GB2235098A

GB2235098A - Spindle motor control arrangement

Info

Publication number: GB2235098A
Application number: GB9017192A
Authority: GB
Inventors: Akio Nakagawa; Junichi Ikeda
Original assignee: Tokico Ltd
Current assignee: Tokico Ltd
Priority date: 1989-08-18
Filing date: 1990-08-06
Publication date: 1991-02-20
Also published as: DE4025087A1; GB9017192D0; JPH0378499A

Abstract

A spindle motor has a rotor (1a, Fig 1); a magnetic disk (3) disposed on the outer periphery of the rotor; a multiphase motor coil L1-L4 supplying rotation power to the rotor following excitation by drive current; a power supply 7, 8 which supplies the drive current to the motor coil in phase; a rotation monitor (10, Fig 4) which monitors the state of rotation of the rotor and outputs monitoring signals; a controller (11) which outputs control signals according to the monitoring signal; and a phase adjuster 9, Q1-Q4 which supplies drive current from the power supply to the motor coil in a specified number of phases according to the control signal. The motor is therefore started at high torque by energising 2 phase coils at a time and then switched to a lower torque by energising the coils one phase at a time once the motor speed has reached a specified value (eg half the target value). The coils may be energised two phases at a time for a time determined by a timer at the controller 11 after which they are energised one phase at a time. <IMAGE>

Description

SPINDLE MOTOR

BACKGROUND OF THE INVENTION

Field of the Invention

The invention relates to a spindle motor which may be used in, for example, a magnetic disk unit.

Prior Art

With the emergence of more compact magnetic disk units, more compact spindle motors have been needed. The system for obtaining a specified number of revolutions in these spindle motors is used in which several motor coils are excited one phase at a time. This system may be used in a spindle motor to drive disks in a magnetic disk unit.

Unfortunately, when a spindle motor is made compact, the torque of the spindle motor is reduced, and occasional incorrect revolution (or no revolution at all) is produced at start up when revolution force Is applied.

SUMMARY OF THE INVENTION

The purpose of this invention is to provide a spindle motor which reliably produces correct revolution at start-up. The spindle motor of this invention consists of a rotpr; magnetic disk disposed on the outer periphery of the rotor; multiphase motor coil supplying rotation power to the rotor following excitation by drive current; a power supply which supplies the drive current to the motor coil in phase; a rotation monitor which monitors the state of rotation of the 1 above rotor and outputs monitoring signals; a controller which outputs control signals according to the rotation monitoring signal; and a phase adjuster which supplies drive current from the power supply to the motor coil in a specified number of phases according to the control signals.

When the rotational-state monitor detects a state of rotation, it outputs a monitoring signal and then outputs a control signal from the controller.

The number of control-specified phases Is adjusted by the unit which supplies the drive current (supplied from the power supply) to the motor coil.

In this manner, the spindle motor of the present invention supplies the drive current to the motor coil in specified number of phases, depending on the state of rotation of the rotor.

For example, when the rotor starts. drive current is supplied to the twophase motor coil, and a large torque is generated to meet the requirement for the large load. Also, when the rotor attains a specified speed. the drive current can be supplied to the single phase motor coil to save power Thus, even if the size of the spindle motor is altered, improper revolution at start-up can be prevented.

In addition, the rotor of this spindle motor rapidly reaches the specified speed and thus reduces access time.

2 1 BRIEF DESCRI13TIONS OF THE DRAWINGS Fig. 1 shows a magnetic disk unit and the construction of the magnetic disk unit Including the spindle motor.

Fig. 2 is a circuit diagram which shows the circuit configuration of the spindle motor.

Fig. 3 is a circuit diagram which shows the circuit configuration of the spindle motor and the controller.

Fig. 4 is a functional block diagram which shows th controller of the spiridle motor.

Fig. 5 Is a vector diagram which shows the rotary torque at the rotor.

3 DETAILED DESCRIPTIONS OF THE PREFERRED EKBODIMENTS

The following is a description of embodiments of the present invention with reference to the drawings.

In Fig. 1, 1 is the spindle motor. This spindle motor 1 is within the main unit of the magnetic disk unit 2. The spindle motor I has the rotor la which is supported on a stator (not shown in figure) such that it can rotate freely. The rotor la has a magnet (not shown in the figure). The magnetic disk 3 is located on the outer periphery of the rotor la. The magnetic disk 3 rotates when the rotor la rotates.

Additionally, 4 indicates the head which writes data and subsequently reads it from the magnetic disk 3. This head 4 is mounted on the gimbal 5a at the tip of the carrier 5. A driving mechanism 6 with a voice coil motor is located on the rear part of the carrier 5. The carrier 5 moves the magnetic disk 3 in tlie direction of the radius by means of the driving mechanism 6.

Figs. 2 and 3 show the circuit configuration of the above spindle motor 1. As shown in Fig. 2, the spindle motor 1 is a unipolar-type, 4-phase spindle motor in which four motor coils Ll - L4 are connected.

Drive current is supplied to the Ll - L4 motor coils by the power supply (not shown in the figure) which is connected to terminals 7 and 8. Also, the phase adjuster 9, which turns the drive current supply on or off, is connected to the Ll - L4 motor coils. The phase adjuster 9 consists of the Q1 - Q4 FETs (Field Effect Transistors) as switching elements. The DI - D4 diodes are connected to the Ql - Q4 FETs to

4 1 1 prevent inverse current flow. Also, the capacitors C1 and C2 absorb power surges generated from the Ll - L4 motor coils; the C1 capacitor is connected to the Ll and L3 motor coils, and the C2 capacitor is connected to the L2 and L4 motor coils.

In Fig. 4, 10 is the rotation monitor. This rotation monitor 10 monitors the rotation state of the rotor la and outputs the KS1 monitoring signal. As this rotation monitor 10 monitors, a pulse signal detector, which detects pulse signals from the Ll - L4 motor coils, allows the rotor la to rotate. Also, as the rotation monitor 10 monitors, a detection scnsor which monitors the state of rotation and is based on servo sig.nzils, indicate the rotational angle written into the magnetic disk 3, can be used.

The symbol 11 indicates the controller. The controller 11 outputs the phase excited signal RSI and 2-phase excited signal RS2 to the drive 12 depending on the monitoring signal KS1 and allows the monitoring signal KS1 from the rotation monitor 10 to be input.

The drive 12 and FETs Ql - Q4 are connected by the control lines 13, 14, 15 and 16. The drive 12 outputs control current to the FETs Ql - Q4 by allowing the input of the 1-phase excitation signal RS1 or 2-phase excitation signal RS2 output from the controller 11.

The following describes the operation of the spindle motor 1 in the above config-uration:

(1) At start-up, the rotation monitor 10 senses that the rotor la of the spindle motor 1 has stopped and the rotation monitor 10 will then output the monitoring signal KS1.

i (2) When the monitoring signal KS1 is input to the controller 11, the controller 11 outputs the 2-phase excited signal RS2, depending on the monitoring signal KS1.

(3) When the 2-phase excited signal RS2 is input to the drive 12, control current Is supplied to the FETs Q1 and Q2 from the drive 12 through the control lines 13 and 14.

(4) The FETs Q1 and Q2 turn on when the control current is input. Then, the drive current supplied from the power supply flows into the motor coils Ll and L2 through the FETs Q1 and Q2, thus exciting the motor coils L1 and L2.

(5) After this, the control current is supplied to the FETs Q2 and Q3 from the drive 12 through the control lines 14 and 15. Then, the drive current flows to the motor coils L2 and L3 through the FETs Q2 and Q3, thus exciting the motor coils L2 and L3.

(6) Subsequently, the control current is supplied to the FETs Q3 and Q4 from the drive 12 through the control lines 15 and 16. Then, the drive current flows to the motor coils L3 and L4 through the FETs Q3 and Q4, thus exciting the motor coils L3 and L4.

(7) Subsequently, the control current is supplied to the FETs Q4 and Q1 from tile drive 12 through the control lines 16 and 1.3. Then, the drive current flows to the motor coils L4 and L1 through the FETs Q4 and Q1, and exciting the motor coils L4 and Ll.

(8) Steps (3) (7) are repeated.

6 p.

1 That Is, control signals are supplied to the FET Q1 Q4 in the order of Q1, Q2; Q2, Q3; Q3, Q4; Q4, Q1;... and the motor coils L1 - L4 are excited in the order of Ll, L2; L2, L3; L3, L4; L4, Ll;... Thus. the rotor la of the spindle motor generates a high torque prior to the Initiation of rotation.

(9) The controller 11 confirms that the rotor la speed has reached the specified speed (for example, approximately 1/2 the target speed, depending on the monitoring signal from the rotation monitor, and then outputs the 1-phase excitation signal RS1.

(10) When the 1-phase excitation signal RS1 is Input, the drive 12 supplies control current to the FETs Q1 - Q4 through the control lines 13 - 1G sequentially.

That is, the control signal is supplied to the FETs Q1 Q4 in the order of Q1, Q2, Q3, Q4, Ql...

(11) The FETs Q1, Q2, Q3 and Q4 are turned on and off sequentially. Drive current supplied from the power supply Is supplied to the motor coils Ll L4 in the order of L1, L2, L3, L4, L1,... Then, the motor coils Ll L4 are excited in the order of L1, L2, L3, L4, L1,... and the rotor la continues to rotate.

As Fig. 5 shows, the torque value of the rotor la. when the motor coils Ll - L4 are excited two phases at a time, becomes TV - T4' (approximately 1.4 times larger than the torque values T1 - T4 which are obtained by combining the 7 torque values T1 T4 of the rotor la when the motor coils L1 - L4 are excited one phase at a time.

When the above spindle motor 1 starts, the motor coils L1 - L4 are excited two phases at a time, the rotor la rotates and excites the motor coils Ll - L4 one phase at a time after the specified speed of the rotor la is reached.

That is, when the rotor la starts, it excites the motor coils L1 - L4 two phases at a time and achieves revolution at a high torque value. Also, the rotor la excites the motor coils Ll - L4 one phase at a time, and saves power during revolution.

In addition, the rotation monitor 10 can detect if the speed of the rotor la is 0 rpm. If this is true, the rotation monitor 10 will then output a monitoring signal.

Furthermore, the rotation monitor 10 can act as an acceleration sensor which detects the angular acceleration of the rotor la. If there is friction or adhesion (caused by, for example, solvents on the magnetic disk 3 surface) between the magnetic disk 3 and the head 4, the acceleration sensor detects that the negative angular acceleration exceeds a specified value. and then outputs a monitoring signal KS1 when the rotor la cannot be started, even if high load Is applied, and the motor coils L1 - L4 are excited, one phase at a time. Then, the controller 11 outputs the 2-phase excitation signal RS2 based on the monitoring signal KS1 and excites the motor coils L1 -L4, two phases at a time. Thus. the rotor la rotates at high torque and is therefore able to start.

In this manner, the motor coils Ll - L4 are excited, two 8 Z! 1 phases at a time and are thereby started at high torque, in the case where the motor coils LI - L4 cannot be started if the rotor la excites the motor coils Ll - L4 one phase at a time. Then, after the rotor la starts, the motor coils Ll L4 are excited one phase at a time, resulting in the rotation of the rotor la, thus enabling the rotor la to rotate without any improper revolution, and rotating the magnetic disk positively. Power consumption can thereby be further reduced.

The motor coils Ll - L4 may be excited one phase at a time, after a time lapse, by providing a time gauge as a timer at the controller 11 and exciting the motor coils Ll 1-4, two phases at a time, to rotate at a high torque value.

in this case, the controller 11 outputs the 2-phase excitation signal RS2 to the drive 12 at the starting of the rotor la. Based on this 2-phase excitation signal RS2, the drive 12' supplies control current to the FETs Q1 - Q4, two FETs at a time. Thus, as in the above embodiment, when starting the rotor la, the motor coils Ll - L4 are excited in sequence, two phases at a time, and the rotor la rotates at high torque. Then, the time gauge measures the time between the rotor la start and the output lapse signal which notifies the controller 11 of the interval. With this, the controller 11 outputs the 1-phase excitation signal RS1 to the drive 12 and control current is supplied sequentially to the FETs Q1 Q4 from the drive 12. Thus, the motor coils Ll - L4 are excited sequentially, one phase at a time, and the rotor la of the spindle motor 1 continues to rotate.

Although the motor coil Ll - L4 of the spindle motor 1 9 in the above embodiment is a 4-phase type, the number of motor coil phases is not limited to that in the above embodiment. - r

Claims

CLAIMS 1. A spindle motor comprising:

rotor; magnetic disk disposed on the outer periphery of the rotor; multiphase motor coil supplying rotation power to the rotor following excitation by drive current; power supply which supplies the drive current to the motor coil in phase; rotation monitor which monitors the state of rotation of the rotor and outputs monitoring signals; a controller which outputs control signals according to the monitoring signal; and a phase adjuster which supplies drive current from the power supply to the motor coil in -3 s-pecified number of phases according to the control signal.
2. A spindle motor according to claim 1, wherein said motor coil comprises 4 motor coils.
3. A spindle motor according to claim 1 c- 2, wherein said motor coil comprises a capacitor to absorb power surge.
4. A spindle motor according to any preceding claim wherein said rotation monitor comprises a detection sensor to detect revolution of the rotor.
5. A spindle motor according to claim 4, wherein said detection sensor outputs a monitoring signal when the revolution speed of the rotor is detected to have attained a specified value.

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6. A spindle motor according to claim 4 or 5, wherein said detection sensor outputs a monitoring signal when the revolution speed of the rotor is detected to be 0 revolutions per minute.
7. A spindle motor according to any preceding claim, wherein said rotation monitor comprises an acceleration sensor to measure the angular acceleration of the rotor.
8. A spindle motor according to any preceding claim, wherein said rotation monitor comprises a pulse signal detector to detect the pulse signal from the motor coil.
9. A spindle motor according to any preceding claim, wherein said magnetic disk has a servo signal.
10. A spindle motor according to claim 9, wherein said servo signal indicates the rotational angle.
11. A spindle motor according to claim 9 or 10, wherein said rotation monitor detects servo signals from the magnetic disk.
12. A spindle motor according to any preceding claim, wherein said controller comprises a control circuit for outputting control signals according to monitoring signals, and a driver to output control current according to the control signal.
13. A spindle motor according to any preceding claim, wherein said controller outputs a 2-phase excitation signal, according to the monitoring signal, to excite the motor coil two phases at a time at the initiation of rotor rotation.

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14. A spindle motor according to any preceding claim, wherein said phase- adjuster comprises an on/off switch for controlling the supply of drive current from the power supply unit to the motor coil.
15. A spindle motor according to claim 14, wherein said on/off switch comprises switching elements.
16. A spindle motor according to claim 15, wherein said switching elements comprise Field Effect Transistors.
17. A spindle motor according to claim 15 or 16, wherein said switching elements include a diode for preventing inverse current.
18. A spindle motor comprising: a rotor; a magnetic disk disposed on the outer periphery of the rotor; a multiphase motor coil supplying rotation power to the rotor following excitation by drive current; a power supply which sup -L plJes the drive current to the motor coil in phase; a tme gauge to output a lapse signal after a specified L-1, interval elapses following the initiation of rotation of the rotor; a controller to output a 2-phase excitation signal to excite the motor coil two phases at a time following no input of a lapse signal, and to output a 1-phase excitation signal to excite the motor coil one phase at a time following the input of a lapse signal; and 13 a phase-adjuster to supply drive current from the power supply to the 2- phase motor coil by the input of a 2-phase excitation signal, and said phase-adjuster to supply drive current from the power supply unit to the 1-phase motor coil by input of a 1-phase excitation signal.
19. A spindle motor according to claim 18, wherein said time-gauge comprises a timer.
20. A spindle motor substantially as herein described with reference to and as shown in the accompanying drawings.

14 Published 1991 at 7be Patent 0171ce. State House. 66/71 HighHolborn, LondonWClR47P- Further copies may be obtained frorn Sales Branch. Unit 6. Nimt Milc Point, Cwrnfelinfach. Cross Keys. Newport, NPI 7HZ. Printed by Multiplex techniques ltd, St Mary Cray. Kent-