 67 executes a delay time shortening process (step S5). On the other hand, when the rotational speed Sr(N) is smaller than the rotational speed Sr(N−1), the delay time setting unit 67 executes a delay time extension process (step S6). Specifically, the delay time setting unit 67 extends the delay time Td by a unit amount Δtd from the value set at that time.

[0092] In this way, until the actuator 1 (motor 2) reaches the target position, the delay time setting unit 67 executes processing according to the above-described procedure for each predetermined drive step, thereby dynamically changing the delay time Td at the commutation of the coil 4 of the motor 2.

[0093] As described above, when the motor drive control device 5 according to the present embodiment generates the drive control signal Sd so as to perform commutation of the coil 4 after the elapse of the delay time Td since the zero crossing of the back electromotive voltage generated in the non-excited phase coil 4 in the motor 2 is detected, when the operating state of the motor 2 satisfies a predetermined condition, the delay time Td is made shorter than the reference value T0. According to this, since the delay time Td is dynamically changed according to the operating state of the motor 2, it is possible to increase the rotational speed of the motor 2 without impairing the stability of the operation of the motor 2.

[0094] Specifically, when the operation mode is set to the normal operation mode, the motor drive control device 5 makes the delay time Td shorter than the reference value T0 when the rotational speed Sr is equal to or higher than the first reference rotational speed Sb1. Generally, when performing drive control to commutate the coil in response to the zero crossing of the reverse voltage, the lighter the load of the motor, the faster the rotation speed of the motor, and the heavier the load, the slower the rotation speed of the motor. And when the load is light, the motor 2 can operate stably even if the delay time Td during commutation of the coil 4 is set short. Therefore, as described above, in the normal operation mode, the first reference rotation speed Sb1 is set, and when the rotation speed Sr of the motor 2 is equal to or higher than the reference rotation speed Sb1, the delay time Td is made shorter than the reference value T0. According to this, when the load of the motor 2 is light, the commutation speed increases, so it becomes possible to increase the rotation speed of the motor 2 without impairing the stability of the operation of the motor 2.

[0095] Also, when the operation mode is set to the test operation mode, the motor drive control device 5 shortens the delay time Td from the reference value T0 when the moving amount Ms of the motor 2 reaches a predetermined value (reference moving amount Mth). As described above, when performing the process of breaking in the grease applied to the drive part (such as gears) of the actuator at the manufacturing stage or inspection stage of the actuator 1, the operation mode is set to the test operation mode. When performing this process, usually, the load on the motor is in the lightest state. Therefore, as described above, in the test operation mode, the reference moving amount Mth is set, and when the moving amount Ms of the motor 2 reaches the reference moving amount Mth, the delay time Td is made shorter than the reference value T0. According to this, the delay time Td is not changed until the operation of the motor 2 becomes stable, and after the operation of the motor 2 becomes stable, the delay time Td is shortened, so it becomes possible to increase the rotation speed of the motor 2 without impairing the stability of the operation of the motor 2. Thereby, the tact time in the manufacturing stage or inspection stage of the actuator 1 can be shortened.

[0096] Also, when the operation mode of the motor drive control device 5 according to the present embodiment is set to the normal operation mode, when the rotation speed Sr is equal to or higher than the second reference rotation speed Sb2 and lower than the first reference rotation speed Sb1, and the rotation speed Sr is increasing compared to the value obtained immediately before, the delay time Td is made shorter than the reference value T0.

[0097] By setting a plurality of reference rotational speeds serving as criteria for shortening the delay time Td, it becomes possible to set a more appropriate value of the delay time Td according to the operating state of the motor 2. That is, even if the rotational speed Sr has not reached the first reference rotational speed Sb1, when the rotational speed Sr is equal to or higher than the second reference rotational speed Sb2 and the rotational speed Sr is increasing, it can be determined that sufficient torque is being generated to drive the load of the motor 2. In this case, as described above, the motor drive control device 5 shortens the delay time Td. Thereby, it becomes possible to increase the rotational speed of the motor 2 without impairing the stability of the operation of the motor 2. On the other hand, when the rotational speed Sr is equal to or higher than the second reference rotational speed Sb2 and smaller than the first reference rotational speed Sb1, and the rotational speed Sr is decreasing from the value obtained immediately before, as described above, the motor drive control device 5 makes the delay time Td longer than the reference value T0. According to this, when there is a possibility that the torque for driving the load of the motor 2 is insufficient, since the delay time Td is extended, it becomes possible to prevent a decrease in the stability of the operation of the motor 2 due to the shortage of the delay time Td.

[0098] Further, when changing the delay time Td in the normal operation mode, the motor drive control device 5 changes the delay time Td step by step in units of an amount Δtd by a delay time shortening process or a delay time extension process. According to this, it becomes possible to prevent the operation of the motor 2 from becoming unstable due to a sharp change in the delay time Td.

[0099] Further, when the rotational speed Sr is smaller than the second reference rotational speed Sb2 in the normal operation mode, the motor drive control device 5 returns the delay time Td to the reference value T0 (initial value). According to this, for example, when the load suddenly increases during the drive of the motor 2, by quickly returning the delay time Td to the initial value, it becomes possible to prevent a decrease in the stability of the operation of the motor 2 due to the shortage of the delay time Td.

[0100] In addition, in the motor drive control device 5, a rotation speed threshold value Sth smaller than the second reference rotation speed Sb2 is set, and when the rotation speed Sr is smaller than the rotation speed threshold value Sth, it is determined that the motor 2 is out of synchronization. According to this, it becomes possible to easily detect the presence or absence of the occurrence of out-of-synchronization of the motor 2.

[0101] ≪Expansion of Embodiment≫ As described above, the invention made by the present inventors has been specifically described based on the embodiments. However, needless to say, the present invention is not limited thereto, and various modifications can be made without departing from the gist thereof.

[0102] For example, in the above embodiment, the case where the process of determining the delay time Td (steps S1 to S8 in FIG. 6) is executed every one drive step in the normal operation mode has been illustrated. However, the present invention is not limited to this, and it may be executed every plurality of drive steps such as two drive steps. In this case, the acquired value of the rotation speed Sr of the motor 2 may be the average value of the rotation speeds measured during the plurality of drive steps.

[0103] In addition, the number of phases of the motor 2 in the above embodiment is not limited to two phases. The motor 2 is not limited to a stepping motor. For example, the motor 2 may be a brushless DC motor.

[0104] In addition, the above-described flowchart shows an example for explaining the operation, and is not limited thereto. That is, the steps shown in each figure of the flowchart are specific examples and are not limited to this flowchart. 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 Reference Numerals

[0105] 1... Actuator, 2... Motor (stepping motor), 3... Rotor, 3n... N pole, 3s... S pole, 4, 4a, 4b... Coil, 5... Motor drive control device, 6... Control circuit, 7... Voltage detection circuit, 8... Drive circuit, 9a, 9b... Inverter circuit, 10... Host device, 61... Zero-crossing detection unit, 62... Operating state monitoring unit, 63... Movement amount calculation unit, 64... Rotation speed calculation unit, 65... Out-of-step determination unit, 66... Operating mode setting unit, 67... Delay time setting unit, 68... Memory unit, Ms... Movement amount, Mth... Reference movement amount Mth, Sc... Drive command signal, Sd, Sda, Sdb... Drive control signal, Sr... Rotation speed, Sth... Rotation speed threshold value, Sb1... First reference rotation speed, Sb2... Second reference rotation speed, Td... Delay time, T0... Reference value, Δtd... Unit amount, TL... Lower limit value.

Claims

1. A control circuit that generates a drive control signal for controlling the drive of a motor having a multi-phase coil, A drive circuit that drives the coil based on the drive control signal, A voltage detection circuit that detects the voltage of the coil, and includes, The control circuit, A zero-cross detection unit that detects a zero-cross of a back electromotive voltage generated in the non-energized phase coil based on the voltage detected by the voltage detection circuit, A delay time setting unit that sets a delay time during commutation of the coil, A drive control signal generation unit that generates the drive control signal so as to perform commutation of the coil after the elapse of the delay time since the zero-cross is detected by the zero-cross detection unit, An operating state monitoring unit that monitors the operating state of the motor, and has, The delay time setting unit sets the delay time to a reference value, and when it is detected that the operating state satisfies a predetermined condition based on the monitoring result by the operating state monitoring unit, the delay time is made shorter than the reference value A motor drive control device.

2. In the motor drive control device according to claim 1, It further has an operation mode setting unit that sets an operation mode related to the drive of the motor, As the operation mode, it includes a normal operation mode and a test operation mode, The monitoring result by the operating state monitoring unit includes the rotational speed of the motor and the moving amount of the motor, The predetermined condition when the operation mode is set to the normal operation mode includes that the rotational speed is equal to or higher than a first reference rotational speed, The predetermined condition when the operation mode is set to the test operation mode includes that the moving amount has reached a reference moving amount A motor drive control device.

3. In the motor drive control device according to claim 2, The delay time setting unit sets the delay time to the reference value when the operation mode is set to the test operation mode, and when it is detected that the moving amount has reached the reference moving amount, the delay time is changed from the reference value to a value smaller than the reference value A motor drive control device.

4. In the motor drive control device according to claim 2, A second reference rotational speed higher than the first reference rotational speed is set, The predetermined condition when the operation mode is set to the normal operation mode includes that the rotational speed is equal to or higher than the second reference rotational speed and smaller than the first reference rotational speed, and the rotational speed is rising compared to the value obtained immediately before Motor drive control device.

5. In the motor drive control device according to claim 4, when the operation mode is set to the normal operation mode, the delay time setting unit executes a delay time shortening process of shortening the delay time by a unit amount from the value set at that time when it is detected that the operation state satisfies the predetermined condition. Motor drive control device.

6. In the motor drive control device according to claim 5, when the operation mode is set to the normal operation mode, the delay time setting unit executes a delay time extension process of extending the delay time by the unit amount from the value set at that time when the rotational speed is equal to or higher than the second reference rotational speed and lower than the first reference rotational speed and the rotational speed has not increased from the value obtained immediately before. Motor drive control device.

7. In the motor drive control device according to claim 6, when the rotational speed is lower than the second reference rotational speed, the delay time setting unit returns the delay time to the initial value. Motor drive control device.

8. In the motor drive control device according to claim 7, a threshold value lower than the second reference rotational speed is set for determining out-of-step of the motor, and when the rotational speed is lower than the threshold value, the operation state monitoring unit determines that the motor is out of step. Motor drive control device.

9. the motor, and a motor drive control device according to any one of claims 1 to 8. Actuator.

10. A motor control method for controlling the drive of a motor having a plurality of phase coils, a first step of detecting a zero cross of a back electromotive voltage generated in the non-energized phase coil, a second step of setting a delay time at the commutation of the coil, a third step of driving the motor to perform commutation of the coil after the elapse of the delay time after the zero cross is detected in the first step, and a fourth step of monitoring an operation state of the motor, wherein the second step includes a fifth step of setting the delay time to a reference value, and a sixth step of shortening the delay time from the reference value when the operation state of the motor monitored in the fourth step satisfies a predetermined condition. Motor drive control method.

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