JP6064672B2 - Motor drive device - Google Patents

Description

  The present invention relates to a motor drive device, and more particularly, to a circuit that suppresses abnormal noise at startup due to a clearance between a load connected to a rotating shaft of a motor and the rotating shaft.

Conventionally, as a motor drive device, for example, there is a fan motor drive device that drives a fan motor 4 to which a fan (not shown) shown in FIG. 5 is connected. The fan motor driving device receives a command rotational speed value designated by another device (not shown), outputs a command voltage corresponding to the command rotational speed value, and receives a command voltage, and a phase voltage corresponding to the signal. And a drive circuit 2 that inputs a rotation position signal output from the fan motor 4 and converts it into a rotation pulse signal and outputs it to the control circuit 1, and is not shown in accordance with the input drive signal. A drive circuit 3 including an intelligent power module that converts a DC power source into a three-phase phase voltage and outputs the voltage to the fan motor 4 is provided.
The control circuit 1 is composed of, for example, a microcomputer, and an applied voltage command signal (PWM signal) corresponding to the rotational speed of the fan motor 4 in order to perform feedback control so that the fan motor 4 has the commanded rotational speed value indicated. And a D / A converter 5 that converts the input applied voltage command signal into a DC voltage and outputs it as a command voltage.

  The D / A converter 5 includes an integrating circuit composed of a resistor 5a and a capacitor 5b, and outputs a DC voltage corresponding to the applied voltage command signal by integrating the applied voltage command signal. To do. In this integrating circuit, an applied voltage command signal is input to one end of the resistor 5a, and a command voltage is output from the other end. One end of the capacitor 5b is connected to the other end of the resistor 5a, and the other end of the capacitor 5b is connected to the ground. The time constant of the integrating circuit is determined by the capacitor 5b and the resistor 5a. In addition, a resistor 5c is provided in parallel with the capacitor 5b, and the command voltage is divided by the resistor 5a and the resistor 5c.

The control unit 1a outputs an applied voltage command signal when the fan motor 4 is rotated. The controller 1a gradually increases the duty of the pulse of the applied voltage command signal in order to gradually increase the rotational speed. For this reason, the D / A converter 5 to which this applied voltage command signal is input integrates this signal, and as a result, the command voltage gradually increases.
The control unit 1a stores the increase in the rotation speed value for instructing the rotation speed at the time of activation as a rotation speed table, and the time elapses during the transition from the start of the fan motor 4 to the command rotation speed. Corresponding to the rotation speed table, the rotation speed value is read out, the read rotation speed value is converted into a PWM duty value, and an applied voltage command signal is generated and output.

  The drive circuit 2 to which the command voltage is input outputs an inverter-controlled drive signal to the drive circuit 3 in order to apply a phase voltage to the fan motor 4 in response to this signal, and the drive circuit 3 A three-phase motor applied voltage is output to the fan motor 4 in response to the signal.

  As a result, the fan motor 4 rotates while gradually increasing the rotation speed, and a rotation speed pulse signal composed of pulses at time intervals corresponding to the rotation speed is output from the drive circuit 2 to the control circuit 1. In the control circuit 1, the difference between the instructed command rotational speed and the current rotational speed is calculated, and the applied voltage command signal is feedback-controlled so that they are equal.

By the way, when such a circuit is applied to a fan motor drive device for an outdoor unit of a large air conditioner, the following problems occur because the mass of the driven fan is large.
FIG. 6 is a cross-sectional view of a main part near the center of a fan 90 (propeller fan) attached to the fan motor 4, and shows a cross section perpendicular to the direction of the rotation axis 93 of the fan motor 4.

  As shown in FIG. 6A, the rotation center of the fan motor 4 is provided with a columnar fan base 91 having a plurality of blades on the outer periphery, and a rotating shaft 93 is inserted on the inner periphery thereof. A boss 92 is provided. A part of the outer periphery of the rotating shaft 93 is cut into a flat surface and the cross section is formed in a D shape. The space inside the boss 92 is also formed in a D shape corresponding to this shape. A clearance 94 is provided between the rotary shaft 93 and the inner surface of the boss 92 in order to improve workability.

  As shown in FIG. 6B, when the rotating shaft 93 starts to rotate clockwise, the clearance 94 causes the sliding of the rotating shaft 93 that has started rotating with respect to the boss 92, and the angle 95 of the rotating shaft 93 changes to the boss. Contacting the inner surface of 92, a shocking sound is generated. Depending on the size of the clearance 94 and the momentum with which the rotary shaft 93 contacts, this impact sound is heard as an irritating noise every time the fan motor 4 is started. Of course, there are mechanical measures such as tightening with a fixing screw (not shown) or adding a cushioning material such as rubber, but there are problems of durability and an increase in cost.

  As described above, Patent Document 1 discloses that noise generated in the initial stage of rotation is reduced. In Patent Document 1, regarding a stepping motor and a gear serving as a load, when the gear backlash period (light load) elapses at the start of motor rotation, the gear that becomes a high load is rotated. When the stepping motor is started with the corresponding voltage, the backlash period of the gear at the start of motor rotation is set to a low voltage to solve the problem of abnormal noise due to gear meshing when shifting from light load to high load. An abnormal noise is suppressed by driving at a normal voltage when driving and rotating a gear that becomes a high load (see, for example, Patent Document 1).

  As described above, since the applied voltage command signal is output from the control unit 1a by software in the motor drive device of FIG. 5, the applied voltage command signal at the start of rotation is simply changed by changing the rotation speed table instructing an increase in rotation speed. Can be temporarily controlled.

  However, when dealing with software, in general, the software is often masked in the ROM in the microcomputer, and cannot be easily changed later. In addition, when it is supported by software, there is a problem in that it requires re-tuning, evaluation, and confirmation of the rotation speed table every time a new product is developed, resulting in a development man-hour.

Japanese Patent Laid-Open No. 4-261597 (page 3, FIG. 1)

  The present invention solves the above-described problems and eliminates the need for software work for each device for abnormal noise at the time of motor startup that occurs between the rotating shaft of the motor and a load attached thereto. Is realized by a simple electronic circuit.

In order to solve the above-mentioned problems, the present invention according to claim 1 of the present invention is a motor driving device for driving a motor in accordance with an inputted command rotational speed value, and indicates the rotational speed of the motor. By gradually increasing the command voltage signal and outputting it, the rotation speed of the motor is controlled to become the command rotation speed value, and a rotation pulse signal corresponding to the rotation position signal output by the motor is input. A control circuit;
A drive circuit that outputs a drive signal so as to achieve the rotational speed of the motor indicated by the input command voltage signal, and a driving phase voltage corresponding to the input drive signal is output to the motor A drive circuit, a rotation speed determination circuit that outputs a result of comparing the rotation speed based on the input rotation pulse signal and a predetermined rotation speed as a rotation speed determination result signal, and the rotation speed determination result signal are input. And command voltage lowering means for dividing and lowering the voltage of the command voltage until the rotation speed by the rotation pulse signal becomes equal to or higher than the predetermined rotation speed.

According to a second aspect of the present invention, there is provided a motor driving device for driving a motor in accordance with an inputted command rotational speed value, wherein a command voltage signal for instructing the motor rotational speed is gradually increased. A control circuit for controlling the rotational speed of the motor to be the command rotational speed value by outputting and a rotational pulse signal corresponding to the rotational position signal output by the motor;
A drive circuit that outputs a drive signal so as to achieve the rotational speed of the motor indicated by the input command voltage signal, and a driving phase voltage corresponding to the input drive signal is output to the motor A drive circuit, a rotational speed determination circuit that outputs a result of comparing the rotational speed of the input rotational position signal and a predetermined rotational speed as a rotational speed determination result signal, and the rotational position signal, A rotation direction detection circuit that outputs forward / reverse rotation, which is a detection result of the rotation direction of the motor, as a rotation direction signal, the rotation direction signal and the rotation speed determination result signal are input, and the rotation speed based on the rotation position signal Command voltage lowering means for dividing and lowering the voltage of the command voltage until the motor reaches the predetermined rotation speed and until the motor is rotated in the forward direction. The features.

  By using the above means, according to the motor driving device of the present invention, the command voltage is reduced when the motor is less than the predetermined rotational speed, so compared to when the command voltage is not reduced at the beginning of driving of the motor, The rotating shaft of the motor can be gently pressed against the load, and abnormal noise generated by the clearance between the load and the rotating shaft of the motor can be reduced.

  Moreover, since it is a response | compatibility by an electrical circuit, the corresponding | compatible operation | work for every apparatus by software becomes unnecessary for a rotation speed fall.

It is a block diagram which shows Example 1 of the motor drive device by this invention. It is a block diagram which shows Example 2 of the motor drive device by this invention. It is explanatory drawing explaining operation | movement of the motor drive device of Example 1. FIG. It is explanatory drawing explaining operation | movement of the motor drive device of Example 2. FIG. It is a block diagram which shows the conventional motor drive device. It is a principal part sectional drawing of the fan used conventionally and in a present Example.

  DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail as examples based on the attached drawings.

FIG. 1 is a block diagram showing an embodiment of a fan motor driving apparatus that drives a fan motor 4 to which a fan (not shown) is connected according to an instruction from the control circuit 1.
The fan motor driving device receives a command rotational speed value designated by another device (not shown), outputs a command voltage corresponding to the command rotational speed value, and receives a command voltage, and a phase voltage corresponding to the signal. And a drive circuit 2 that inputs a rotation position signal output from the fan motor 4 and converts it into a rotation pulse signal and outputs it to the control circuit 1, and is not shown in accordance with the input drive signal. A drive circuit 3 including an intelligent power module that converts a DC power source into a three-phase phase voltage and outputs the voltage to the fan motor 4 is provided.
The control circuit 1 is composed of, for example, a microcomputer, and an applied voltage command signal (PWM signal) corresponding to the rotational speed of the fan motor 4 in order to perform feedback control so that the fan motor 4 has the commanded rotational speed value indicated. And a D / A converter 5 that converts the input applied voltage command signal into a DC voltage and outputs it as a command voltage.
Further, the fan motor driving device includes a rotation speed determination circuit 6 that outputs a rotation speed determination result signal composed of a comparison result between the rotation speed obtained from the input rotation pulse signal and a predetermined rotation speed value, and a D / A converter. 5 is provided with a resistor 8 having one end connected to the output 5 and a switch 7 for switching a short circuit / opening between the other end of the resistor 8 and the ground according to the state of the rotational speed determination result signal. The resistor 8 and the switch 7 constitute a command voltage lowering unit 20.

The D / A converter 5 includes an integrating circuit composed of a resistor 5a and a capacitor 5b, and outputs a DC voltage corresponding to the applied voltage command signal by integrating the applied voltage command signal. To do. In this integrating circuit, an applied voltage command signal is input to one end of the resistor 5a, and a command voltage is output from the other end. One end of the capacitor 5b is connected to the other end of the resistor 5a, and the other end of the capacitor 5b is connected to the ground. The time constant of the integrating circuit is determined by the capacitor 5b and the resistor 5a. In addition, a resistor 5c is provided in parallel with the capacitor 5b, and the command voltage is divided by the resistor 5a and the resistor 5c.
On the other hand, since the command voltage is divided by the resistor 5a, the resistor 8, and the resistor 5c, when the switch 7 is turned on (short circuit), compared to when the switch 7 is turned off (open). The command voltage decreases. Since the resistor 8 is set to be very small as compared with the resistor 5c, the voltage is almost divided between the resistor 5a and the resistor 8.

  The rotation speed determination circuit 6 has a rotation speed threshold value, which is a voltage value corresponding to a predetermined rotation speed, in the rotation speed determination circuit 6, and an integrated voltage obtained by integrating the rotation speed threshold value and the input rotation pulse signal. Is output as a result of comparison with the rotation speed determination result. In this embodiment, at least when the fan motor 4 is 60 revolutions / minute (one revolution / second) or more, the rotational speed determination result signal changes from the low level to the high level.

The control unit 1a outputs an applied voltage command signal when the fan motor 4 is rotated. The controller 1a gradually increases the pulse duty of the applied voltage command signal in order to gradually increase the rotational speed. For this reason, the D / A converter 5 to which this applied voltage command signal is input integrates this signal, and as a result, the command voltage gradually increases.
Note that the control unit 1a stores an increase in the numerical value for instructing the rotational speed at the time of startup as a rotational speed table, and the time elapses while the fan motor 4 starts to start moving to the commanded rotational speed. Correspondingly, the rotation speed value is read from the rotation speed table, and the read rotation speed value is converted into a PWM duty value to generate and output an applied voltage command signal.
On the other hand, when the command voltage is gradually increased, the fan motor 4 starts to rotate and generates a rotation pulse signal. The switch 7 remains on until the rotation speed determination result signal from the rotation speed determination circuit 6 becomes high level. Therefore, the command voltage is divided to a lower voltage than when the switch 7 is off.

  The drive circuit 2 to which this command voltage is inputted outputs a drive signal to the drive circuit 3 (intelligent power module) in order to apply a phase voltage to the fan motor 4 in response to this signal. A three-phase motor applied voltage is output to the fan motor 4 in response to the drive signal.

  As a result, the fan motor 4 rotates while gradually increasing its rotational speed, and a rotational speed pulse signal composed of pulses at time intervals corresponding to this rotational speed is output from the drive circuit 2 to the control circuit 1. In the control circuit 1, the difference between the command rotational speed instructed from a device (not shown) and the current rotational speed is calculated, and the applied voltage command signal is feedback-controlled so that they are equal.

  When the number of pulses of the rotation pulse signal increases, that is, when the rotation speed increases, the integrated voltage in the rotation speed determination circuit 6 increases, and when the voltage corresponding to a predetermined rotation speed (rotation speed threshold) is reached, the rotation speed determination result. The signal changes from low level to high level, the switch 7 is turned off, and the command voltage increases. Thus, until the rotational speed reaches the predetermined rotational speed, the command voltage is divided and the fan motor 4 rotates at a lower voltage than when the switch 7 is OFF. Weld gently. For this reason, abnormal noise is suppressed and the number of revolutions is quickly increased thereafter.

FIG. 3 is an explanatory diagram for explaining the operation of the fan motor driving apparatus according to the first embodiment.
3, the horizontal axis represents time, and FIG. 3 (1) applied voltage command signal, FIG. 3 (2) command voltage, FIG. 3 (3) rotation pulse signal, and FIG. 3 (4) rotation speed determination result signal in the vertical direction. Respectively.

  FIG. 3A shows an applied voltage command signal (PWM signal) output from the control unit 1a. The controller 1a controls the duty of the applied voltage command signal so as to gradually increase in order to gradually increase the rotational speed of the fan motor 4.

  On the other hand, no voltage is applied to the fan motor 4 during the period when the controller 1a does not output the applied voltage command signal, and the rotating shaft does not rotate. Therefore, the rotation pulse signal is not output, and the integrated voltage in the rotation speed determination circuit 6 becomes substantially zero volts in the period T1, as shown in FIG. 3 (4). As a result, since the integrated voltage is equal to or lower than the rotation speed threshold voltage, the rotation speed determination result signal is at a low level, and as a result, the switch 7 is also turned on (short circuit).

  When the applied voltage command signal gradually increases (duty increases), the fan motor 4 starts rotating. As a result, as shown in FIG. 3 (3), the rotation pulse signal is sequentially generated in the first and second pulses. . Since the rotation pulse signal of this embodiment is generated once for each rotation of the fan motor 4, when the second pulse is generated, the fan motor 4 has made at least one rotation. The boss is in pressure contact. For this reason, the rotational speed determination circuit 6 uses the integral voltage corresponding to the rotational pulse signal as the voltage of the rotational speed threshold (predetermined rotational speed value to 60 revolutions / min). A rotational speed threshold value at which the rotating shaft of the fan motor 4 and the fan boss are surely pressed against each other is experimentally obtained in advance.

  As shown in FIG. 3 (4), when the rotation speed by the rotation pulse signal becomes a predetermined rotation speed value to 60 rotations / min or more, the rotation speed determination result signal becomes high level. As a result, the switch 7 is turned off, the resistor 8 is electrically floating from the ground, and the command voltage division by the resistors 5a and 8 is released. For this reason, as shown in FIG. 3 (2), the command voltage rises rapidly from this point, and gradually approaches the voltage rise curve when the switch 7 is OFF.

  As described above, since the command voltage is decreased until the fan motor 4 starts rotating and reaches a predetermined rotation speed (rotation speed threshold), it is compared with the case where the command voltage is not decreased at the beginning of driving of the fan motor 4. Thus, the rotating shaft of the fan motor 4 can be gently pressed against the inner surface of the boss, and noise generated by the clearance between the fan and the rotating shaft of the fan motor 4 can be reduced.

Moreover, since it is a response | compatibility by an electrical circuit, the corresponding | compatible operation | work of the various types of apparatus by the software in the control part 1a becomes unnecessary for the rotation speed fall.
Furthermore, in order to detect the actual rotational speed via the rotational speed determination circuit 11 and reduce the command voltage correspondingly, the command voltage is set corresponding to the change in the rotational speed characteristics at the start of the rotation of the fan motor 4. The time from the start of rotation to the command rotational speed can be made shorter than when the time to decrease is fixed time with a margin. The rotation characteristic change at the start of rotation is the time from when the command voltage is output until the fan motor 4 actually reaches a predetermined rotation speed. Generally, the rotation of the fan motor 4 is caused by secular change. This time becomes longer due to an increase in load due to wear of the parts.

FIG. 2 is a block diagram showing another embodiment according to the present invention. Here, differences from the first embodiment will be described in detail.
In FIG. 2, the control unit 1a, the D / A converter 5, the drive circuit 2, the drive circuit 3, the resistor 8 and the switch 7 are the same as those in the first embodiment, and thus detailed description thereof is omitted. The rotation speed determination circuit 11, the AND circuit 10, the rotation direction detection circuit 9, and the command voltage lowering means 30 are characteristic circuits in this embodiment. The AND circuit 10, the resistor 8, and the switch 7 constitute a command voltage lowering means 30.

  The rotational speed determination circuit 11 has the same function as that of the rotational speed determination circuit 6 of the first embodiment, but one of the three rotational position signals output from the fan motor 4 is input instead of the rotational speed pulse signal. One pulse is output by rotation. Therefore, the rotation speed determination circuit 11 determines that the fan motor 4 has made at least one rotation when two pulses are detected from the rotation position signal. In this case as well, the integrated voltage obtained by integrating the rotational position signal and the voltage of the rotational speed threshold (predetermined rotational speed value to 60 revolutions / min) are compared with the rotational speed determination circuit 6 of the first embodiment. Then, a rotation speed determination result signal, which is the comparison result, is output to the AND circuit 10.

On the other hand, the rotational direction detection circuit 9 receives three rotational position signals output from the fan motor 4. The rotation position signal is a signal that can detect the rotation position finely in one rotation. In this embodiment, the fan motor 4 is provided with one rotation sensor for each angle obtained by dividing one rotation into three, and the rotation axis is When it rotates, a pulse is generated from the sensor corresponding to the rotational position. For this reason, it is possible to detect the rotation direction of forward rotation / reverse rotation by confirming the presence of the pulse of the other two rotation sensors after the pulse generated by a certain rotation sensor.
Thus, the rotation direction detection circuit 9 determines whether the fan motor 4 is rotating in the forward / reverse rotation direction, and outputs the result to the AND circuit 10 as a rotation direction signal. When the fan motor 4 is rotating forward, the rotation direction signal is at a high level. The output of the AND circuit 10 is output as a control signal for the switch 7. That is, the switch 7 is turned off when the fan motor 4 rotates at least once and is forwardly rotated.

FIG. 4 is an explanatory diagram for explaining the operation of the motor drive apparatus according to the second embodiment.
4, the horizontal axis represents time, and FIG. 4 (1) applied voltage command signal, FIG. 4 (2) command voltage, FIG. 4 (3) rotational position signal, and FIG. 4 (4) rotational speed determination result signal in the vertical direction. 4 (5) shows the rotation direction signal, and FIG. 4 (6) shows the output signal of the AND circuit 10.

  FIG. 4A shows an applied voltage command signal (PWM signal) output from the control unit 1a. The controller 1a controls the duty of the applied voltage command signal so as to gradually increase in order to gradually increase the rotational speed of the fan motor 4.

  On the other hand, during the period in which the controller 1a does not output the applied voltage command signal, no voltage is applied to the fan motor 4, and therefore the rotating shaft does not rotate. Therefore, the rotating position signal is not output. Although the voltage should be almost zero volts, the fan motor 4 is rotated in reverse by the wind blown on the fan. As a result, the integrated voltage in the rotation speed determination circuit 11 is rotated during the period T1 shown in FIG. The speed threshold may be exceeded. For this reason, the rotation speed determination result signal output from the rotation speed determination circuit 11 is at a high level.

  If this signal is used for controlling the switch 7 as it is, the switch 7 is turned off (opened) in this state, and low-speed rotation at the time of starting cannot be performed. In this embodiment, as shown in FIG. 4 (5), the AND circuit 10 performs a logical operation on the coincidence of the rotation direction signal and the rotation speed determination result signal in FIG. 4 (4), as shown in FIG. 4 (6). The switch 7 is turned off only when these signals are both at a high level. Therefore, the divided voltage of the command voltage is released from this point and the voltage starts to rise. Since the applied voltage command signal starts to be output when the fan motor 4 rotates in the reverse direction, an abnormal noise is generated at this point due to the clearance between the fan boss and the rotating shaft, but the switch 7 is turned on (short-circuited). Since the command voltage is divided and becomes a relatively low voltage, the size of the abnormal noise can be reduced as compared with the case where the command voltage is not divided.

  On the other hand, as shown in FIG. 4A, the control unit 1a gradually increases the applied voltage command signal (increases the duty) regardless of the rotation direction of the fan motor 4. Then, the fan motor 4 gradually decreases in rotational speed from the reverse rotation and eventually starts to rotate in the normal rotation direction. As a result, as shown in FIG. 4 (3), the pulse interval of the rotational position signal gradually increases, and after the rotational position signal is no longer generated, the rotational position signal is sequentially generated again in the first and second pulses.

  As described above, the rotation position signal of this embodiment is generated by one pulse every time the fan motor 4 makes one rotation. Therefore, when the second pulse is generated, the fan motor 4 has made at least one rotation. The shaft and the fan boss are in pressure contact with each other in the forward rotation direction. For this reason, the rotational speed determination circuit 11 uses the integrated voltage corresponding to the rotational position signal that is at least two pulses or more as the rotational speed threshold voltage. A rotational speed threshold value at which the rotating shaft of the fan motor 4 and the fan boss are surely pressed against each other is experimentally obtained in advance.

  As shown in FIG. 4 (4), when the rotational speed based on the rotational position signal is 60 revolutions / minute or more, the rotational speed determination result signal becomes high level, and when the rotational direction signal is high level, FIG. As shown, the output of the AND circuit 10 changes from low level to high level. As a result, the switch 7 is turned on (short-circuited) to off (opened), the resistor 8 is electrically floated from the ground, and the command voltage divided by the resistors 5a and 8 is released. For this reason, as shown in FIG. 4 (2), the command voltage rises rapidly from this point, and gradually approaches the voltage rise curve when the switch 7 is OFF.

  As described above, in addition to the effects of the first embodiment, in this embodiment, even when the fan motor 4 starts the forward rotation operation during the reverse rotation, the command voltage is divided and relatively low. Since it is a voltage, the size of abnormal noise can be reduced as compared with the case where voltage is not divided.

In the first and second embodiments, an integration circuit is used as the D / A converter 5. However, the present invention is not limited to this, and a general-purpose integrated circuit is used, or a command voltage is directly driven from the control unit 1a. You may make it output to the circuit 2. FIG. The switch 7 may be a transistor or a relay.
In the second embodiment, the rotational position signal is used as an input signal to the rotational speed determination circuit 11, but the present invention is not limited to this, and a rotational pulse signal may be used.

DESCRIPTION OF SYMBOLS 1 Control part 2 Drive circuit 3 Drive circuit 4 Fan motor
DESCRIPTION OF SYMBOLS 5 D / A converter 5a Resistance 5b Capacitor 5c Resistance 6 Rotation speed judgment circuit 7 Switch 8 Resistance 9 Rotation direction detection circuit 10 AND circuit 11 Rotation speed judgment circuit 20 Command voltage reduction means 30 Command voltage reduction means

Claims (2)

A motor driving device for driving a motor according to an inputted command rotational speed value, wherein a command voltage signal for instructing the motor rotational speed is gradually increased to output the motor rotational speed by the command rotational speed. And a control circuit that receives a rotation pulse signal corresponding to the rotation position signal output from the motor,
A drive circuit that outputs a drive signal so as to achieve the rotational speed of the motor indicated by the input command voltage signal, and a driving phase voltage corresponding to the input drive signal is output to the motor A drive circuit, a rotation speed determination circuit that outputs a result of comparing the rotation speed based on the input rotation pulse signal and a predetermined rotation speed as a rotation speed determination result signal, and the rotation speed determination result signal are input. And a command voltage reducing means for dividing and reducing the voltage of the command voltage signal until the rotation speed by the rotation pulse signal becomes equal to or higher than the predetermined rotation speed. A motor driving device for driving a motor according to an inputted command rotational speed value, wherein a command voltage signal for instructing the motor rotational speed is gradually increased to output the motor rotational speed by the command rotational speed. And a control circuit that receives a rotation pulse signal corresponding to the rotation position signal output from the motor,
A drive circuit that outputs a drive signal so as to achieve the rotational speed of the motor indicated by the input command voltage signal, and a driving phase voltage corresponding to the input drive signal is output to the motor A drive circuit, a rotational speed determination circuit that outputs a result of comparing the rotational speed of the input rotational position signal and a predetermined rotational speed as a rotational speed determination result signal, and the rotational position signal, A rotation direction detection circuit that outputs forward / reverse rotation, which is a detection result of the rotation direction of the motor, as a rotation direction signal, the rotation direction signal and the rotation speed determination result signal are input, and the rotation speed based on the rotation position signal Command voltage lowering means for dividing and lowering the voltage of the command voltage signal until the motor is at a predetermined rotational speed or higher and until the motor is rotated forward. Motor drive device, characterized in that.

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