JP2002345284A - Direct-current brushless motor and control method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce overheating and energy loss in a switching element in a direct-current brusbless motor. SOLUTION: Based on the time of rotation Tbrpm in the previous time of rotation of a rotor and a duty ratio inputted to a control portion, the on- times Ton of driving signals GU<-> , GV<-> , and GW<-> outputted to a negative pole- side transistor are set to values in synchronization with the number of rotations of the rotor.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a DC brushless motor, and is particularly effective when applied to a motor having an inverter unit including a plurality of switching elements.

[0002]

2. Description of the Related Art DC brushless motors are used in audio equipment and office automation equipment because of their high reliability and long life.
It is widely used from consumer equipment such as equipment to industrial equipment such as robots and machine tools, and will continue to be used in various fields such as automotive parts such as fan motors and power sources for electric vehicles. Conceivable.

Such a DC brushless motor is, for example, in the case of a three-phase two-pole motor, a stator in which a coil assembly formed by three coils connected in a star shape is fixed, and a permanent magnet having two magnetic poles. And a rotor to which a magnet is attached.

In the vicinity of the rotation trajectory of the rotor, there are provided position detecting means such as Hall elements arranged at regular intervals in the direction of rotation, and the rotational position of the rotor is detected by these position detecting means. It has become. Then, based on the on / off timing of the detection signal, 3
By sequentially switching the energization state of two of the coils, that is, by repeating commutation, the coil and the permanent magnet are attracted and repelled in the rotational direction to generate a rotational force on the rotor. .

As means for switching the energization state of the coil, for example, in the case of a three-phase two-pole type, a switching element pair having a positive-side switching element and a negative-side switching element is provided for three phases. A switching circuit in which each switching element pair is arranged in parallel is used. Further, the switching elements of each phase are connected to the non-connection ends of the corresponding coils, respectively, so that a so-called three-phase inverter circuit is formed as a whole. As these switching elements, semiconductor elements such as transistors and FETs that can be turned on / off by a drive signal are used.

A control unit is connected to these switching elements. The control unit performs one switching operation in order to commutate current to each coil in a predetermined order and rotate the rotor in a predetermined direction. Based on a detection signal from the above-described position detection means, a predetermined switching element is connected to the positive side transistor of the element pair and the negative side transistor of another switching element pair in the predetermined order so as to be turned on. A drive signal is output to the device.

Therefore, this DC brushless motor is controlled by the drive signal output from the control unit.

As a control method of this DC brushless motor, a so-called PWM (in which one of two switching elements corresponding to two coils to which a voltage is applied and the other switching element corresponding to a continuous ON state and the other is an intermittent ON state) is used. Pu
lse Width Modulation) control.
In this PWM control, a drive signal output from the control unit to a switching element that is turned on and off is represented by:
For example, the pulse has a predetermined carrier frequency of about 1 kHz to 10 kHz, and a predetermined duty ratio is set by changing the pulse width. Therefore, a voltage is always applied to the coil assembly of the DC brushless motor controlled by the PWM control.

[0009]

However, in the PWM control, the switching element continuously repeats a switching operation from on to off or from off to on in accordance with the carrier frequency while the pulse is being output. Become. At this time, switching elements such as transistors and FETs generate switching loss and generate heat.

Therefore, the switching element which is turned on and off by performing the PWM control generates a large amount of heat because of a large number of switching operations, resulting in overheating of the switching element and an increase in energy loss.

An object of the present invention is to reduce overheating and energy loss of a switching element of a DC brushless motor.

[0012]

A DC brushless motor according to the present invention is a DC brushless motor including a stator having a coil assembly formed by coils of a plurality of phases and a rotating body having permanent magnets. Position detecting means for detecting the position of the rotating body, rotational speed detecting means for detecting the rotating speed of the rotating body based on the position detected by the position detecting means, the on time of the drive signal of the switching element of the inverter unit, Control means for controlling in synchronization with the rotation speed of the rotating body.

In the DC brushless motor according to the present invention, energization of the coil assembly is repeated by the drive signal.

[0014] The DC brushless motor according to the present invention is characterized in that the on-time is calculated from the number of rotations of the rotating body during the previous rotation and a duty ratio input to the control means.

According to the DC brushless motor control method of the present invention, a stator having a coil assembly formed by coils of a plurality of phases, a rotating body having a permanent magnet, and position detecting means for detecting the position of the rotating body are provided. A rotational speed detecting means for detecting the rotational speed of the rotating body based on the position detected by the position detecting means, a positive switching element connected to a positive terminal of the power supply and a negative switching element connected to a negative terminal; A DC brushless motor having an inverter unit, comprising: detecting a rotation speed of the rotating body during a previous rotation, and calculating an ON time of a drive signal from the rotation speed and a predetermined duty ratio. Outputting the drive signal to at least one of the positive-side switching element and the negative-side switching element. And butterflies.

The control method of a DC brushless motor according to the present invention is characterized in that a start control for operating the rotating body from a stop state to a start determination rotation speed is performed.

In the present invention, the ON time of the drive signal for driving the switching element of the inverter unit is synchronized with the rotation speed of the rotating body, so that the number of switching operations of the switching element when performing control is performed. Therefore, overheating and energy loss of the switching element of the DC brushless motor can be reduced.

[0018]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is an explanatory view schematically showing the configuration of a DC brushless motor according to an embodiment of the present invention.

The DC brushless motor shown in FIG.
This is a three-phase two-pole type having three coils LU, LV, LW of three phases, V phase and W phase, and a permanent magnet 1 having two magnetic poles.

The motor body 2 of this DC brushless motor
Has three stators LU, LV, LV, U, V, and W for a U-phase, a V-phase, and a W-phase, which are arranged at 120 ° intervals in the rotation direction.
LW is attached. These coils LU, L
One end of each of V and LW is star-connected to each other to form a coil assembly 3.

The motor body 2 has a rotor 4 as a rotating body rotatably provided about a rotating shaft 4a. The rotor 4 rotates its magnetic poles by 180 ° in the direction of rotation. It is configured to include a permanent magnet 1 attached out of phase.

Further, in the vicinity of the rotation orbit of the rotor 4,
U as a position detecting means for detecting the position of the rotor 4
Hall elements HU, HV, HW for three phases, V phase and W phase
Are provided, and these Hall elements HU, HV, H
W is arranged at intervals of 120 ° in the rotation direction. Each Hall element HU, HV, HW is
It reacts to the magnetic flux of the permanent magnet 1 in the range of 180 degrees in mechanical angle around the position, the U-phase Hall element HU outputs the position detection signal PU, and the V-phase Hall element HV outputs the position detection signal. PV and the W-phase Hall element HW output a position detection signal PW. These position detection signals PU, PV, and PW are input to a control unit 5 as control means, and the control unit 5 generates a timing based on these position detection signals PU, PV, and PW. The drive signal is output to the switching circuit 6 in a predetermined output pattern.

The switching circuit 6 includes three positive side transistors as positive side switching elements connected to the positive terminal 7a of the DC power source 7 and negative side switching elements respectively connected to the negative terminal 7b of the DC power source 7. And three negative side transistors. These transistors are a U-phase positive-side transistor TU + and a U-phase negative-side transistor TU-, a V-phase positive-side transistor TV +, a V-phase negative-side transistor TV-, and a W-phase By connecting the positive-side transistor TW + and the negative-side transistor TW- for the W-phase to each other, three series circuits for the U-phase, V-phase, and W-phase as switching element pairs corresponding in number to the number of coils. SU, SV, and SW are formed. These series circuits SU, SV, SW are connected in parallel with each other, and this switching circuit 6 is a so-called 3
It is a phase voltage type inverter circuit. A diode D is attached between the collector and the emitter of each of these transistors, and a delay current component in the case of an inductive load is returned to a DC power supply so that no back electromotive force is applied between the collector and the emitter. Has become. In addition,
Although a transistor is used as a switching element in the present embodiment, the present invention is not limited to this, and another semiconductor element such as an FET may be used.

Each of the series circuits SU, SV, and SW has a positive-polarity and negative-polarity transistor, that is, an interconnection between the positive-polarity and negative-polarity transistors, which is connected to the non-connection end of the corresponding phase coil. I have. That is, the non-connection end of the coil LU is connected to the interconnection between the positive-side transistor TU + and the negative-side transistor TU-, and the coil L is connected to the interconnection between the positive-side transistor TV + and the negative-side transistor TV-.
The non-connection end of V is connected to the non-connection end of the coil LW at the interconnection between the positive transistor TW + and the negative transistor TW-.

The control of the DC brushless motor having such a structure is performed by a drive signal outputted from the control unit 5 to each transistor constituting the switching circuit 6. This drive signal has a rectangular waveform having an on-time for turning on the transistor, and the above-described position detection signals PU, PV, P
It is output to a predetermined transistor at a predetermined timing according to an output pattern based on W.
In this output pattern, the positive-side transistor of one DC circuit and the negative-side transistor of another DC circuit are respectively combined in a predetermined order and turned on, whereby the respective coils LU, LV, L
Current is commutated to W in a predetermined order, and the rotor 4 rotates.

FIG. 2 is a flowchart for explaining control of the DC brushless motor shown in FIG. FIG. 3 is a time chart showing an output pattern at the time of start control of the DC brushless motor shown in FIG. 1, and FIG. 4 is a time chart showing an output pattern at the time of inertia control of the DC brushless motor shown in FIG. FIG.

Next, control of the DC brushless motor will be described. The following control shows the control in the case where the stopped rotor 4 is rotated at a rotation speed at which the duty ratio becomes 50%. In the present embodiment, the control in the case where the rotor 4 is rotated at the rotation speed at which the duty ratio becomes 50% is shown. However, the present invention is not limited to this. Can be applied.

As shown in FIG. 2, first, when the DC brushless motor is stopped, that is, the rotor 4 is not rotating, and a switch (not shown) is turned on in step S1, the control unit 5 starts the control in step S2. Will start. At this time, in step S1, the control unit 5 has input that the predetermined duty ratio, that is, the duty ratio in the present embodiment is 50%. The relationship between the duty ratio and the rotation speed of the rotor 4 is confirmed in advance by experiments or the like and stored in the memory of the control unit 5. Therefore, the rotation speed of the rotor 4 when the duty ratio is 50% is also controlled. It is stored in the memory of the unit 5.

This startup control is performed to operate the rotor 4 from the stopped state to the rotation speed for starting determination. In the present embodiment, the rotation speed for starting determination is determined when the duty ratio is 50%. The rotation speed of the rotor 4 is used.

In the start control, the control unit 5 outputs a drive signal to a predetermined transistor in accordance with an output pattern for start control stored in advance in the memory shown in FIG.

FIG. 3 shows each of the Hall elements HU, H
Output waveforms of position detection signals PU, PV, PW from V, HW, output patterns of drive signals output to respective transistors based on these position detection signals PU, PV, PW, and energization by these drive signals The relationship between the energized state of each of the coils LU, LV, and LW in the state and the energized state of the coil assembly is shown, and the section indicated by the broken line is 60 ° in the mechanical angle in the rotation direction of the rotor 4. I have.

The output pattern for starting control drives this DC brushless motor at a duty ratio of 100%. For example, in section A shown in FIG. 3, drive signals GU + and GW- are output to transistors TU + and TW-. Therefore, in this section A, the current from the DC power supply 7 flows through the transistor TU +, the coil LU, the coil LW, and the transistor TW-, and the rotor 4 is connected to the coil LU and the coil LW.
W causes suction or repulsion to rotate.

Next, when the position detection signal PW is output from the Hall element HW by the rotation of the rotor 4, the output pattern for starting control has the waveform shown in the section B. In this case, drive signals GV + and GW- are output to the transistor TV + and the transistor TW- so that the current from the DC power supply 7 flows through the transistor TV +, the coil LV, the coil LW, and the transistor TW-. I have to. Therefore, the rotor 4 rotates by being attracted or repelled by the coil LV and the coil LW.

When the position detection signal PV is output from the Hall element HV due to the rotation of the rotor 4, the output pattern for starting control has a waveform shown in the section C. In this case, the transistor TV + and the transistor TU And the drive signals GV + and GU- are output, and the current from the DC power supply 7 flows through the transistor TV +, the coil LV, the coil LU, and the transistor TU-. Therefore,
The rotor 4 is rotated by being attracted or repelled by the coil LV and the coil LU. Similarly, by outputting a drive signal to a predetermined transistor so as to sequentially switch the combination of transistors to be energized, a rotational force is continuously applied to the rotor 4 and the rotation speed of the rotor 4 is determined. Will increase to a number. In this start control output pattern, the duty ratio is 100%, so that the drive signal output to each transistor has a mechanical angle of 120 ° in the rotation direction of the rotor 4.

The control unit 5 has a function as a rotation speed detecting means, and the control unit 5 detects the rotation speed of the rotor 4.

The rotation speed is determined by the position detection signal P
The calculation is performed based on the detection positions of U, PV, and PW, that is, from the time differences when the respective position detection signals PU, PV, and PW are detected. For example, at the same time that the rising edge of the position detection signal PU is detected,
The controller 5 measures the time Tu from the time when the rising edge is detected. Next, the position detection signal PV
At the same time when the rising edge of
Measures the time Tv from the time when the rising edge is detected. Then, a time Tu-v, which is a difference between the time Tu and the time Tv, is obtained. This time Tu-v
Means that each of the Hall element HU and the Hall element HV is 12
Since the rotor 4 is arranged with a phase difference of 0 ° and reacts with the permanent magnet 1 within a range of 180 ° around the arrangement position, the rotation time Trpm during which the rotor 4 rotates 120 ° in mechanical angle is determined. Will match. Therefore, the rotation speed of the rotor 4 can be calculated from the relationship between the rotation time Trpm and the mechanical angle. Further, as can be understood from FIG. 3, the rotation time Trpm is the time when the rotor 4 rotates 120 ° in the rotation direction by a mechanical angle, so that the on-time of the drive signal when the duty ratio is 100% is equal to the on-time. Will match. In the present embodiment, the rotation speed of the rotor 4 is calculated from the time difference when the position detection signals PU, PV, and PW are detected. However, the present invention is not limited to this. You may make it detect.

By comparing the rotation speed of the rotor 4 detected in this way with the startup determination rotation speed stored in the memory of the control unit 5 in step 3, the rotor 4 whose startup is controlled is determined. It is determined whether or not the rotation speed of the motor has reached the start determination rotation speed. At this time,
If the rotation speed of the rotor 4 is equal to or less than the startup determination rotation speed,
As shown in (2), the start control in step S2 is continued, and the rotation speed of the rotor 4 is further increased.

When it is determined in step S3 that the rotation speed of the rotor 4 has become equal to or higher than the startup determination rotation speed,
In step S4, the control of the DC brushless motor is switched from the start control to the inertia control.

In this inertia control, the DC brushless motor is rotated at a predetermined duty ratio, that is, at a duty ratio of 50% in this embodiment. For that purpose, each coil LU, LV, LW
It is necessary to control the voltage applied to the negative electrode transistors TU-, TV- and TW-, as shown in FIG. This is performed by synchronizing with the rotation speed of 4.

Therefore, the control unit 5 inputs the ON time of the drive signal output to each of the negative-side transistors TU-, TV-, TW- to the number of revolutions of the rotor 4 during the previous rotation and the control unit. The duty ratio is set to a value calculated from the duty ratio. The rotation speed of the rotor 4 is
As described above, this drive signal is output 2
In the case of the present embodiment, the number of rotations of the rotor 4 during the previous rotation is calculated from the rotation time Trpm of the rotor 4 between the rising edges of the two Hall elements. Rotation time Tbrp of the rotor 4 between the rising edges of the two Hall elements at the time
m is used.

Therefore, the ON time Ton of the drive signal output to each of the negative-side transistors TU-, TV-, TW- is a value obtained by multiplying the rotation time Tbrpm at the previous rotation of the rotor 4 by the duty ratio. . For example, in the case of FIG. 4, in the case of the drive signal GW- to the negative-side transistor TW- in which the drive signal is output over the section A and the section B, the rotation time Tbrpm is equal to the rotation time of the previous rotation of the rotor 4. Is the time from the detection of the edge of the position detection signal PU from the Hall element HU to the detection of the edge of the position detection signal PV from the Hall element HV. ON time Ton = rotation time Tbrpm × 50%
/ 100% = rotation time Tbrpm / 2. That is,
As described above, the rotation time Tbrpm is the time when the rotor 4 rotates at a mechanical angle of 120 ° in the direction of rotation, and the ON time of the drive signal when the duty ratio is 50% is 60 ° at the mechanical angle. Range. In the present embodiment, the case where the duty ratio is set to 50% is shown. However, when this duty ratio is set to various values, the rotor 4 rotates at a rotational speed synchronized with the value of the duty ratio. Because of the rotation, the negative side transistors TU-, TV-, TW
The ON time Ton of the drive signal output to the negative side is synchronized with the rotation speed of the rotor 4.

In order to match the center position of the drive signal having the on-time Ton with respect to the time axis to the center position when the duty ratio of the drive signal is 100%, the drive signal is output in the following pattern. Is done.

First, no drive signal is output from the time when the edge of the position detection signal PV from the Hall element HV, which is the reference of the section A, is detected until the rotation time Tbrpm / 4 elapses. It is rotated by its inertial force.
Next, when the rotation time Tbrpm / 4 has elapsed, a drive signal is output, and this is maintained during the ON time Ton. Next, after the ON time Ton has elapsed, the output of the drive signal is stopped. With such an output pattern, an attractive force or a repulsive force generated between the rotor 4 and each of the coils LU, LV, LW is applied to the rotation of the rotor 4 with an equal time difference. The rotation of the rotor 4 can be made smooth.

On the other hand, each positive-side transistor TU
+, TV +, TW + are duty ratios of 100 shown in FIG.
%, The ON time is the rotation time Tbr.
It is driven by a drive signal having a length equal to pm.

By such inertia control, the energization to the coil assembly 3 shown in the lowermost stage of FIG. 4 is repeated, and the ratio of the energization time to the total time of the energized state and the non-energized state, that is, the coil assembly 3 Can be set to the duty ratio of 50% input in step 1.

As described above, the on-time Ton of the negative electrode side transistor is calculated from the rotation speed of the rotor 4 during the previous rotation and the duty ratio input to the control unit 5, and is synchronized with the rotation speed of the rotor 4. Value, the conventional P
Since the DC brushless motor can be controlled without using a pulse having a carrier frequency as in the WM control, the number of times of switching of each transistor can be reduced, and the heat generated by the switching circuit 6 of the DC brushless motor can be reduced. Energy loss can be reduced.

Step 5 is for stopping the DC brushless motor. When a switch (not shown) is turned off, the output of the drive signal from the control unit 5 is stopped, and the DC brushless motor is stopped. Will be. Unless the switch is turned off, step S
Step 3 and Step S4 are repeated, and the DC brushless motor continues to rotate at a rotational speed having a predetermined duty ratio.

FIG. 5 is a time chart showing a modification of the output pattern during the inertial control shown in FIG.

In the output pattern at the time of inertia control shown in FIG. 4, only the on-time of the drive signal output to the negative-side transistors TU-, TV- and TW- is shortened at a predetermined duty ratio. However, in the output pattern shown in FIG. 5, the ON times of both the drive signals output to the positive-side transistors TU +, TV +, TW + and the negative-side transistors TU−, TV−, TW− are set to a predetermined duty ratio. To be shortened at the rate of

In this case, in step S1, the control unit 5
In order to make the duty ratio inputted to the drive signal ON time equal to the duty ratio of the voltage applied to the coil assembly 3 as a result of shortening the ON time of the drive signal, the duty used to actually set the ON time of the drive signal The ratio is converted as (duty ratio% input to the control unit) / 2 + 50%.

This is because the voltage is applied to the coils LU, LV, LW only when the positive side transistors TU +, TV +, TW
+ And the negative side transistors TU−, TV−, TW− are both in the ON state, so that the positive side transistors TU +, TV +, TW + and the negative side transistors TU−, TV−
When the on-time of both the-and TW- is shortened, the duty ratio of the voltage applied to the coils LU, LV and LW becomes the same as the effect of shortening the on-time of both transistors. is there.

For example, in the case shown in FIG. 5, the duty ratio input to the control unit 5 in step S1 is 50%. However, the duty ratio used to actually set the ON time of the drive signal is 50%. / 2 + 50% = 7
It is 5%.

The energization of the coil assembly 3 is repeated by the same steps, and the ratio of the energization time to the total time of the energized state and the non-energized state, that is, the duty ratio for the coil assembly 3 is input in step 1. The duty ratio can be set to 50%.

As can be seen from FIG. 5, the cycle of repeating the energization of the coil assembly 3 is shorter than that shown in FIG. Therefore, as in the present modification, the ON times of both the drive signals output to the positive-side transistors TU +, TV +, TW + and the negative-side transistors TU−, TV−, TW− are set to a predetermined duty ratio. By reducing the ratio, the rotor 4 can be smoothly rotated.

The present invention is not limited to the above embodiment, and it goes without saying that various changes can be made without departing from the spirit of the present invention. For example, the drive signal synchronized with the rotation speed of the rotor 4 shown in FIGS. 4 and 5 has a single rectangular waveform having one rising edge and one falling edge, but is not limited thereto. Any waveform may be used as long as a predetermined ON time can be obtained. For example, as shown in FIGS. 6A and 6B, the waveform is formed by two rectangular waveforms, and the sum of each ON time is equal to the predetermined time. You may make it become.

In this embodiment, the DC brushless motor is of a three-phase two-pole type. However, the present invention is not limited to this, and any number of phases and poles may be used.

[0058]

According to the present invention, the on-time of the drive signal for driving the switching element of the inverter section is synchronized with the rotation speed of the rotating body, so that the switching operation of the switching element at the time of control is performed. Since the number of times can be reduced, overheating and energy loss of the switching element of the DC brushless motor can be reduced.

Further, the on-time of both the drive signal for driving the positive switching element and the drive signal for driving the negative switching element are controlled so as to be synchronized with the rotation speed of the rotating body. In addition to the effect, the rotating body can be further smoothly rotated.

[Brief description of the drawings]

FIG. 1 is an explanatory view schematically showing a configuration of a DC brushless motor according to an embodiment of the present invention.

FIG. 2 is a flowchart for explaining control of the DC brushless motor shown in FIG.

FIG. 3 is a time chart showing an output pattern at the time of start control of the DC brushless motor shown in FIG. 1;

FIG. 4 is a time chart showing an output pattern at the time of inertia control of the DC brushless motor shown in FIG. 1;

FIG. 5 is a time chart showing a modification of the output pattern at the time of inertia control shown in FIG. 4;

FIGS. 6A and 6B are explanatory diagrams showing modified examples of the drive signals shown in FIGS. 4 and 5. FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Permanent magnet 2 Motor body 3 Coil assembly 4 Rotor 4a Rotary shaft 5 Control part 6 Switching circuit 7 DC power supply 7a Positive terminal 7b Negative terminal LU, LV, LW Coil HU, HV, HW Hall element PU, PV, PW Position detection Signal TU + Positive side transistor for U phase TV + Positive side transistor for V phase TW + Positive side transistor for W phase TU- Negative side transistor for U phase TV- Negative side transistor for V phase TW- W phase Negative side transistor SU, SV, SW Series circuit D diode GU +, GU- drive signal GV +, GV- drive signal GW +, GW- drive signal

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Kenya Yanagihara 1-268, Hirosawa-cho, Kiryu-shi, Gunma Mitsuba F-term (reference) 5H560 AA03 AA07 BB04 BB12 DA02 DA19 DB20 EB01 EC02 RR07 RR10 UA02

Claims (5)

[Claims] 1. A DC brushless motor including a stator having a coil assembly formed by coils of a plurality of phases and a rotating body having a permanent magnet, wherein: a position detecting means for detecting a position of the rotating body; A rotational speed detecting means for detecting a rotational speed of the rotating body based on a position detected by the position detecting means, and an on-time of a drive signal of a switching element of an inverter unit is controlled in synchronization with the rotational speed of the rotating body. DC brushless motor having a control means. 2. The DC brushless motor according to claim 1, wherein energization of said coil assembly is repeated by said drive signal. 3. The DC brushless motor according to claim 1, wherein the on-time is calculated from a rotation speed of the rotating body during a previous rotation and a duty ratio input to the control means. DC brushless motor. 4. A stator having a coil assembly formed by coils of a plurality of phases, a rotating body having a permanent magnet, a position detecting means for detecting the position of the rotating body, and a position detecting means for detecting a position of the rotating body. DC brushless having a rotation speed detecting means for detecting the rotation speed of the rotating body based on the rotation speed, and an inverter unit including a positive switching element connected to a positive terminal of the power supply and a negative switching element connected to the negative terminal. A method for controlling a motor, comprising: detecting a rotation speed of the rotating body during a previous rotation; calculating an on-time of a drive signal from the rotation speed and a predetermined duty ratio; A method for controlling a DC brushless motor, wherein the output is provided to at least one of a switching element and a negative switching element. . 5. The control method for a DC brushless motor according to claim 4, wherein a start control for operating the rotating body from a stopped state to a start determination rotation speed is performed.