Electricity: motive power systems – Positional servo systems – With particular motor control system responsive to the...
Reexamination Certificate
2002-05-23
2003-04-01
Leykin, Rita (Department: 2837)
Electricity: motive power systems
Positional servo systems
With particular motor control system responsive to the...
C318S561000, C360S073010, C360S075000, C360S069000
Reexamination Certificate
active
06541935
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a method for controlling a stepping motor, and more particularly, to a method for controlling a tracking servo of a stepping motor used in a disc reproduction apparatus.
A digital audio compact disc (CD) may be used as a read-only memory (CD-ROM) for various types of computer-readable digital data. A disc reproduction apparatus that reproduces such a CD has a servo mechanism to control the relative position between the disc and a pickup so that the pickup can correctly trace a spiral recording track on the disc.
FIG. 1
is a schematic block diagram of a disc reproduction apparatus
100
. A spiral recording track is formed on at least one side of the disc
1
. Digital data, which complies with a predetermined format, is recorded along the recording track. For example, in a CD, pits having a predetermined length are formed on the recording track in accordance with an EFM signal, which is obtained by performing eight to fourteen modulation (EFM) on digital data. The spindle motor
2
rotates the disc
1
at a predetermined speed in accordance with a drive signal SD, which is provided from a servo control circuit
7
.
A pickup
3
, which is mounted on a sled
4
, includes a laser beam source and a sensor. In a state in which the sled
4
is attached to a drive device (not shown) and the pickup
3
is opposed to the recording track surface of the disc
1
, the pickup
3
is moved in the radial direction of the disc
1
. An actuator
5
moves the sled
4
in the radial direction of the disc
1
in accordance with a drive signal TD provided from a servo control circuit
7
.
A signal processing circuit
6
receives an output signal read from the disc
1
by the pickup
3
and performs operations such as waveform shaping and binary coding to generate the EFM signal. The EFM signal is shifted between two levels in accordance with the pits and lands formed on the recording track of the disc
1
. Based on the output signal of the pickup
3
, the signal processing circuit
6
generates a tracking error signal TE and an off track signal OT. More specifically, the pickup
3
includes a main beam source, which reads the data recorded on the disc
1
, and an auxiliary beam source, which reads the position of the main beam source relative to the recording track of the disc
1
. The signal processing circuit
6
generates the EFM signal from the read output signal of the main beam source and generates the tracking error signal TE from the read output signal of the auxiliary beam source. The tracking error signal TE is normally maintained at “0” level when the reading position of the pickup
3
relative to the disc
1
is correct. When the pickup
3
moves toward the inner side or the outer side of the disc and away from the proper position, the error signal TE shifts to a negative or positive polarity level. The signal processing circuit
6
generates the off track signal OT from a low frequency component of the EFM signal. The off track signal OT is maintained at a low level when the EFM signal is output properly (i.e., when the pickup
3
correctly reads data from the recording track of the disc
1
). When the pickup
3
moves away from the proper position and the EFM signal is thus not properly output, the EFM signal goes high.
The servo control circuit
7
receives the EFM signal, the tracking error signal TE, and the off track signal OT from the signal processing circuit
6
and generates a spindle motor drive signal SD and an actuator drive signal TD. The spindle motor drive signal SD is generated to keep the cycle of the EFM signal constant when, for example, performing constant linear velocity (CLV) control to drive the disc
1
at a constant linear velocity. Further, the spindle motor drive signal SD is generated in accordance with a reference clock signal having a constant frequency when performing constant angular velocity (CAV) control to drive the disc
1
at a constant angular velocity. The servo control circuit
7
generates the actuator drive signal TD based on the tracking error signal TE and the off track signal OT. For example, to read data from the disc
1
, the actuator drive signal TD is generated so that the tracking error signal TE becomes close to the “0” level. Such servo control rotates the disc
1
at a predetermined velocity (constant linear velocity or constant angular velocity) while the pickup
3
traces the recording track on the disc
1
to appropriately read the data recorded on the disc
1
.
The actuator
5
causes the pickup
3
and the sled
4
to take a short jump or a long jump. A short jump moves the pickup
3
within a movable range on the sled
4
. A long jump moves the sled
4
with the position of the pickup
3
in a fixed state.
In a short jump, only the pickup
3
is moved with the sled
4
in a fixed state. When the pickup
3
approaches the limit of the movable range on the sled
4
, the sled
4
is moved slightly so that the pickup
3
may further be moved on the sled
4
. The short jump is taken when reading data as the pickup
3
follows the recording track of the disc
1
.
In a long jump, the moving distance of the pickup
3
relative to the disc
1
(normally, longer than the movable range of the pickup
3
) is set, and the sled
4
moves in accordance with the set moving distance. In this state, the pickup
3
, which is substantially fixed on the sled
4
, reads signals from the disc
1
as the pickup
3
traverses the recording track on the disc
1
. The reading operation of the pickup
3
is performed to count the number of recording tracks the pickup
3
skips and not to read the data recorded on the disc
1
.
The polarity of the tracking error signal TE is inverted whenever the pickup
3
traverses the single recording track. Thus, the generated tracking error signal TE has a sine waveform when the pickup
3
consecutively traverses the recording track a number of times. Further, the generated EFM signal has a predetermined amplitude when the pickup
3
is above the recording track, and the generated EFM signal has a fixed value when the pickup
3
moves away from the recording track. Thus, the off track signal OT, which is generated from the low frequency component of the EFM signal alternately goes high and low as the pickup
3
traverses the recording track. The off track signal OT has the same cycle as the tracking error signal TE and has a phase that is either advanced or delayed by n/2 from the tracking error signal TE with respect to the moving direction of the pickup
3
(sled
4
). The number of recording tracks the pickup
3
skips is detected by counting the tracking error signal TE or the off track signal OT. The movement of the sled
4
is stopped when the pickup skips the number of recording tracks that correspond to a target distance.
When moving the sled
4
by a target distance in the radial direction of the disc
1
, the drive signal TD is generated so that the sled
4
is accelerated when the movement starts and the sled
4
is decelerated just before the position where the sled
4
is to stop. For example, referring to
FIG. 2
, from time t
0
, when the movement of the sled
4
starts, to time t
1
, when the sled
4
reaches a predetermined speed, the sled
4
is moved at a constant acceleration rate. Then, from time t
1
to time t
2
, the sled
4
is moved at a constant velocity. After time t
2
, the sled
4
is moved at a negative acceleration rate so that the sled
4
stops at time t
3
. Time t
2
is determined from the moving distance of the sled
4
and the acceleration rate during deceleration. When the moving distance of the sled
4
is relatively short or when the absolute value of the acceleration rate during deceleration is relatively small, time t
2
is set so that it is earlier than time t
1
. In this case, constant velocity movement is not performed, and acceleration is switched to deceleration at time t
2
.
When moving the sled
4
with the drive signal TD, servo control is performed while confirming the moved distance of the sled
4
on the b
Fish & Richardson P.C.
Leykin Rita
Sanyo Electric Co,. Ltd.
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