Dynamic information storage or retrieval – With servo positioning of transducer assembly over track... – Optical servo system
Reexamination Certificate
1998-02-26
2001-06-19
Edun, Mahammad (Department: 2651)
Dynamic information storage or retrieval
With servo positioning of transducer assembly over track...
Optical servo system
C369S047360
Reexamination Certificate
active
06249495
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a method for controlling stepping motors and a disk apparatus that uses a stepping motor.
In recent years, high speed accessing performance is required for disk apparatuses to feed the pick-up to a target position on the disk quickly. A disk apparatus that uses a stepping motor as a traverse motor for feeding the pick-up is already commercialized. Since the stepping motor is rotated in units of a constant basic step angle in response to the driving pulses, it is easy to open-control a strokes for feeding the pick-up and it needs no position detecting means. When using such a stepping motor for a disk apparatus, therefore, the pick-up feeding mechanism can be simplified.
However, disk apparatuses that use such a conventional stepping motor respectively have been confronted with various problems as described below. An object of the present invention is to solve such problems and provide a method for controlling stepping motors at high speeds and very accurately in an open-control that uses no detector such as a position sensor, as well as to provide a disk apparatus that uses the above-mentioned method for controlling stepping motors.
Next, various problems that will arise in disk apparatuses that use a conventional stepping motor respectively will be described in detail.
[Problems at Driving Operation of the Conventional Stepping Motors]
Hereunder, a conventional disk apparatus and a conventional method for controlling stepping motors will be explained with reference to the attached drawings.
FIG. 54
is a schematic illustration for a configuration of the conventional disk apparatus. In
FIG. 54
, a lens
107
b
is held by springs
107
c
and
107
d
above a pick-up
107
a.
The rotational movement of a stepping motor
107
f
is transmitted to the pick-up
107
a
via a feed screw
107
e.
The pick-up
107
a
makes a linear motion in the radial direction of a disk
107
j.
The disk
107
j
stores information on its helically-formed tracks and the rotation speed of the disk
107
j
is controlled by a spindle motor
1071
. Error signals from the pick-up
107
a
are transmitted to a servo means
107
g.
And, the servo means
107
g
outputs a signal for controlling the springs
107
c
and
107
d
to the pick-up
107
a
so that each error signal is cleared to 0. A system controller
107
i,
which is connected to the servo means
107
g,
an interface means
107
k,
and the spindle motor
1071
, transmits a driving command signal for feeding the pick-up
107
a
to the stepping motor controlling means
107
h
as needed. By receiving the driving command signal, the stepping motor controlling means
107
h
controls the stepping motor
107
f.
When in recording or playing back information in or from the conventional disk apparatus, the lens
107
b
keeps following up the helically-formed tracks on the disk
107
j
and the lens
107
b
changes its position gradually in the radial direction of the disk
107
j.
The servo means
107
g
detects each of such displacement values of the lens
107
b.
When the system controller
107
i
detects that the lens
107
b
has exceeded a specified displacement value, the system controller
107
i
transmits a driving command signal to the stepping motor controlling means
107
h.
By receiving the driving command signal, the stepping motor controlling means
107
h
rotates the stepping motor
107
f
step by step at fine pitches. The stepping motor controlling means
107
h
moves the pick-up
107
a
by a fine distance in the radial direction of the disk
107
j
to limit the displacement of the lens
107
b
within a low value. Then, the stepping motor
107
f
is kept at rest until the lens
107
b
exceeds the specified displacement value again.
As a means of moving the pick-up by rotating the stepping motor step by step at fine pitches, a controlling method referred to as micro-step driving operation is well known. The conventional micro-step driving method divides the basic step angle of the stepping motor into n angles (n: an integer of 2 or over) like an optical disk apparatus disclosed, for example, in Unexamined Published Japanese Patent Application Publication No. 7-272291 and changing the driving current step by step.
Next, the conventional stepping motor controlling method will be explained.
FIG. 55
is a schematic inner configuration of a general stepping motor. In
FIG. 55
, a numeral
106
a
indicates a current flowing in an A-phase coil and
106
b
indicates a current flowing in a B-phase coil. A rotator
106
c
has some pairs of N and S magnetic poles. The number of magnetic pole pairs differ among types of stepping motors. A point P on the rotator begins rotating when the current
106
a
flowing in the A-phase coil and the current
106
b
flowing in the B-phase coil are changed together. The point P stops when the balance between the magnetic force generated from those coils and the frictional load of rotation is stabilized. Positions
106
X and
106
Z indicate two points of some mechanical stability points existing on the rotator. Those two points are adjacent with each other. The rotation angle from the position
106
X to the position
106
Z is defined as the basic step angle of the stepping motor. The position
106
Y indicates one of mechanical instability points existing between the positions
106
X and
106
Z. To rotate the stepping motor by a micro-step, the rotator
106
c
must be rested at a mechanical instability position in the range of the basic step angle, as shown with the position
106
Y.
Next, the current flowing in each of the A-phase and B-phase coils of the stepping motor will be explained.
FIG. 56
is a wave form chart indicating the driving current of the conventional stepping motor. The wave form chart shown in
FIG. 56
indicates a wave form of the current in the controlling method referred to as a 1-2-phase exciting system that divides the basic step angle of the stepping motor into two angles and rotating the stepping motor in units of a 1/2 step angle. There is also another well-known controlling method, in which the basic step angle of the stepping motor is furthermore divided into n angles (n: an integer of 2 or over) and the stepping motor is rotated in units of a 1
step angle. To make it easier to understand the explanation here, a method for controlling stepping motors with a driving current as shown in
FIG. 56
will be picked up. The method divides the basic step angle into two angles, which is the least division number in the controlling methods, each of which divides the basic step angle of the stepping motor into n angles.
In
FIG. 56
, the wave form
105
a
is a driving current wave form representing the flow rate and direction of the current flowing in the A-phase coil of the stepping motor on the time axis. The wave form
105
b
is a driving current wave form representing the flow rate and direction of the current flowing in the B-phase coil of the stepping motor on the time axis. In the driving current wave forms
105
a
and
105
b,
the current flowing forward is represented by a positive value and the current flowing reversely is represented by a negative value. The current wave form, when the stepping motor is rotated forward, is changed from left to right in FIG.
56
. The current wave form, when the stepping motor is rotated reversely, is changed from right to left in FIG.
56
. If the current state is changed from
105
X to
105
Z in
FIG. 56
, it means that the state
105
Y exists between those states. In the state
105
Y, only the A-phase coil shown in
FIG. 55
is excited and the B-phase coil is not excited. Thus, the stepping motor can stop at the position
106
Y between the positions
106
X and
106
Z in FIG.
55
. This means that the motor can stop at 1/2 of the basic step angle of the stepping motor. Since the basic step angle of the stepping motor is divided into n angles such way, the stepping motor can be rotated step by step at fine pitches. And, when using such a stepping motor for feeding the pick-up of a disk app
Akagi Noritaka
Harui Masanori
Imura Masaharu
Kai Tsutomu
Kouno Kazuhiko
Akin Gump Strauss Hauer & Feld L.L.P.
Edun Mahammad
Matsushita Electric - Industrial Co., Ltd.
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