U.S. patent application number 09/893549 was filed with the patent office on 2001-11-29 for semiconductor integrated circuit for brushless motor drive control and brushless motor dirve control apparatus.
This patent application is currently assigned to Hitachi, Ltd.. Invention is credited to Kawauchi, Kunihiro, Kokami, Yasuhiko, Seki, Kunio, Tsunoda, Toshiyuki.
Application Number | 20010045812 09/893549 |
Document ID | / |
Family ID | 18605700 |
Filed Date | 2001-11-29 |
United States Patent
Application |
20010045812 |
Kind Code |
A1 |
Seki, Kunio ; et
al. |
November 29, 2001 |
Semiconductor integrated circuit for brushless motor drive control
and brushless motor dirve control apparatus
Abstract
A pulse current having such a short duration as the rotor does
not react is passed through field coils of respective phases of a
brushless motor in first and second, mutually opposite, directions
sequentially, voltages induced, by the pulse currents in two
directions at each of the field coils of the non-conducting phase
are combined, the polarity of a combined voltage is detected, and a
field coil pair where a current is to be passed to start the motor
is determined based on the result of detection for each of field
coil of the non-conducting phase.
Inventors: |
Seki, Kunio; (Hinode,
JP) ; Tsunoda, Toshiyuki; (Maebashi, JP) ;
Kokami, Yasuhiko; (Takasaki, JP) ; Kawauchi,
Kunihiro; (Takasaki, JP) |
Correspondence
Address: |
MATTINGLY, STANGER & MALUR, P.C.
1800 DIAGONAL ROAD
SUITE 370
ALEXANDRIA
VA
22314
US
|
Assignee: |
Hitachi, Ltd.
|
Family ID: |
18605700 |
Appl. No.: |
09/893549 |
Filed: |
June 29, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
09893549 |
Jun 29, 2001 |
|
|
|
09818511 |
Mar 28, 2001 |
|
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Current U.S.
Class: |
318/727 |
Current CPC
Class: |
H02P 6/22 20130101 |
Class at
Publication: |
318/727 |
International
Class: |
H02P 001/24; H02P
001/42; H02P 003/18; H02P 005/28; H02P 007/36 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 29, 2000 |
JP |
2000-090037 |
Claims
What is claimed is:
1. A brushless motor drive control apparatus for rotating a
brushless motor by switching a current from one pair of field coils
to another pair of field coils of a polyphase brushless motor
having a plurality of field coils, comprising: a phase current
output circuit for generating a current to pass through the field
coils of respective phases of said motor; a phase switching control
circuit capable of controlling said phase current output circuit to
switch a current to pass from one pair of field coils to another
pair of field coils of said motor to achieve constant-speed
rotation and, when starting said motor, capable of controlling said
phase current output circuit to conduct a pulse current, having
such a duration as not to cause the rotor to react, to each of a
plurality of field coil pairs of said motor alternately in first
and second, mutually opposite, directions sequentially; an induced
voltage detecting circuit, connected to said phase current output
circuit, for detecting first and second voltages induced in field
coils of a non-conducting phase by said pulse current in said first
and second directions passed through each of said plurality of
field coil pairs; a combining circuit for generating a rotor
position signal by combining said first and second induced voltages
detected by said induced voltage detecting circuit at each of the
field coils of said non-conducting phase; a polarity detecting
circuit for generating a polarity signal representing a polarity of
a rotor position signal generated by said combining circuit at each
of the field coils of said non-conducting phase; and a memory
circuit for storing polarity data representing a plurality of
polarity signal generated by said polarity detecting circuit,
wherein a pair of field coils through which a current is to be
conducted to start the motor is determined on the basis of multiple
pieces of polarity data stored in said memory circuit, and wherein
said phase switching control circuit is arranged to control said
phase current output circuit to conduct a current through the field
coil pair determined.
2. A brushless motor drive control apparatus according to claim 1,
further comprising a discriminating circuit for determining a field
coil pair for current conduction to start said motor on the basis
of multiple pieces of polarity data stored in said memory circuit
and generating a phase selection setting signal to be supplied to
said phase switching control circuit.
3. A brushless motor drive control apparatus according to claim 2,
wherein said combining circuit includes a sample-and-hold circuit
for sampling and holding said first induced voltage and another
sample-and-hold circuit for sampling and holding said second
induced voltage, and an adder for adding together outputs of said
first and second sample-and-hold circuits.
4. A brushless motor drive control apparatus according to claim 2,
further comprising a timing circuit for, on the basis of a clock
signal, generating control signals to operate said phase switching
control circuit, said induced voltage detecting circuit, said
combining circuit, and said memory circuit at specified timing.
5. A brushless motor drive control apparatus according to claim 2,
further comprising a back e.m.f detecting circuit, connected to
said phase current output circuit, for detecting zero cross points
generated in the field coils of the non-conducting phase and
generating a phase switching timing signal, wherein said phase
switching control circuit switches a current from one field coil
pair to another according to said phase switching timing signal
from said back e.m.f. detecting circuit after the motor is started
and said phase current output circuit supplies the motor with a
current of a larger amplitude than that of said pulse current sent
to determine a field coil pair for current conduction to start the
motor.
6. A brushless motor drive control apparatus according to claim 1,
wherein said combining circuit includes a sample-and-hold circuit
for sampling and holding said first induced voltage and another
sample-and-hold circuit for sampling and holding said second
induced voltage, and an adder for adding together outputs of said
first and second sample-and-hold circuits.
7. A brushless motor drive control apparatus according to claim 1,
further comprising a timing circuit for, on the basis of a clock
signal, generating control signals to operate said phase switching
control circuit, said induced voltage detecting circuit, said
combining circuit, and said memory circuit at specified timing.
8. A brushless motor drive control apparatus according to claim 1,
further comprising a back e.m.f detecting circuit, connected to
said phase current output circuit, for detecting zero cross points
generated in the field coils of the non-conducting phase and
generating a phase switching timing signal, wherein said phase
switching control circuit switches a current from one field coil
pair to another according to said phase switching timing signal
from said back e.m.f. detecting circuit after the motor is started
and said phase current output circuit supplies the motor with a
current of a larger amplitude than that of said pulse current sent
to determine a field coil pair for current conduction to start the
motor.
9. A semiconductor integrated circuit for a drive control apparatus
of a polyphase brushless motor having a plurality of field coils,
comprising: a phase current output circuit for-generating a current
to pass through respective field coils of said motor; output
terminals for outputting a current to pass through field coils of
respective phases of said motor, said current being generated by
said phase current output circuit; a phase switching control
circuit capable of controlling said phase current output circuit to
switch a current to pass from one pair of field coils to another
pair of field coils of said motor for constant-speed rotation
thereof and, when starting said motor, capable of controlling said
phase current output circuit to conduct a pulse current, having
such a duration as not to cause the rotor to react, to each of a
plurality of field coil pairs of said motor alternately in first
and second, mutually opposite, directions sequentially; an induced
voltage detecting circuit, connected to said phase current output
circuit, for detecting first and second voltages induced in each of
said field coils of a non-conducting phase by said pulse current in
said two directions; an integrating circuit for generating a rotor
position signal by integrating said first induced voltage by said
pulse current in said first direction and then integrating said
second induced voltage by said pulse current in said second
direction at each of said field coils of the non-conducting phase;
a polarity detecting circuit for generating a polarity signal
representing a polarity of a rotor position signal generated by
said integrating circuit at each of said field coils of the
non-conducting phase; a memory circuit for storing polarity data
representing a plurality of polarity signal generated by said
polarity detecting circuit; and a discriminating circuit for
determining a field coil pair for current conduction to start said
motor on the basis of multiple pieces of polarity data stored in
said memory circuit and generating a phase selection setting signal
to be supplied to said phase switching control circuit, each of
said circuits and said output terminals being formed on a single
semiconductor chip.
10. A semiconductor integrated circuit according to claim 9,
wherein said integrating circuit includes a capacitor element
connected as an externally-mounted element to an external terminal
provided on said semiconductor chip.
11. A semiconductor integrated circuit according to claim 9,
further comprising a timing circuit, mounted on said semiconductor
chip, for generating control signals on the basis of a clock signal
for operating said phase switching control circuit, said induced
voltage detecting circuit, said integrating circuit, said memory
circuit and said discriminating circuit respectively at
predetermined timing.
12. A semiconductor integrated circuit according to claim 9,
further comprising a back e.m.f detecting circuit, mounted on said
semiconductor chip and connected to said phase current output
circuit, for detecting zero cross points generated in the field
coils of the non-conducting phase and generating a phase switching
timing signal, wherein said phase switching control circuit
switches a current from one field coil pair to another according to
said phase switching timing signal from said back e.m.f. detecting
circuit after the motor is started and said phase current output
circuit supplies the motor with a current of a larger amplitude
than that of said pulse current sent to determine a field coil pair
for current conduction to start the motor.
13. A method for starting a polyphase brushless motor having a
rotor containing a magnet and a stator containing a plurality of
field coils, comprising the steps of: passing a pulse current,
having such a duration as the rotor does not react, through each
pair of field coils in first and second, mutually opposite,
directions sequentially, each pair being formed by a field coil and
one of the other field coils of said motor; generating first and
second induced voltage signals by detecting voltages induced in
each field coil of a non-conducting phase by a pulse current
applied in said first and second directions; combining said first
and second voltages at each field coil of the non-conducting phase
to generate a plurality of rotor position signal representing the
relative position of said rotor with respect to said stator;
detecting polarities of said plurality of rotor position signal;
and determining a field coil pair of the phases for current
conduction to start said motor using detection results of
polarities of said plurality of rotor position signal.
14. A motor starting method according to claim 13, wherein said
rotor position signal is generated by adding up said first and
second induced voltage signals.
15. A motor starting method according to claim 13, wherein said
rotor position signal is generated by integrating said first
induced voltage signal and, under the condition that the result of
said integration is maintained, integrating second induced voltage
signal.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to a technique for drive
control of a brushless motor and a technique effective when applied
to a method for determining phases (a pair of phases) at which to
start current conduction when starting the motor, and particularly
concerns a technique effective when used in a drive control
apparatus of a spindle motor for rotating a disk-type storage
medium, such as a HDD (hard disk drive) device.
[0002] With hard disk devices, there has been a strong demand for
higher speed in writing and reading information on a magnetic disk,
namely, quicker access speed. To this end, it is required that the
spindle motor be made much faster. In addition, demand is also
mounting for reductions in size, power consumption and production
cost of the drive control apparatuses. In conventional hard disk
devices, DC polyphase brushless motors are generally used for their
spindle motor to rotate the magnetic disks at high speed, and
information is written or read on the rotating magnetic disk by
bringing the read/write magnetic heads into contact with or in
close vicinity to the disk.
[0003] In brushless motors, there has been used a motor drive
control method by which to prevent reverse rotation of the motor by
detecting the positional relation of the rotor and the stator by
means of Hall elements and by, from the detected positional
relation, determining field-coil phases at which current conduction
is to be started. Because mounting a rotor position detector using
Hall elements in the motor increases the difficulty of downsizing
the motor, sensorless motors have come to be used in large numbers
in the hard disk devices. However, if the magnetic disk is driven
by a sensorless motor, the rotor is likely to make a reverse
rotation for an instant with a probability of 1/2 when the disk
starts to rotate.
[0004] With the rapidly multiplying storage density of the magnetic
disks in hard disk devices in recent years, the magnetic read/write
heads have been sharply reduced in size. Consequently, in the hard
disk devices with the magnetic heads miniaturized to such an
extent, there is a problem that if the rotor is turned in reverse
even for an instant, the magnetic heads may suffer a fatal damage.
To solve this problem, a control method has been proposed in which
a pulse current of so short a duration as not to cause the rotor to
react is supplied to the field coils of the stator, and the field
coils where the amplitude is at the maximum value, in other words,
the phases, where the field of the rotor magnet in the same
direction as the generated field of the coils, causing
magnetization to be saturated to make current flow most easily, are
determined as the phases at which to start current conduction
(Refer to JP-A-63-694895 published on Mar. 29, 1988 which
corresponds to U.S. Ser. No. 880754 filed on Jul. 1, 1986).
[0005] Another control method has been proposed in which a pulse
current is conducted through the field coils of the stator and then
the pulse current is conducted in the opposite direction, and
differences in current rise time constant are detected at
respective field coils where the current is passed through, and
according to detection results, the position of the rotor is
determined to determine a pair of phases at which current
conduction is started. In other words, this control method is such
that phases at which current conduction is started are determined
by determining the rotor position based on detection results
obtained by detection of differences in inductance by making use of
a phenomenon that the inductance of the field coils varies whether
the direction of the magnetic field is the same or not between the
field coils and the rotor magnet (that is to say, whether magnetic
saturation occurs or not) (Refer to JP-A-3-207250 published on Sep.
10, 1991 which corresponds to U.S. Ser. No. 413311 filed on Sep.
27, 1989).
[0006] In addition to the above inventions, another invention has
been proposed that the stopped position of the rotor is determined
by applying a diagnosis signal of a frequency higher than the
frequency of an exciting signal applied when the motor is started,
to a single coil or two or more coils connected in series and
detecting an induced voltage of one of the serially-connected coils
(Refer to JP-A-7-274585 published on Oct. 20, 1995).
SUMMARY OF THE INVENTION
[0007] However, the present inventors have revealed that the prior
art described above suffer problems as follows.
[0008] In the control method that determines a pair of phases,
where current conduction is started, by passing a pulse current and
detecting the maximum amplitude value, the maximum amplitude value
depends on variations in winding in the field coils of the stator,
for which reason detection errors occur due to very small winding
variations that are unavoidable in the manufacturing process. In
the control method that determines a pair of phases, where current
conduction is started, by detecting the rotor position based on
differences in current rise time constant, because a phenomenon of
magnetic saturation is used, differences in time constant do not
become conspicuous unless a fairly large current is passed, and
therefore it is difficult to detect differences in the time
constant when a current passed is so small as the rotor does not
react to it. Another problem with this control method is that the
point of reversal of the large-small relation among the time
constants that occurs when the direction of a current is reversed
does not coincide with the point of magnetic saturation, resulting
in errors in determination results.
[0009] The present invention has as its object to provide a
brushless motor drive control technique that can prevents reverse
rotation of the motor at starting by detecting the position of the
rotor relative to the stator with fewer errors and determining a
field coil pair at which current conduction is started.
[0010] According to an aspect of the present invention, a pair of
phases for current conduction to start the motor is determined by
passing a pulse current with a duration so short as the rotor does
not react through the field coil of any phase of the motor in first
and second, mutually opposite, directions sequentially, and
detecting induced voltages in the non-conducting phase by a pulse
current in two opposite directions, combining voltages induced by a
pulse current in the first direction and a pulse current in the
second direction, detecting the polarities of combination results,
and determining a pair of phases for current conduction when
starting the motor based on polarity detection results related to a
plurality of the conducting phases.
[0011] The above-mentioned and other objects and features of the
present invention will become obvious from the following
description of this specification and the accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIGS. 1a and 1b are schematic diagrams illustrating the
principle of a rotor position detecting method according to one
embodiment of the present invention, in each of which diagrams the
rotor is at a standstill with the border between an S pole and an N
pole of the magnet of the rotor coincident with the center of the
field coil Lv of the stator;
[0013] FIGS. 2a and 2b are schematic diagrams illustrating the
principle of a rotor position detecting method according to one
embodiment of the present invention, in each of which diagrams the
rotor is at a standstill with the border between an S pole and an N
pole of the magnet of the rotor shifted a little from the center of
the field coil Lv to the field coil Lw of the stator.
[0014] FIGS. 3a and 3b are schematic diagrams illustrating the
principle of a rotor position detecting method according to one
embodiment of the present invention, in each of which diagrams the
rotor is at a standstill with the border between an S pole and an N
pole of the magnet of the rotor shifted a little from the center of
the field coil Lv to the field coil Lu of the stator;
[0015] FIGS. 4a and 4b are graphs showing the relation between the
position of the rotor relative to the stator and induced voltages
at the non-conducting phases, obtained by an experiment conducted
by the present inventors;
[0016] FIG. 5 is a waveform diagram with respect to a three-phase
motor, showing a relation between detection results on the positive
and negative polarities of induced voltages Eu, Ev and Ew detected
at the field coils Lu, Lv and Lw and leakage fluxes to the
non-conducting phases, and showing a relation between leakage
fluxes to the non-conducting phases and torques (back electromotive
forces) of the respective field coils Lu, Lv and Lw when the motor
is rotating;
[0017] FIG. 6 is a block diagram of brushless motor drive control
apparatus according to one embodiment of the present invention in a
motor driver unit used in a hard disk storage device;
[0018] FIG. 7 is a block diagram of a brushless motor drive control
apparatus according to one embodiment of the present invention in a
motor driver unit used in a hard disk storage device;
[0019] FIG. 8 is a flowchart showing the operation procedure of the
apparatus in FIG. 7;
[0020] FIG. 9 is a timing chart showing the operation of the
apparatus in FIG. 7 determining the rotor position by conducting a
pulse current through the field coils of respective phases and
detecting induced voltages at the non-conducting phases according
to the procedure shown in FIG. 8;
[0021] FIG. 10 is a block diagram for explaining the motor driver
unit, which is used in a hard disk storage device and which
includes the brushless motor drive control apparatus according to
one embodiment of the present invention;
[0022] FIG. 11 is a flowchart showing a control procedure from
starting the motor till a constant speed operation in a motor
driver unit including the brushless motor drive control apparatus
according to one embodiment of the present invention; and
[0023] FIG. 12 is a block diagram showing a representative
configuration of the hard disk device as an example of a system
using the motor driver unit including the brushless motor drive
control apparatus according to one embodiment of the present
invention.
DESCRIPTION OF THE EMBODIMENTS
[0024] Embodiments will be described with reference to the
accompanying drawings.
[0025] Before proceeding with the description of the embodiments of
the present invention, explanation will be made of the principle of
rotor position detection, on which those embodiments are based, by
referring to FIGS. 1a, 1b, 2a, 2b, 3a and 3b. These figures
schematically illustrate the relation of any three field coils Lu,
Lv and Lw representing 3.times.n (n is a positive integer) coils
with respect to the rotor magnet in order to explain the positional
relation of the field coils of the stator with respect to the rotor
magnet MG in a three-phase type polyphase brushless motor. The PIO
denotes a phase current output circuit to pass currents through the
field coils Lu, Lv and Lw. This phase current output circuit
outputs a total of six currents (including currents in mutually
opposite directions) to conduct them through any pair of field
coils according to a specified sequence to thereby rotate the
rotor. In FIGS. 1a, 1b, 2a, 2b, 3a and 3b, the rotor magnet MG and
the stator field coils Lu, Lv and Lw are arranged linearly but they
are arranged coaxially in a real motor.
[0026] FIG. 1a shows that the rotor is at a standstill with the
border between an S pole and an N pole of the magnet MG of the
rotor coincident with the center of the field coil Lv of the
stator. Under this condition, when a short pulse current Iw is
supplied from a phase current output terminal W, to which the field
coil Lw is connected, to a phase current output terminal U, to
which the field coil Lu is connected, the magnetic lines DMu
produced by the field coil Lu are almost in the same direction as
the magnetic lines DMr1 from the N pole of the magnet MG of the
rotor facing the field coil Lu and, moreover, the magnetic lines
DMw produced by the field coil Lw are almost in the same direction
as the magnetic lines DMr2 of the S pole of the magnet MG of the
rotor facing the field coil Lw. However, the magnetic lines DMu of
the field coil Lu is in a direction opposite to the direction of
the magnetic lines DMw of the field coil Lw. Because the border
between the S pole and the N pole of the magnet MG coincides with
the center of the field coil Lv of the stator, the leakage flux
from the field coil Lu to the field coil Lv is the same in
magnitude with and opposite in direction from the leakage flux from
the field coil Lw to the field coil Lv and therefore they cancel
each other, so that the induced voltage in the field coil Lv is
zero.
[0027] Under this condition, to pass a current through the field
coils Lu and Lw in reverse direction, a short pulse current Iu is
supplied from the phase current output terminal U to the phase
current output terminal W as shown in FIG. 1b, the magnetic lines
produced by the field coils Lu and Lw are respectively opposite in
direction to the magnetic lines emerging from the N poles and going
into the S poles of the magnet MG of the rotor which respectively
face the field coils Lu and Lw. Therefore, the flux densities in
the field coils Lu and Lw are lower than in FIG. 1a, and the
leakage fluxes from the field coils Lu and Lw to the field coil Lv
are small but are the same in magnitude and opposite in direction
as in FIG. 1a, so that they cancel each other and the induced
voltage in the field coil Lv is zero.
[0028] Description will now be made of the state that the rotor is
at a standstill with the border of an S pole and an N pole of the
magnet MG of the rotor being located a little shifted from the
center of the field coil Lv to the field coil Lw as in FIG. 2a.
Under this condition, because the N pole of the magnet MG squarely
faces the front side of the field coil Lu, the density of the flux
emerging from that portion of the magnet MG of the rotor which
faces the field coil Lu and then passing through the field coil Lu
is higher than the density of the flux emerging from that portion
of the rotor magnet MG which faces the field coil Lw and then
passing through the field coil Lw. Therefore, if a short pulse
current Iu is supplied from the phase current output terminal W to
the phase current output terminal U, the magnetic lines DMu
produced by the field coil Lu is in the same direction as the
above-mentioned flux (magnetic lines) emerging from that portion of
the rotor magnet MG which faces the field coil Lu and then passing
through the field coil Lu, and the magnetic lines DMw produced by
the field coil Lw is also in the same direction as the
above-mentioned flux (magnetic lines) emerging from that portion of
the rotor magnet MG which faces the field coil Lw and then passing
through the field coil Lw. However, due to the above-mentioned
difference in flux density, the leakage flux ML1 from the field
coil Lu to the field coil Lv is larger than the leakage flux ML2
from the field coil Lw to the field coil Lv, so that a voltage is
induced in the field coil according to the difference in leakage
flux.
[0029] On the other hand, as in FIG. 2a, under the condition that
the rotor is at a standstill with the border between an S pole and
an N pole of the rotor magnet MG being shifted a little from the
center of the field coil Lv to the field coil Lw of the stator, the
direction in which the current is supplied is reversed, and a short
pulse current Iu is conducted from the phase current output
terminal U to the phase current output terminal W as shown in FIG.
2b. Though the density of the flux emerging from the rotor magnet
MG and then passing through the field coil Lu and the density of
the flux emerging from the rotor magnet MG and then passing through
the field coil Lw are the same as in FIG. 2a, the directions of the
magnetic lines produced by the field coils Lu and Lw are opposite
to the directions of the magnetic lines emerging from the N poles
and going into the S poles of the magnet MG of the rotor that
respectively face the field coils. In addition, the magnetic lines
of the field coil Lu are set off by the N pole of the rotor magnet
MG to a greater extent than the magnetic lines of the field coil Lw
are set off by the S pole. Therefore, the leakage flux ML1 from the
field coil Lu to the field coil Lv is smaller than the leakage flux
ML2 from the field coil Lw to the field coil Lv, but because the
directions of the leakage fluxes ML1 and LM2 are reverse from those
in FIG. 2a, the polarity of the voltage induced in the Lv by the
difference in leakage flux is the same as in FIG. 2a.
[0030] Moreover, in the above case, the voltage induced in the
field coil Lv is greater when a current is sent such that the
magnetic lines produced by the field coils Lu and Lv are in the
same direction as the magnetic lines of the rotor magnet MG as in
FIG. 2a than when a current is sent such that the magnetic lines
produced by the field coils Lu and Lv are in the opposite direction
to the direction of the magnetic lines of the rotor magnet MG.
Therefore, by passing a current through the field coils Lu and Lw
alternately in opposite directions, detecting and comparing the
voltage induced in the field coil Lv, it is possible to determine
which poles are close to which field coils and whether the poles
are north or south.
[0031] FIG. 3a shows the state that the rotor is at a standstill
with the border between an S pole and an N pole of the magnet MG of
the rotor being shifted a little away from the center of the field
coil Lv of the stator to the field coil Lu. Under this condition,
because the S pole of the rotor magnet MG squarely faces the front
side of the field coil Lw, the density of the flux emerging from
that portion of the rotor magnet MG which faces the field coil Lw
and then passing through the field coil Lw is higher than the
density of the flux emerging from that portion of the rotor magnet
MG which faces the field coil Lu and passing through the field coil
Lu. Therefore, when a short pulse current Iw is supplied from the
phase current output terminal W to the phase current output
terminal U, the magnetic lines DMw produced by field coil Lw are in
the same direction as the above-mentioned flux (magnetic lines)
emerging from that portion of the rotor magnet MG which faces the
field coil Lw and passing through the field coil Lw and also the
magnetic lines DMu produced by the field coil Lu are in the same
direction as the above-mentioned flux (magnetic lines) emerging
from that portion of the rotor magnet MG which faces the field coil
Lu and passing through the field coil Lu. However, owing to the
above-mentioned difference in flux density, the leakage flux ML2
from the field coil Lw to the field coil Lv is larger than the flux
ML1 from the field coil Lu to the field coil Lv and the voltage is
induced in the field coil Lv according to the difference in leakage
flux. The voltage induced in the field coil Lv in FIG. 3a is
opposite in polarity to the voltage induced in the field coil Lv in
FIGS. 2a and 2b.
[0032] When the direction of current flow is reversed and a short
pulse current is conducted from the phase current output terminal U
to the phase current output terminal W as shown in FIG. 3b, the
density of the flux emerging from the rotor magnet MG and passing
through the field coil Lw is the same as the density of the flux
emerging from the rotor magnet MG and passing through the field
coil Lu as in FIG. 3a, but the magnetic lines produced by the field
coils Lw and Lu are respectively opposite in direction to the
magnetic lines from the S and the N poles of the rotor magnet MG
facing those field coils. Moreover, the magnetic lines produced by
the field coil Lw are set off by the S pole of the rotor magnet MG
to a greater extent than the magnetic lines produced by the field
coil Lu are set off by the N pole of the rotor magnet MG.
Therefore, though the leakage flux ML2 from the field coil Lw to
the field coil Lv is smaller than the leakage flux ML1 from the
field coil Lu to the field coil Lv, because the direction of the
magnetic lines ML1 and ML2 is opposite to that in FIG. 3a, the
polarity of the voltage induced in the field coil Lv according to
the difference in leakage flux is the same as in FIG. 3a.
[0033] In addition, the voltage induced in the field coil Lv is
larger when a current is supplied such that the magnetic lines
produced are in the same direction as the magnetic lines of the
rotor magnet MG as shown in FIG. 3a as in FIGS. 2a and 2b than when
a current is supplied such that the magnetic lines produced by the
field coils Lu and Lv are respectively opposite in direction to the
magnetic lines of the rotor magnet MG as shown in FIG. 3b.
Therefore, also in this case, by passing a current through the
field coils Lu and Lw alternately in opposite directions, detecting
and comparing the voltage induced in the field coil Lv, it is
possible to determine which poles are close to which field coils
and whether the poles are north or south. Note that the polarity of
the greater one of the leakage fluxes detected is opposite to that
detected in the case of FIG. 2.
[0034] FIG. 4a shows a result of a test conducted by the inventors.
The vertical axis indicates the detected values of the induced
voltage and the horizontal axis indicates the position of the rotor
with respect to the stator expressed in electrical angles. For
example, in a motor with a 12-pole rotor, a mechanical angle of 60
degrees corresponds to an electrical angle of 360 degrees. In other
words, FIG. 4a shows the result of measurement of voltages induced
in the field coil Lv by passing a current through the field coils
Lu and Lw alternately in opposite directions.
[0035] In FIG. 4a, the solid line A indicates the induced voltage
in the field coil Lv when a current is conducted from the field
coil Lw to the field coil Lu and the broken line B indicates the
induced voltage in the field coil Lv when a current is conducted
from the field coil Lu to the field coil Lw. From FIG. 4a, one of
the zero-cross points of the two curves (A and B) is not clear, in
other words, it is difficult to uniquely determine the positional
relation between the rotor and the stator from induced voltages
detected when a current was sent in one direction. Therefore, if an
attempt is made to determine the rotor position from induced
voltages by a current supplied in one direction, errors are likely
to occur. So, the inventors combined (add up) the above two curves
by way of trial, and found as indicated by the broken line C in
FIG. 4b that the zero-cross points became clear and the rotor
position can be determined with high accuracy.
[0036] According to an aspect of the present invention, the present
invention is based on an idea of providing the brushless motor
drive circuit with a circuit for determining a pair of phases at
which current conduction is started by conducting a pulse current
through two field coils alternately in opposite directions,
combining (adding) the voltages induced in the non-conducting-phase
field coil by respective currents and sampled and held by a
sample-and-hold circuit, or integrating and then adding up the
respective induced voltages, and on the basis of the sum, detecting
the polarities of the induced voltages.
[0037] FIG. 5 shows with regard to a three-phase motor the relation
between detected polarities (positive and negative) of the induced
voltages Eu, Ev and Ew detected at the field coils Lu, Lv and Lw
and the leakage fluxes .phi.u, .phi.v and .phi.w to the
non-conducting-phase field coils, and the relation between the
leakage fluxes .phi.u, .phi.v and .phi.w to the
non-conducting-phase field coils and the torque Tu, Tv and Tw,
namely, the back electromotive forces of the field coils Lu, Lv and
Lw while the motor was at a standstill.
[0038] If the polarity-detecting results for the detected induced
voltages Eu, Ev and Ew when the motor is at a standstill are "+, +,
-" for example, by conducting a current from the u-phase field coil
Lu to the v-phase field coil Lv to start the motor, the maximum
torque can be obtained. It is understood from FIG. 5 that the
positions where the polarities of the induced voltages are inverted
coincide with the positions where the polarities of the leakage
fluxes are inverted and it never occurs that detection about the
polarity of induced voltages is unclear. Moreover, because the
leakage flux is proportional to the flux density in the field coil,
it is not always required to make magnetic saturation occur in the
field coil when detecting an induced voltage. Therefore, it is
possible to make this determination by passing a smaller pulse
current as compared with one of the conventional control methods in
which a determination is made on a pair of phases at which to start
current conduction by detecting the rotor position based on
differences in current rise time constant.
[0039] Table 1 shows the relation between the polarity detection
results for the combined induced voltages Eu, Ev and Ew and the
phases for starting current conduction. Obviously, the relation in
Table 1 corresponds to the relation shown in FIG. 5. After the
polarity detection result is obtained, by arranging for a
determination to be made on a pair of phases at which to start
current conduction with reference to Table 1, the motor can be
started in the correct rotating direction in a shortest time
regardless of the rotor position at the moment. The polarity
(positive or negative) detection results of the induced voltages
Eu, Ev and Ew can never be all "+" or all "-" when induced voltages
are detected normally at the field coils of the respective phases.
Therefore, if such detection results are given, this should be
regarded as caused by detection errors and detection should be
carried out over again.
1 TABLE 1 START CURRENT CONDUCTION PHASES INDUCED VOLTAGE
(DIRECTION OF EU Ev EW CURRENT FLOW) DETECTION negative negative
positive phase v .fwdarw. phase u RESULT positive negative positive
phase w .fwdarw. phase u positive negative negative phase w
.fwdarw. phase v positive positive negative phase u .fwdarw. phase
v negative positive negative phase u .fwdarw. phase w negative
positive positive phase v .fwdarw. phase w
[0040] Meanwhile, in a real motor, even if the rotor and the stator
are in the positional relation shown in FIGS. 1a and 1b, in other
words, even if the center of the field coil Lv coincides with the
border between an S pole and an N pole of the rotor, when a current
is passed through the field coils Lu and Lw, the leakage flux from
either one of those field coils to the field coil Lv is greater
than the leakage flux from the other coil due to, for example,
variation in winding of the coils, and a voltage proportional to a
difference in leakage flux is induced in the field coil Lv.
However, in FIG. 1a, a current is supplied such that the magnetic
lines of the field coils are in the same direction as the magnetic
lines of the rotor magnet, whereas, in FIG. 1b, a current is
supplies such that the magnetic lines of the field coils are in the
opposite direction to the magnetic lines of the rotor magnet.
Therefore, in these two cases, the voltages induced in the field
coil Lv ascribable to variation in winding are mutually opposite in
polarity, and when these induced voltages are added together, they
cancel each other and become zero.
[0041] FIG. 6 shows a brushless motor drive control apparatus
mounted in a motor driver unit for use in a hard disk device and
structured according to one embodiment of the present
invention.
[0042] In FIG. 6, reference numeral 11 denotes a phase current
output circuit that supplies current to the field coils Lu, Lv and
Lw in a three-phase brushless motor, 12 denotes a phase switching
control circuit that supplies a selection signal of the phases,
through which a current is to be passed, to the phase current
output circuit 11, 13 denotes an induced voltage detecting circuit,
connected to the output terminals U, V and W of the phase current
output circuit 11, for detecting induced voltages, 14a and 14b
denote sample-and-hold circuits for sampling and holding the
induced voltages detected by the induced voltage output circuit 13
when the field coils are supplied with a current in two opposite
directions, and 15 denotes an adder circuit that adds up the
voltages held in the sample-and-hold circuits 14a and 14b and
generates a rotor position signal.
[0043] Reference numeral 16 denotes a polarity detecting circuit
for detecting the polarity of an addition result in the adder
circuit 15, in other words, detecting whether the sum of voltages
is positive or negative, and generating a polarity signal, 17a, 17b
and 17c denote data latch circuits for storing polarity data
representing polarity signals generated by the polarity detecting
circuit 16 when a current is passed through the field coils, 18
denotes a discriminating circuit for determining rotor position, in
other words, a pair of phases through which a current is to be
supplied in the first place based on polarity data stored in the
data latch circuits 17a, 17b and 17c, from the relation in Table 1,
for example, and generating a phase selection setting signal, 19
denotes a timing circuit that generates control signals based on a
clock signal CLK, and outputs to the circuit blocks 11 to 18.
[0044] The timing circuit 19 supplies a phase selection switching
timing signal T.CLK and a rotor position detection ON/OFF signal
STR to the phase switching control circuit 12, an ON/OFF signal SNS
to the induced voltage detecting circuit 13, a sampling timing
signal SPR to the sample-and-hold circuits 14a and 14b, an
operation timing signal ADD and a reset signal RST to the adder
circuit 15, latch timing signals LTA to LTC to the data latch
circuits 17a, 17b and 17c, a determination timing signal JDG to the
discriminating circuit 18. The circuit blocks 11 to 18 operate
sequentially by control signals from the timing circuit 19.
[0045] By provision of this timing circuit 19, it becomes possible
to realize a drive control apparatus which can start a brushless
motor in a short time by determining by itself a pair of phases at
which to start current conduction when a clock signal is only given
without control signals being generated and supplied
externally.
[0046] When the ON/OFF signal STR issued from the timing circuit 19
is at its effective level, the phase switching control circuit 12
sends a phase selection control signal to the phase current output
circuit 11 to detect the rotor position and pass a small-pulse
current through the field coils. In response to the phase selection
control signal from the phase-switching control circuit 12, the
phase current output circuit 11 sends a pulse current, having such
a short duration as the rotor does not react, to any pair of field
coils Lu, Lv and Lw in one direction or in the opposite direction.
On the other hand, when the phase switching control circuit 12
receives a phase selection setting signal COMMST indicating the
phases at which to start current conduction, from the
discriminating circuit 18, the phase switching control circuit 12
sends a phase selection control signal to the phase current output
circuit 11 directing it to pass a pulse current through the set
phases at which to start current conduction to rotate the motor. At
this time, the ON/OFF signal STR from the timing circuit 19 is at
the effective level.
[0047] The induced voltage detecting circuit 13 has a rotor
position detecting action ON/OFF signal SNS supplied from the
timing circuit 19 and also has another signal, indicating which
phases are being selected, supplied from the phase switching
control circuit 12. By those signals, the induced voltage detecting
circuit 13 detects and amplifies the voltage induced in the
non-conducting-phase coil. The induced voltage detecting circuit
13, if formed by a MOSFET, may include a switch (selector) to
select a voltage of the non-conducting phase, where current is not
flowing, out of the output terminals U, V and W of the phase
current output circuit 11 and also an amplifier circuit to amplify
the selected voltage. If formed by a bipolar transistor, the
induced voltage detecting circuit 13 may include three differential
amplifiers that each have at one input terminal supplied with one
of the voltages of the output terminals U, V and W of the phase
current output circuit 11 and at the other input terminal supplied
with the potential at the common connection node NO of the
respective field coils. When the induced voltage detecting circuit
13 is formed by three differential amplifier circuits, the circuit
13 may be configured such that any one of the differential
amplifier circuits performs amplification when its current source
is turned on by a phase selection control signal.
[0048] The adder circuit 15 may be an analog adder circuit using an
operational amplifier or may be a digital adder circuit. In the
case of a digital adder, it is only necessary to insert an A/D
converter circuit as the stage subsequent to the sample-and-hold
circuits 14a and 14b. The polarity detecting circuit 16 may be an
analog or digital circuit depending on the type of the adder
circuit 15. If the adder 15 is formed as a digital circuit, the
polarity detecting circuit 16 may be formed by a subtractor. In
place of the sample-and-hold circuits 14a and 14b, registers may be
used, and an A/D converter circuit may be provided at the preceding
stage to have the detected induced voltage converted into a digital
value and stored as digital data in the registers.
[0049] In the above embodiment, the discriminating circuit 18 that
designates start current conduction phases from a polarity
detection result is mounted together with the induced voltage
detecting circuit 13, etc. However, it is possible to provide a
microcomputer that receives polarity data from the latch circuits
17a to 17c, which hold data from the polarity detecting circuit 16,
and determines a pair of phases at which to start current
conduction and sets the phase data in the phase switching control
circuit 12.
[0050] FIG. 7 shows a motor drive control apparatus in a motor
driver unit, which is used in a hard disk storage device and which
is structured according to another embodiment of the present
invention.
[0051] This embodiment uses an integrating circuit 20, which has
replaced the sample-and-hold circuits 14a and 14b and the adder 15
in the embodiment shown in FIG. 6. This integrating circuit 20 may
be formed by a well-known integrating circuit including a CR
integrating circuit made of a capacitor and a resistance, or by a
well-known integrating circuit including an operational amplifier
and a capacitor connected between an output terminal and an
inverted input terminal of the amplifier.
[0052] In this embodiment, by a control signal from the timing
circuit 19, the integrating circuit integrates an induced voltage
which is detected at the non-conducting phase by the induced
voltage detecting circuit 13 when a pulse current is passed through
the field coils in one direction in the first place and, under the
condition that the result of integration is maintained, also
integrates an induced voltage which is detected at the
non-conducting phase by the induced voltage detecting circuit 13
when a pulse current is passed through the field coils in the
opposite direction. The polarity detecting circuit 16 is used to
detect the polarity of the electric charge remaining in the
capacitor as a component part of the integrating circuit (hereafter
referred to as an integrating capacitor). After this determination
is made, control is performed so that the integrating capacitor is
reset once, and then a pulse current is passed through a subsequent
pair of field coils, and the induced voltage detected is
integrated.
[0053] Description will be made of the operation of the motor drive
control apparatus in FIG. 7 with reference to a flowchart in FIG.
8. FIG. 8 shows the operation procedures of the phase current
output circuit 11 at left and the induced current detecting circuit
13 and the integrating circuit 20 at right to show the related
actions compared with each other.
[0054] When the enable signal EN (Refer to FIGS. 9 and 10) from a
control circuit is asserted to the low level, the timing circuit 19
starts to generate a control signal for detecting the rotor
position. With this action got started, in the first step S0, while
the output terminals of the phase current output circuit 11 are in
high impedance state in which the terminals are all opened, that
is, no current is output from any phase output terminal, the
capacitor of the integrating circuit 20 is reset, more simply, the
capacitor discharges itself of electric charge. Next, a pulse
current is passed from the phase v to the phase w by the phase
current output circuit 11. The pulse current used has so short a
duration as the rotor does not react to it. The induced voltage of
the phase u, which is non-conducting at this moment, is detected by
the detecting circuit 13, and is integrated by the integrating
circuit 20 (Step S1).
[0055] Subsequently, in a step S2, all phase terminals of the phase
current output circuit 11 are opened, and for this while the
voltage integrated in the integrating circuit 20 is held. In the
next step S3, the phase current output circuit 11 sends a pulse
current from the phase w to the phase v in the opposite direction
to the current flow in the step S1. At this time, the induced
voltage of the phase u in the non-conducting state is detected by
the induced voltage detecting circuit 13, and the phase-u induced
voltage is integrated using the result of the previous integration
as the initial value. Accordingly, in the integrating capacitor,
the integration result of the phase-u induced voltage when a
current was passed from the phase v to the phase w is added with
the integration result of the phase-u induced voltage when a
current was passed from the phase w to the phase v.
[0056] In the step S4, the polarity of the electric charge
remaining in the integrating capacitor is detected by the polarity
detecting circuit 16, and a detection decision result u-DATA is
stored in the first circuit 17a. All the output terminals of the
phase current output circuit 11 are opened, and in the integrating
circuit 20, the electric charge held in the integrating capacitor
is reset. In a step S5, the phase current output circuit 11 passes
a pulse current from the phase w to the phase u. At this time, the
induced voltage of the phase v, which is not conducting, is
detected by the detecting circuit 13, and the induced voltage is
integrated by the integrating circuit 20.
[0057] In a step S6, the voltage integrated by the integrating
circuit 20 is held, and all output terminals of the phase current
output circuit 11 are opened. In the next step S7, the phase
current output circuit 11 passes a pulse current from the phase u
to the w phase in the direction opposite from the the direction in
the step S5, the induced voltage of the phase v, which is not
conducting, is detected by the detecting circuit 13, and the
integrating circuit 20 integrates the phase-v induced voltage using
the previous integration result as the initial value.
[0058] Subsequently, in a step S8, after twice integration, the
polarity of the charge remaining in the integrating capacitor is
detected by the polarity detecting circuit 16. The detection result
v-DATA in the second data latch circuit 17b. In addition, all phase
terminals of the phase current output circuit 11 are opened, and
the charge held in the integrating capacitor in the integrating
circuit 20 is reset.
[0059] In steps S9 to S11, as in the above-mentioned steps S5 to
S7, the phase current output circuit 11 passes a pulse current from
the phase u to the phase v, the induced voltage of the phase w,
which is not conducting, is detected by the detecting circuit 13,
and is integrated by the integrating circuit 20. Subsequently, a
reverse pulse current is passed from the phase u to the phase v,
the induced voltage of the phase w, which is not conducting, is
detected by the detecting circuit 13, and the phase-w induced
voltage is integrated by the integrating circuit 20.
[0060] In the next step S12, from results of twice integration in
the integrating circuit 20, the polarity of the charge remaining in
the integrating capacitor is detected by the polarity detecting
circuit 16, and a detection result w-DATA is stored in the third
data latch circuit 17c. All phase output terminals of the phase
current output circuit 11 are opened, and the charge held in the
integrating capacitor is reset in the integrating circuit 20.
[0061] After this, in a step S13, the discriminating circuit 18
determines the position of the rotor based on detection results
u-DATA, v-DATA and w-DATA stored in the data latch circuits 17a,
17b and 17c in the steps S3, S7 and S11. More specifically, the
discriminating circuit 18 determines the rotor position according
to Table 1 from three pieces of information indicating the positive
or negative polarity stored in the data latch circuits 17a, 17b and
17c, and, from the rotor position, determines the phases at which
current conduction is started, and sends a phase selection setting
signal COMMST to the phase switching control circuit 12 to
initialize the current conduction phases.
[0062] In determining the rotor position in the step S13, it is
improbable that the polarity detection results (positive or
negative) stored in the data latch circuits 17a, 17b and 17c are
all "+" (H) or all "-" (L) and, therefore, if such a combination of
results occurs, they should be regarded as detection errors, and
the process shown in FIG. 8 returns to the step S0 to perform rotor
position detection. In a motor drive control apparatus in the
embodiment shown in FIG. 7, when the apparatus is operated in
synchronism with a clock signal CLK with a frequency of 3.5 kHz,
for example, the steps S0 to S13 can be finished in a time as short
as 2 msec. Therefore, even if the rotor position detection is
carried out over again, this has hardly any effects on the starting
time of the motor that takes several tens of msec.
[0063] FIG. 9 is a timing chart when the rotor position is detected
by supplying a pulse current to the respective phases sequentially
and detecting the induced voltages at the non-conducting phases
according to the above-mentioned procedure. In FIG. 9, u, v and w
denote the output voltages of the phases of the phase current
output circuits 11, Iu, Iv and Iw denote the currents that flow in
the field coils Lu, Lv and Lw, SNS denotes an ON/OFF control signal
for integrating actions to the integrating circuit 20, RST denotes
a reset signal to discharge the charge of the integrating
capacitor, LTA, LTB and LTC denote signals for giving latch timing
to the data latch circuits 17a, 17b and 17c, JDG denotes a signal
for giving discrimination timing to the discriminating circuit 18,
and COMMST denotes a timing signal which the discriminating circuit
18 issues to initialize the phase selection in the phase switching
control circuit 12 based on a discrimination result. Clock cycles
T0 to T13 in FIG. 9 respectively correspond to steps S0 to S13 in
the flowchart in FIG. 8.
[0064] FIG. 10 shows an example of system configuration including a
motor driver unit, which includes a motor drive control apparatus
according to another embodiment of the present invention, and which
is used in a hard disk storage device. The circuit blocks and
circuit elements located in a range enclosed by a broken line 210
in FIG. 10 are formed on one semiconductor substrate, such as a
single crystal silicon chip, but they are not to be construed as
restrictive.
[0065] In FIG. 10, the circuits designated by the same reference
numerals as in FIG. 7 are the circuits, which have or include the
same functions. Specifically, reference numeral 11 denotes a phase
current output circuit that selectively and sequentially supplies
current to the three-phase field coils Lu, Lv and Lw of a spindle
motor to rotate the disks of a hard disk device, 12 denotes a phase
switching control circuit to supply to the phase current output
circuit 11 a signal for selection of the phases through which to
pass a current (phase selection control signal), 19 denotes a
timing circuit to generate control signals to the above-mentioned
circuit blocks 11 through 18 based on a clock signal CLK.
[0066] In this embodiment, out of the circuit blocks shown in FIG.
7 (or FIG. 6), the induced voltage detecting circuit 13, connected
to the output terminals U, V and W of the phase current output
circuit 11, for detecting the induced voltages, the integrating
circuit 20 (or sample-and-hold circuits 14a and 14b, and an adder
15) for integrating induced voltages detected by the induced
voltage detecting circuit 13, the polarity detecting circuit 16 for
detecting the polarity of integration results (or addition
results), the data latch circuits 17a, 17b and 17c for storing
polarity detection results, and the discriminating circuit 18 for
discriminating the rotor position, that is, a pair of phases
through which a current is conducted in the first place from
detection results stored in the data latch circuits 17a, 17b and
17c are collectively shown as a single start current conduction
phase determining circuit 21.
[0067] In this embodiment, the start current conduction phase
determining circuit 21 is connected to external terminals P1 and P2
on the chip, and the terminals P1 and P2 are connected to an
externally-mounted discrete capacitor Ci as the integrating
capacitor of the integrating circuit. This integrating capacitor
serves to eliminate noise in detected voltages in the induced
voltage detecting circuit 13 that detects the induced voltages at
the non-conducting phases to determine start current conduction
phases with high accuracy. This embodiment is particularly
effective in a case where the phase current output circuit 11 is
formed by a bipolar transistor. This is because large noise is
contained in the induced voltages at the non-conducting phases when
the phase current output circuit 11 is a bipolar transistor type
than when it is a MOSFET type.
[0068] In FIG. 10, 23 denotes a back e.m.f. detecting circuit that
monitors the voltages at the output terminals U, V and W of the
phase current output circuit 11 when they are non-conducting,
detects zero-cross points of the back e.m.f., and gives a phase
switching timing signal to the phase switching control circuit 12,
22 denotes a PLL (phase locked loop) circuit including a
voltage-controlled oscillator (VCO) that generates an oscillating
signal required to give phase switching timing to the phase
switching control circuit 12 during constant-speed rotation based
on an output signal of the back e.m.f. detecting circuit 23, 24
denotes a brake control circuit for forcibly applying an induction
brake by shorting all field coils by turning off the power supply
switch Qsw of the phase current output circuit 11 when bringing the
motor to a stop, and 25 denotes a speed control circuit for
controlling the motor speed by detecting the current flowing in the
phase current output circuit 11, and, in response to a
speed-related command signal SPNCTL from a microcomputer,
increasing the rotation speed by increasing the current applied to
the phase current output circuit 11 or reducing the speed by
decreasing the applied current.
[0069] The PLL circuit 22 is connected to external terminals P3, P4
and P5 provided on the chip, and the external terminals P3, P4 and
P5 are connected with externally-mounted elements, such as
capacitors C0 and C1 and a resistance R1, which form a loop filter
of the PLL, and a capacitor C2 and a resistance R2, which determine
an oscillation frequency of the VCO. The parts mounted on the motor
driver IC chip 210 include a protecting circuit 26 for detecting
the temperature of the chip and bringing the operation of the
circuit to a stop, a boosting circuit 27 for boosting the gate
voltage to make it possible to sufficiently drive MOSFET's used, a
voltage regulator 28 to supply a power source voltage to the IC or
LSI provided around the motor driver IC chip 210, and a VCM drive
control circuit 30 for driving the voice coil motor to move the
magnetic heads, but they should not be construed as
restrictive.
[0070] The VCM drive control circuit 30 comprises a VCM driving
circuit 31 for outputting current to drive the driving coil L VCM
of the voice coil motor, a serial port 32 for serial transmission
and reception to and from the microcomputer, a D/A converter
circuit 33 for converting control data received from the
microcomputer into an analog signal and supplying to the VCM
driving circuit 31, a back e.m.f. detecting circuit 34 for
detecting the back e.m.f. of the coil L VCM to obtain speed
information when starting the motor, an A/D converter circuit 35
for converting a detected back e.m.f. into a digital signal, a
power supply voltage monitoring circuit 36 for monitoring the
levels of power supply voltages Vss and Vdd to detect power
cut-off, and a head retraction drive circuit 37 for controlled
driving of the coil L VCM to enable the magnetic heads to retract
to outside the disk surface when power cut-off is detected.
[0071] The above-mentioned serial port 32 sends and receives serial
data DATA based on a serial clock SCLK or a load instruction signal
LOAD from the microcomputer and generates control signals, such as
an enable signal VCMEN to the VCM driving circuit 31 based on data
received. The serial port 32 also sends to the microcomputer an A-D
converted version of a back e.m.f. induced in the coil LVCM when
the motor is started, the back e.m.f. being detected by the back
e.m.f. detecting circuit 34 for obtaining speed information from
the detected back e.m.f. Thus, the microcomputer control the motor
speed by monitoring motor speed information so that the magnetic
head is prevented from falling on the hard disk surface faster than
a specified speed.
[0072] Further, the serial port 32 has a function to generate an
enable EN signal to the timing generating circuit 19 of the spindle
motor control system based on data received from the microcomputer,
and generates control signals, such as a phase selection setting
signal COMM. Note that when the phase switching control circuit 12
starts the motor by a phase selection setting signal COMMST
supplied from the start current conduction phase determining
circuit 21 as in the above-mentioned embodiment, it becomes
unnecessary to send a phase selection setting signal COMM from the
microcomputer. However, without mounting the discriminating circuit
18 for discriminating the start current conduction phases from a
polarity detection result in the start current conduction phase
determining circuit 21 and if it is arranged that the microcomputer
receives information from the latch circuits 17a to 17c, which
store polarity data, and determines and sets a pair of phases for
start current conduction in the phase switching control circuit 12,
the above-mentioned route passing through the serial port 32 can be
used to initialize the phase switching control circuit 12.
[0073] Meanwhile, in the motor driver unit in this embodiment,
there are provided a power terminal P6 for a power source voltage
Vss of 5V for example, a power terminal P7 for a power supply
voltage Vdd of 12V or 5V, and a set of power terminals P8 for
ground potential (0V). To the power terminal P7, 12V is applied for
use in a 3.5-inch hard disk device, or 5V is applied for use in a
2.5-inch hard disk device. P11 to P14 denote the terminals
connected to the terminals of the field coils of a spindle
motor.
[0074] FIG. 11 shows a control procedure from starting of a motor
till a constant speed drive in the motor driver unit, which
includes the start current conduction phase determining
circuit.
[0075] In this motor driver unit, when a start signal is given by
the microcomputer, the start current conduction phase determining
circuit 21 detects rotor position to begin with (step S21). This
rotor position detection is performed by the steps S1 to S12 in the
flowchart in FIG. 8, which has been described. When the rotor
position has been detected, a decision is made in a step S22
whether rotor data are all "L" (low level) or all "H" (high level),
if the decision result is "Yes", which means that data are all "L"
or all "H", rotor position determination (step S21) is performed
again. It ought to be noted that the step S22 corresponds to the
S13 in FIG. 8. If the decision result is "No" in the step S22,
which means that position data are neither all "L" nor all "H", the
phases for start current conduction are set in the phase switching
control circuit 12 by a signal COMMST based on detection results
from the start current conduction phase determining circuit 21
(step S23).
[0076] Subsequently, the phase switching control circuit 12
controls the phase current output circuit 11 to change over the
coils that are excited sequentially to conduct a drive current to
the coils of the motor, to start synchronous driving (step S24).
When the rotor starts to rotate normally, back e.m.f develops in
the non-conducting phases, and a decision is made in the next step
S25 whether the back e.m.f. detecting circuit 23 detected back
e.m.f. If the back e.m.f. was not detected, a decision is made that
the motor has not started, and the process returns to the step 21
to perform rotor position detection again. On the other hand, if
back e.m.f. was detected, in a step S26, back e.m.f. driving is
performed which switches over the conducting phases according to
timing of the zero-cross points detected by the back e.m.f.
detecting circuit 23 and the rotation is accelerated by an increase
of current passed through the coils, and the motor enters
constant-speed driving (step S27).
[0077] FIG. 12 is a block diagram of an example of a hard disk
device as a system including a motor driver unit according to one
embodiment of the present invention.
[0078] In FIG. 12, reference numeral 100 denotes a recording medium
such as a magnetic disk, 110 denotes a spindle motor to drive the
magnetic disk 100, 120 denotes a magnetic head including a write
head and a read head, and 130 denotes a voice coil motor to move
the arm assembly with the magnetic heads 120. Reference numeral 210
denotes a motor driver unit that can be realized by embodying the
present invention, and the motor driver unit 210 drives both the
spindle motor 110 and the voice coil motor 130.
[0079] Reference numeral 220 denotes a read/write amplifier for
amplifying a current, produced according to magnetic changes
detected by the magnetic head 120 to transmit a readout signal to a
data channel processor 230, and for amplifying a write pulse signal
from the data channel processor 230 to supply a drive current to
the magnetic head 120. Reference numeral 240 denotes a hard disk
controller for receiving readout data RDT sent from the data
channel processor 230, performing an error correcting process
thereon and performing an error correction coding process on write
data from the host computer to supply the processed data to the
data channel processor 230. The data channel processor 230 performs
a modulation/demodulation process suitable for digital magnetic
recording and carries out a signal process, such as waveform
shaping or the like taking magnetic recording characteristics into
account.
[0080] Reference numeral 250 denotes an interface controller that
controls exchange of data between this system and external
equipment, and the hard disk controller 240 mentioned above is
connected to a host computer, such as the microcomputer of a
personal computer, through the interface controller 250. Reference
numeral 260 denotes a microcomputer that performs a comprehensive
control of the whole system and calculates a sector position from
address information supplied from the hard disk controller 240, and
270 denotes a buffer cache memory for temporarily storing read data
read at high speed from the magnetic disk. The microcomputer 260
determines the operation mode from a signal sent by the hard disk
controller 240, and controls the related parts of the system
according to the operation mode.
[0081] The motor driver unit 210, as described above, comprises a
spindle motor drive part and a voice coil motor drive part. By a
signal from the microcomputer 260, the spindle motor drive part is
servo-controlled to make the relative speed of the heads constant
and the voice coil motor drive part is servo-controlled to make the
center of the head coincident with the center of a truck.
[0082] The hard disk control system 200 is formed by the motor
driver unit 210, the read/write amplifier 220, the data channel
processor 230, the hard disk controller 240, the interface
controller 250, the microcomputer 260, and the cache memory 270.
The hard disk device is formed by the control system 200, the
magnetic disks 100, the spindle motor 110, the magnetic heads 120,
and the voice coil motor 130.
[0083] Description has been made of the embodiments made by the
inventors. However, the present invention is not limited to those
embodiments, but obviously many changes and modifications of the
present invention may be made without departing from the spirit or
scope of the invention. For example, in the above-mentioned
embodiments, description has been made using a three-phase motor as
an example, but the present invention is not limited to three-phase
motors, but may be applied to the driving circuits of two-phase
motors and four-phase or other polyphase motors. Further, in those
embodiments, the motor driver unit described has been a composite
type that includes not only the driving circuit of the spindle
motor but also the driving circuit of the voice coil motor mounted
on one semiconductor chip. However, needless to say, the present
invention may be applied to a semiconductor integrated circuit
having only the spindle motor driving circuit mounted on it.
[0084] Moreover, description has centered around the field as the
backdrop of the invention in which the invention made by the
inventors is applied to the motor driver unit of the hard disk
storage device, but the present invention is not limited to this
area and may be utilized in motor driver units for driving
brushless motors, such as a motor to drive the polygon mirror of a
laser beam printer or a motor for an axial flow fan.
[0085] According to the embodiments of the present invention, it is
possible to realize a semiconductor integrated circuit for
brushless motor drive control and a brushless motor drive control
apparatus, which are capable of preventing a reverse rotation when
starting the motor by detecting the rotor position relative to the
stator with less errors to determine field coils at which current
conduction is started.
* * * * *