JPH02276491A - Controlling method for brushless dc motor - Google Patents

Abstract

PURPOSE:To control the rotation of the title motor without employing any rotor position detecting element by a method wherein the supply of current to one phase is limited temporarily for a predetermined period to measure the rise-up condition of the current while the positions of the magnetic poles of the rotor are detected based on the rise-up condition of the current. CONSTITUTION:A rise-up time 58 necessary for the rise-up of the value of current to the specified value of the current becomes minimum when different poles are opposed correctly. Accordingly, the positions of the different poles of the rotor can be judged whether they are opposed correctly by measuring the rise-up time 58. The position of the rotor is detected by measuring the rise-up time 58. When the rotor is arrived at a proper position, a phase, through which driving current is conducted, is switched (commutation) whereby the title motor may be rotated.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a brushless DC motor, particularly a brushless DC motor suitable for rotating a magnetic disk in a magnetic disk device.
This invention relates to a control method for brushless DC motors that do not use magnetic sensors.

[Conventional technology]

The brushless DC motor according to the present invention is highly efficient, does not require maintenance of brushes, and is highly reliable, so it can be used as a spindle motor for magnetic disk drives,
It is used to drive the rotary head of R, and is used in various fields as a power source.

Instead of using brushes, conventional brushless motors use
The position of the rotor facing the stator is detected using a rotor position detection element such as a Hall element, and the winding (phase) through which the motor drive current flows is switched depending on the detected position.

However, a method for controlling a brushless DC motor has been proposed in which the position of the rotor is electrically detected without using this rotor position detection element.

For example, in Japanese Patent Laid-Open No. 59-162793, the position of the rotor is detected by utilizing the back electromotive force generated in the drive winding as the rotor rotates.

Furthermore, in Japanese Patent Application Laid-open No. 63-69489, a high-frequency current that forms short current pulses is sequentially passed through each winding at predetermined intervals of a rotating motor, and the peak of the current that actually flows through each winding is detected. The rotor position is detected by comparing the amplitude values.

[Problem to be solved by the invention]

In the conventional method using a back electromotive force signal, it is detected whether or not a back electromotive voltage is generated in a phase through which a drive current is passed, and the winding through which the drive current is passed is switched. However, the generation of a back electromotive voltage means that the ideal commutation position has been exceeded, and therefore there is a problem in that brake torque is generated and rotational efficiency is deteriorated.

In addition, in the method of passing current pulses through each winding, the power supply is stopped while the windings (phases) to be driven are being energized, and current pulses are passed through all other windings (phases). Current also flows through the phase that induces rotational force, increasing fluctuations in the driving torque.

Furthermore, in order to detect the position of the rotor, the power supply to the drive winding must be temporarily stopped, resulting in a problem of poor efficiency. In addition, as the motor rotation speed increases, the ratio of the rotor position detection time to the power supply time to the drive winding (during which the power supply to the drive winding is stopped) increases, resulting in insufficient driving power in the high rotation range. There is a problem with becoming. For example, according to calculations made by the inventors, when a 4-pole 3-phase motor is rotated at 360 rpm, the current flowing through one drive winding is 1.39 m5. Of these, to detect the rotor position, for example, if a high frequency pulse of 0.2u+S is sequentially passed in each measurement for a total of 6 measurements, 2 times for positive and negative for each 3 phases, the actual time to flow the current to the drive winding is 1 .39-
(0,2X6) =0.19m5. That is, more than half of the time of current flowing through the drive winding is spent detecting the rotor position, resulting in a significant drop in efficiency and a problem of insufficient torque.

A first object of the present invention is to provide a method for controlling a brushless DC motor that can control rotation without using a rotor position detection element.

A second object of the present invention is to provide a method for controlling a brushless DC motor that has high rotational efficiency and reduces fluctuations in drive torque even in a high rotation range.

A third object of the present invention is to provide a highly reliable brushless DC motor control method.

A fourth object of the present invention is to provide a method for controlling acceleration/deceleration of a brushless DC motor with a fast response speed.

A fifth object of the present invention is to provide a method for controlling a brushless DC motor that performs acceleration/deceleration control using servo signals recorded in advance on a magnetic disk.

[Means and operations for solving the problems] In order to achieve the above object, the present invention is realized in a brushless DC motor having a rotor having a magnet with a plurality of magnetic poles and a winding having a plurality of phases. . In order to rotate the brushless DC motor, a drive current is passed through each phase at predetermined intervals. The drive current is sequentially applied to each phase, and the rotor rotates in synchronization with this switching.

Regarding the control of the brushless DC motor according to the present invention,
Control is preferably divided into three modes from the time of startup to the time of steady rotation. The first mode is a mode in which control is performed in the low speed rotation range from startup.

The second mode performs control from a low speed rotation range to steady rotation, and the third mode performs constant speed control during steady rotation.

In the first mode, the drive current supplied to one phase is temporarily limited for a predetermined short period of time. After the period has elapsed, the limited drive current begins to flow again in the same phase. The rising state of the drive current when it starts flowing is measured.

There are several possible methods for measuring the rising state.

For example, a method that measures the rise time for the current value to reach a specified amount from 0'', or a method that uses a clock signal to measure how many times the clock signal is generated until the current value reaches the specified amount from 0''. There is.

Next, based on the measured rising state, the type and position of the magnetic pole directly facing the phase through which the drive current is flowing is detected. The release time of the drive current changes depending on the type and position of the magnetic pole facing the phase. The drive current rises in the shortest possible time when the magnetic field generated by passing the drive current is directly opposed to the magnet of the opposite polarity. Based on the detected rotor position, the drive current is transferred to the next winding (phase).
It is determined whether to switch (commutation) to or not. If commutation is determined, the drive current is switched to the next winding. If it is determined that there is no commutation, the rotor position detection is performed again after a predetermined period of time has elapsed.

In the second mode, immediately after commutation, the time required for the drive current to rise after switching to the next phase is measured. Based on this rise time, the time period during which the drive current is applied to that phase (current application time) is determined.

After the energization time has elapsed, commutation to the next phase is further performed.

In the third mode, first, the rotation speed of the brushless DC motor is measured. Various methods can be used to measure the rotational speed, but in brushless DC motors for magnetic disk drives, it is preferable to measure the rotational speed using servo signals recorded on the magnetic disk.

When it is determined that the rotational speed is high, a current (brake current) substantially equal to the starting current is passed for a predetermined interval, and the brake is applied by changing the commutation timing. When it is determined that the rotation speed is low, the rotation speed of the motor is increased by flowing an accelerating current. These currents are not switched in an analog manner, but are controlled by switching between the steady current, brake current, and acceleration current in a time-sharing manner.

〔Example〕

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

FIG. 2 is a perspective view of a magnetic disk device suitable for applying the brushless DC motor of the present invention.

31 is a spindle motor, and a magnetic disk disk 32
This is a so-called in-hub type motor in which a hub on which a motor is mounted and an outer casing of the motor are integrated, and to which the brushless DC motor according to the present invention is applied.
3 is a magnetic head for recording/reproducing signals on the magnetic disk disk 32; 34 is a load spring for pressing the magnetic head 33 against the magnetic disk disk with a constant force; 3;
5 is a head arm, 36 is a shaft, and the head arm 35 is configured to swing around the shaft 36. 37 is a voice coil motor and a head arm 35
It is for driving.

FIG. 3 is a sectional view of a brushless DC motor according to an embodiment of the present invention. The flange 40 has an integral structure with a bearing tube 47 for fixing a bearing 46. The rotor 41 is a rotating part of the motor, and in this example also serves as a hub on which the magnetic disk disk 32 is mounted. Rotor 41 is fixed to shaft 45. Permanent magnet 42 is fixed to the inner circumference of rotor 41. The stator 43 generates a magnetic field by passing a current through the windings 48, and is made of laminated iron plates. The shaft 45 is rotatably held by a bearing 46. Lead wire 4
Reference numeral 9 is for supplying a drive current for rotating the motor to the winding 48, and is connected to a motor control circuit (described later) through a connector 50.

FIG. 4 is a diagram for explaining the structure of the rotor and stator of the brushless DC motor according to this embodiment. The permanent magnet 42 is a cylindrical magnet and has four poles.

Stator 43 has three phases. The motor of this example is
This is a so-called 6-ball, 3-phase motor in which two balls become N poles when the l-phase is energized, as shown in FIG.

FIG. 5 is a diagram for explaining that when current is passed through one phase of the stator in the state shown in FIG. 4, the rise time of the current in that phase changes depending on the position of the opposing permanent magnet 42. The horizontal axis indicates the rotational position of the rotor. For example, in FIG. 4, this indicates how many times the reference point 52 of the rotor deviates from the center position 51 of the energized phase (in this case, the deviation between the north pole and the south pole). The vertical axis indicates the time required for the current to rise from 0 [A] to a specified current value when a current is applied to a certain phase.

As is clear from FIG. 5, the inventors have found that the rise time 58 of the drive current becomes the minimum when the permanent magnet 42 facing the stator 43 with a certain polarity comes to the center position of the opposite polarity. discovered. It was also found that the rise time 58 of the drive current increases again as the polarity approaches the same polarity from that state.

FIG. 6 is a diagram showing the rising state of the drive current from 0 to the steady-state value. In this case, the rise time 58 required for the current value to rise to the specified current value becomes the minimum when the polarity is directly opposed to the opposite pole as explained in FIG. Therefore, by measuring this rise time 58, it is possible to determine whether or not the different poles of the rotor are in positions facing each other. The present invention detects the rotor position by measuring this rise time 58. and,
When the rotor reaches the appropriate position, the phase of the drive current is switched (commutation) to rotate the motor.

Next, a motor control circuit according to this embodiment will be explained using FIG. 1. The motor 31 is a magnetic disk disc 32
For example, it is a 6-volume, 3-phase motor. This motor is controlled in the first mode, which controls from stop to low speed rotation, and from low speed rotation to steady rotation (for example, 3
．． Control is divided into three modes: a second mode that controls rotation up to 600 rPm, and a third mode that controls steady rotation.

The oscillation circuit 1 is a circuit that generates a reference signal for controlling the rotation of the motor 31, and includes an oscillator 2 made of a crystal oscillator and a frequency divider 3 for generating a desired reference signal.

The signal selection circuit 4 has the first . Second. A reference signal to be input is selected according to the third mode. Information regarding the control mode is stored in the state control circuit 18 of the controller 16.

The timing generator 5 determines the output line of the drive current of the power supply switching circuit 6 according to the reference signal selected by the signal selection circuit 4. That is, it is determined whether each winding 48 is connected to the power supply side, return side, or disconnected.

In addition to selectively supplying a drive current to each winding 48, the power supply switching circuit 6 short-circuits each winding according to an instruction from the brake instruction circuit 20.

The current limiting circuit 21 controls the drive current at fixed intervals, for example 10 μs, in order to detect the position of the rotor in the first mode.
Stop for a while. The current detection circuit 22 detects a state in which the drive current stopped by the current limiting circuit 21 or the drive current switched by the power supply switching circuit 6 rises again.

The position detector 11 measures the current rise time 58 from the output signal of the current detection circuit 22. The position detector 11 includes a clock circuit 12 .

Here, a method for measuring the rising state of the drive current 56 will be explained using FIGS. 6 and 7 (1) to (3).

In FIG. 6, the clock circuit 12 calculates the rise time 58 for the drive current 56 to return from the minimum value (=O) to the specified current value 57.
Measured by

In FIG. 7(a), instead of measuring the rise time 58, a measurement command 59 is generated as a clock signal, and the timer circuit 12 counts the number of measurements until the current value reaches the specified value 57, and the time is measured using this count value 60. This is to act on your behalf. Since this measurement is performed multiple times in one phase during rotation of the motor, the transition of the rise time 58 is determined based on these results. Commutation to the next phase occurs when this rise time reaches the minimum time value (the time value when the opposite magnetic pole reaches the center position 51 in FIG. 5).

FIG. 7(b) shows a counter value of 3 of 60 using another measurement method.
This is a method of measuring the 5th and 5th times and calculating the rise time 58 from the current values 61 and 62 at that time. The average value of these current values is determined, and when this average value exceeds a predetermined runaway current value, commutation to the next phase is performed.

FIG. 7(C) shows yet another measurement method. This is the seventh
The measurement shown in Figure (b) is performed by selecting between two arbitrary points using a timer (not shown) instead of a clock signal. That is, a timer is set when the drive current 56 rises, the first measurement is performed after T1, and the second measurement is performed after T.

Referring again to FIG. 1, the measured values measured by the position detector 11 are input to the controller 16.

The calculation circuit 17 calculates the next time to switch the drive current based on the measured value. When the switching time is reached, the controller 16 outputs a switching signal to the signal selection circuit 4.

The magnetic head 33 reads out a servo signal recorded in advance on the magnetic disk disk 32, and the disk reading circuit 10 increases the servo signal and outputs it to the position detector 13. The counter circuit 14 of the position detector 13 counts the servo signals and outputs them to the speed generation circuit 15. The speed generation circuit 15 determines the rotational speed of the motor 31 based on the servo signal, and recognizes whether it is faster than a predetermined speed (number of rotations). The position detector 13 and speed generating circuit 15 are mainly used in the third mode. Here, if it is recognized that the speed is fast, the brake instruction circuit 20 issues a brake instruction to the power supply switching circuit 6, and the motor 31 is braked while the instruction is issued. If the speed is recognized as slow, the drive current instruction circuit 19 issues an acceleration command to the current limiting circuit 21, and the power supply switching circuit 6 causes the acceleration current to flow. If the speed is determined to be appropriate, the steady current continues to flow. The speed of the motor 31 is controlled by switching the braking operation and the acceleration operation of the motor 31 in a sector-by-sector time division manner to obtain a predetermined rotational speed.

Next, control operations in the first to third modes of the brushless DC motor according to this embodiment will be explained using FIGS. 8 to 16.

FIG. 8 is a diagram for explaining current switching timing in the first mode of the motor according to this embodiment. In this embodiment, a 3-phase motor with 4 magnetic poles and 6 balls is used, and FIG. 8(a) shows the coil terminal voltage of the U phase. In this motor, the drive current to each winding is switched every 1712 rotations.

FIG. 8(b) shows the timing at which the current limiting circuit 21 limits the current signal. When the current limit signal is issued by the current limit circuit 21, the drive current 56 decreases to approximately zero. Next, when this current restriction is released, the drive current 56 rises rapidly as shown in FIG. 8(C). This rising state changes depending on the position of the rotor, as shown in FIG.

The current detection circuit 22 measures the rising state of the current value. At this time, the position detector 11 issues a measurement command as shown in FIG. 8(e) and detects the position of the rotor at this time. This figure shows an example of measurement using the method shown in FIG. 7(3). FIG. 7(f) shows the state of power supply to each phase when the rotor position detection operation is performed. In this state, data is collected based on the measurement command issued by the clock circuit 12. By analyzing this data, the position of the rotor 41 with respect to the winding 48 can be determined, and if the proper commutation position is reached after several measurements, a commutation signal is issued.
The energization to the next winding (phase) 48 is switched.

FIG. 9 shows an enlarged view of the measurement location in FIG. 8, and shows how the measured current value changes and the difference between the two values changes as the field rotor moves. This figure shows the measured current values when ten measurement commands 59 were issued. In this case, the current values are high in measurements 1 and 2, and the difference between the two current values is also small. This state is before the proper position for commutation, that is, before the S pole reaches the center position 51 in FIG. At measurements 7 and 8, the current value becomes relatively small, and 2
The difference between the two current values becomes large. This position is an appropriate position for the commutation timing, that is, the S pole is at the center position 51 in FIG.
It has reached a state of . If the current is commutated at this time, the current can be commutated before the back electromotive force is generated. In measurements 9 and 10, the back electromotive force is added, the current value increases, and the difference between the two values becomes smaller than in measurements 7 and 8.

Incidentally, when the winding and the magnet approach each other, only driving torque is generated, but when they move away from each other, a braking effect occurs due to the generation of a back electromotive voltage, so it is desirable to perform commutation before the generation of the back electromotive force.

In addition, when the rotation becomes high speed and the commutation timing is desired to be early, commutation can be performed during measurements 5 and 6, and the conduction state of the drive current can be freely adjusted by position detection.

FIG. 10 is a flowchart of the position detection operation in the first mode. As the position detection method, the method shown in FIG. 8 is used here.

First, it is determined whether the timer has expired or not, and if the timer has not expired, wait until the timer has finished (step 1o1).

This timer measures the timing of position detection. When the timer expires, that is, it is time for the next position detection, the drive current 56 is decreased by 10 μs (step 10).
2). After that, when the drive current 56 starts to rise (step 103), the set time T1 of the timer 63 is set to 20 μs (step 104). When 18 hours have elapsed, a measurement command 59 is issued, and the drive current 56 is measured (steps 105 and 106), and then the timer 63 is set for the time T.
2 is set to 20 μs (step 107). After 18 hours have elapsed, a measurement command 59 is issued and the drive current 56 is measured (steps 108, 109). Next, step 1
The position of the rotor is detected from the difference between the values of the drive current 56 measured at steps 110 and 109, and it is determined whether the rotor has passed the commutation position (steps 110 and 111). If the commutation position has not yet been passed, set the timer to 40 μs as the timing for the next position detection in step 115.
), return to step 101. When the commutation position has been passed, the commutation is immediately performed (step 112), the commutation time is determined from the motor rotation speed (step 113), and the timer is set to 1 to 60+ns (step 114).

Next, with reference to FIGS. 11 and 12, a description will be given of control in the second mode from when the motor is started until it reaches a steady rotational speed.

FIG. 11 is a time chart of switching the excitation phase of the motor.

In the first mode, position detection was performed by limiting the drive current 56 at regular intervals, but in the second mode, the current was not limited and the drive was performed during commutation every 1/12 rotation of the rotor. The rising state of the current 56 is measured, and the next commutation timing is determined according to this rising state.

FIG. 11(a) shows the waveform of the drive current 56.

The drive current 56 is once reduced to a specified current value of 90 or less by commutation every 1/12 revolution. If the motor has characteristics such that the drive current does not fall below the specified current during commutation, the current limiting circuit 2
1, the current may be temporarily cut when commutation is performed. When the energization time shown in FIG. 11(C) has elapsed, a commutation signal as shown in FIG. 11(d) is generated to commutate to the next phase. When commutation occurs, the drive current 56 shifts from one phase to the next phase as shown in FIG. 11(b), and during this commutation, the drive current 56 temporarily drops. Next, the drive current 56 rises again to the specified current value, and the time until it reaches this specified current value 90 is measured to determine the energization time in that phase. During this time, the power to the motor drive windings is U phase, ■ phase, and W.
Directions are given by the combinations of the phases and their respective pairs of the X phase, Z phase, and Z phase, and current commutation, etc. are controlled. Figure 11 (
In f), the U-W phase is turned on when it is Lo, and the X-Z phase is turned on when it is Hi.
This is the phase current.

FIG. 12 is a flowchart showing the motor control operation in the second mode. First, it is determined whether the timer for measuring the energization time has expired.

When the timer expires, that is, when the commutation time comes, commutation is performed (steps 121 and 122).

Next, measurement of the rise time of the drive current value 56 is started (step 123). Drive current value 56 is specified current value 59
Once reached, measure the rise time 58. Step 1
24, 125), and the rotor position is detected (step 126).

Next, the energization time is calculated based on the detected rotor position. The energization time is determined by (previous energization time x (i 10 rotor position correction value 10 rotation speed increase correction value)) (Step 127
). Here, the rotor position correction value is a correction value determined depending on whether the commutation is earlier or later than the appropriate timing, and is determined based on the rotor position detection in step 126. The rotation speed increase correction value is a correction value determined according to an increase or decrease in the rotation speed of the motor. The determined energization time is set in the timer and the process returns to step 121.

Next, the third mode, that is, the motor control method when the motor is in steady rotation will be explained using FIGS. 13 to 16.

FIG. 13 is a flowchart showing a control procedure for the motor during steady rotation, for example, at 3600 rpm.

First, the rotational speed of the motor is measured at predetermined intervals during steady rotation (step 131).There are various methods of measuring the rotational speed, but in this embodiment, the rotational speed of the magnetic disk disk 3 which is the object to be rotated is measured.
The measurement is performed using the sector servo signal recorded in advance in step 2. Normally, during steady rotation of the motor, a smaller drive current flows than when the motor is started, for example, a current of 0.4 A in a 3.5-inch magnetic disk motor.

Next, it is determined whether the measured rotation speed matches the reference rotation speed (step 132). When the rotational speed is higher than the reference rotational speed, the time to apply the brake is calculated (step 133), and the brake current is applied for a predetermined sector interval (step 134). Similarly, when the rotational speed is low, the acceleration time is calculated (step 135), and the acceleration current is passed for a predetermined sector interval (step 136). The accelerating current is a drive current larger than the steady current, for example a drive current of 1.5A.

Next, a method of setting the braking time and acceleration time will be explained using FIG. 14. The magnetic disk disk 32 has a recording area divided into a plurality of concentric tracks, and each track is divided into a plurality of sectors (not shown). Servo information is prerecorded at the beginning of each sector, and by reading the servo information with the magnetic head 33, the beginning position of each sector can be recognized.

The plurality of sectors are arbitrarily divided into N sectors 141, and acceleration/deceleration control is performed at K sector cycles. Among these sectors, for example, a brake current 142 is applied while passing through sector #1 to sector #3, and a steady current 143 is applied during the remaining period. Brake amount is brake current 142
Adjust by increasing or decreasing the time (number of sectors) to flow. During acceleration, an acceleration current may be applied instead of the brake current 142.

Various methods can be applied to flow the brake current 142.

■Turn off the drive current. The rotational speed decreases due to air resistance, friction, etc. (2) Reduce the drive current so that it is below the current that can maintain steady rotation (for example, 0.2A), and gradually decelerate. ■Short between the windings and apply the brakes using the current caused by the back electromotive force. ■Flow a large current equivalent to the accelerating current,
Also, the commutation timing is slightly delayed from the appropriate position. Powerful braking can be applied by generating a back electromotive force.

This method is unique to the motor according to this embodiment, in which the commutation timing of the motor can be freely changed using software.

Next, the principle of the brake operation described in (2) above will be explained using FIG. 15. FIG. 15(a) shows the relationship between rotor position and drive current. The drive current 151 rises rapidly immediately after commutation (range 152). The current value remains at the specified value until the magnet facing the facing position, that is, the magnet facing the magnetic pole through which the drive current 151 is flowing reaches the center of the magnetic pole (range 153). After passing the directly facing position, a back electromotive force is also added and the drive current 151 increases (range 154).

The first one shows the driving torque generated by the motor at this time.
5(b). As can be seen from this figure, a positive torque of 156 is generated until the rotor reaches the facing position.
After passing the facing position, negative torque 157 due to back electromotive force is generated.
That is, brake torque is generated. During steady rotation, when the winding reaches the facing position, the current is commutated to the next winding to eliminate the influence of the negative torque 157. However, in this embodiment, the commutation position is delayed from the facing position so that the negative torque 157 is actively used for braking operation. In general, in brushless DC motors using Hall elements, commutation always takes place in the facing position, so negative torque 157 cannot be used.
In the motor according to this embodiment, the negative torque 157 can be easily applied to the braking operation by simply selecting the commutation from the 7th and 8th positions in FIG. 9 to the 9th and 10th positions.

Next, details of the third mode will be explained using the control flowchart shown in FIG. This figure shows a flowchart for speed control by selecting three drive current values.

In addition to the steady current 143, the accelerating current and the braking current 1
42 is used.

When it is necessary to increase the speed of the motor, m out of n sectors
(<n) An accelerating current is passed between sectors, and a steady current is passed between the remaining nm sectors. Similarly, when it is necessary to decelerate the motor, a brake current is passed between S (≦Ω) sectors among 0 sectors, and a steady current is passed between the remaining Ω-s sectors.

In step 200, N indicates the number of remaining sectors in which the current flowing to the motor continues to flow without being switched. If the current is N, then N=N-1 and the normal current is maintained while passing between one sector (step 216).

If N=1, it is time to switch modes, so the drive current value is 56.
can be switched to either braking current, accelerating current or steady current.

In step 202, the presence or absence of a brake flag is determined. The presence of the brake flag indicates that the brake operation has been performed (completed), and the brake current is released and returned to the steady state current (steps 218 and 220). Then, the number of sectors N (=Ω-8) through which the steady current flows is set, and the brake flag is released (steps 222, 224).

If there is no brake flag in step 202, the program proceeds to step 204 and checks whether there is an acceleration flag. The presence of the acceleration flag indicates that an acceleration operation was performed (completed).
The accelerating current is canceled and the steady current is restored (step 226). Then, the number of sectors N in which steady current flows
(=n-m) and cancels the acceleration flag (steps 228, 230).

If there is no acceleration flag in step 204, then a measurement command is issued to measure the rotational speed of the motor 31 (step 206). Next, a numerical value counting the time interval of sector servo signals generated for each sector is read (step 208). In step 210, D and C (count number when rotating at the lower limit of allowable rotation speed) are compared, and if it is DEC, it is recognized that the rotation speed is slow, and the process proceeds to step 232, where an acceleration current is applied and an acceleration flag is set. is set, and the number of sectors N (=m) through which the accelerating current flows is set (steps 234, 236).

If D≦C, the process advances to step 212. Step 212
Then, compare D and C'' (count number when rotating at the upper limit of allowable rotational speed), and if DEC', it is recognized that the rotational speed is fast, proceed to step 238, apply the brake, A brake flag is set and N is set (steps 240, 242), where N is S and is the number of sectors on which the brake is applied.

If D≧C°, the process advances to step 214. Step 21
At No. 4, the speed is within the allowable range, so normal current is applied.

Although the embodiments have been described above with reference to the drawings, the present invention can be modified in various ways. For example, in this embodiment, the motor was controlled in three modes, first to third, but it is also possible to control the motor in only two modes, the first mode and the third mode.

Further, in the third mode, the sector servo signal of the magnetic disk is used to measure the speed of the rotating object, but any speed signal obtained from the rotating object or other object may be used. Also, a special speed detector may be provided.

〔Effect of the invention〕

According to the present invention, a brushless DC motor can be controlled without using a rotor position detector such as a Hall element. Furthermore, since a rotor position detector is not used, the motor can be made thinner and reliability is improved. Furthermore, since the commutation timing can be arbitrarily changed by software control, precise control is possible.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing a control circuit of a brushless DC motor according to an embodiment of the present invention, FIG. 2 is a perspective view of a magnetic disk drive using a brushless DC motor according to this embodiment, and FIG. A cross-sectional view of the brushless DC motor according to the embodiment, FIG. 4 is a diagram for explaining the positional relationship between the rotor and stator of the motor in FIG. 3, and FIG. 5 is a diagram showing the position of the rotor and the rising state of the drive current. , Fig. 6 is a diagram showing the rising state of the current when the drive current flows, and Fig. 7 (a
) to (C) are diagrams showing a method of measuring the rising state of the drive current, Figure 8 is a timing diagram showing control in the first mode, and Figure 9 explains the transition of the measured current value in Figure 8. Figure 10 is a control flowchart for the first mode, Figure 11 is a timing diagram showing control in the second mode, Figure 12 is a control flowchart for the second mode, and Figure 13 is a control flowchart for the third mode. A flowchart showing the basic control principle of the mode, FIG. 14 is a diagram for explaining the brake operation control method, FIGS. 15(a) and (b) are diagrams showing the relationship between rotor position, drive current, and drive torque. 1st
FIG. 6 is a control flowchart of the third mode. 31...Motor, 56...Drive current, 58...Rise time. The first closure of the first L Law 21L! (rαd) 萬庬萬/2 Genko block number 151! 1 (mountain)

Claims (10)

[Claims] (1) The rotor is equipped with a rotor having a magnet with multiple magnetic poles and a winding with multiple phases, and the rotor is driven by passing a current for driving the rotor while sequentially switching between the phases at predetermined time intervals. A method for controlling a brushless DC motor, which is characterized in that the brushless DC motor is controlled by the following steps from startup to steady rotation speed; Temporarily limiting the supply of current to the one phase that is flowing for a predetermined period; flowing the limited current again to the same phase and measuring the rising state of the current when the current starts flowing. Step: Detecting the position of a magnetic pole of the rotor located opposite to the phase through which the current is flowing, based on the measured rising state of the current; A step of determining whether or not to switch to the next phase. When it is determined that the power supply should be switched to the next phase, the current flowing phase is switched to the next phase, and when it is determined that the power supply is not to be switched to the next phase, the current is switched to the next phase. Repeating each of the above steps after an interval. (2) The step of measuring the rising state of the current includes measuring the rising state of the current by measuring the time it takes for the current to rise from 0 to a predetermined current value. How to control a brushless DC motor. (3) The step of measuring the rising state of the current is performed by measuring how many times the clock signal is generated until the current value rises from 0 to a predetermined current value using a clock signal. 2. The method of controlling a brushless DC motor according to claim 1, further comprising measuring a rising state of the brushless DC motor. (4) The step of measuring the rising state of the current uses a clock signal, and the current value when the nth (n≧1) clock signal is generated and the current value when the n+kth (k≧1) clock signal is generated. 2. The method of controlling a brushless DC motor according to claim 1, wherein the rising state of the current is measured by determining an average value of the current values when the current rises. (5) The step of measuring the rising state of the current includes the current value after T1 time has elapsed since the current is limited, and the current value after T2
2. The brushless DC motor control method according to claim 1, wherein the rising state of the current is measured by calculating an average value of the current values after a time has elapsed (T1<T2). (6) The step of detecting the position determines that a magnet that generates a magnetic field in the opposite direction to the magnetic field generated in that phase is located when the current rises in the shortest time. A method for controlling a brushless DC motor according to item 1. (7) The method for controlling a brushless DC motor according to item 1, wherein in the step of determining, it is determined that the phase in which the current flows is to be switched when the rise time of the current is earlier than a certain reference value. (8) The rotor has a rotor having a magnet with a plurality of magnetic poles and a winding having a plurality of phases, and the rotor is driven by passing a current for driving the rotor while sequentially switching the phase to the phase at a predetermined time interval. A method for controlling a brushless DC motor, characterized in that the brushless DC motor is controlled by the following steps from startup to steady rotation speed; a step of switching the phase in which current flows from one phase to the next; measuring the rise state of the current in the next phase; determining the energization time for passing the current in that phase according to the measured rise state; and returning to the first step after the lapse of the energization time. (9) A magnetic disk on which servo information is written, a brushless DC motor that drives the magnetic disk at a constant rotational speed, a magnetic head for reading the servo information on the magnetic disk, and a servo that has been read. A method for controlling a motor of a magnetic disk device having a detection circuit that detects the position of the magnetic disk based on information, characterized in that the motor is controlled at a constant speed by the following steps; Setting three current values: a first current value, a second current value to be supplied to the motor when accelerating the motor, and a third current value to be supplied to the motor when decelerating the motor. , calculating the rotational speed of the motor based on the detected rotational position of the magnetic disk; determining whether the calculated rotational speed is higher or lower than a predetermined rotational speed; and the determined rotational speed. a step of switching the first to third current values in a time-sharing manner according to the current value; (10) It has a rotor equipped with a permanent magnet arranged with a plurality of magnetic poles, and a stator equipped with a winding wound so as to form a plurality of phases, and the plurality of phases are sequentially switched. A control device for a brushless DC motor that rotates the rotor by supplying current to the windings, comprising: a first circuit that selectively supplies current to the windings;
a second circuit for temporarily stopping the supply of current to the phase to which current is being supplied by the circuit; and after the supply of current is stopped, the first circuit again supplies current to the phase. a third circuit that counts the time until the value of this current reaches a predetermined value when the current is supplied; and a third circuit that is in a predetermined positional relationship with the phase when the third circuit counts the predetermined value. a fourth circuit that directly or indirectly detects the position of the magnetic pole of the rotor; and according to the detection result of the fourth circuit, the first circuit is controlled to determine whether or not to supply current to the next phase. A control device for a brushless DC motor, comprising a fifth circuit for determining.