Pickup-drive stabilizing apparatus for an optical disc player

A pickup driving apparatus, and particularly, a pickup-drive stabilizing apparatus for an optical disc player includes: a detector for detecting an inertia of a pickup relative to a movement speed of the pickup, when an instruction occurs to stop driving a sled motor that transversely shifts the pickup at a high speed for high-speed access; and a comparator that determines whether an inertia speed of the pickup has decelerated to within a range stable for tracking control by comparing the output signal of the detector with a preset reference signal and generates an output signal for starting the tracking control. Therefore, the pickup-drive stabilizing apparatus can stabilize the pickup of the optical disc player after performing high-speed information access on an optical disc.

BACKGROUND OF THE INVENTION 
The present invention relates to a pickup driving apparatus in an optical 
disc player, and particularly to a pickup-drive stabilizing apparatus for 
stabilizing the tracking of an optical disc player, after carrying out 
high-speed information access. 
An apparatus that records and reproduces information using an optical disc 
is known as an optical disc player. The term "tracking" applies to an 
object lens moving along a track of the optical disc having certain 
information thereon, and the term "high-speed access" refers to the pickup 
of an optical disc player traversing from one track to another track far 
removed from the first. The optical disc player shifts the pickup by 
driving a sled motor to perform the high-speed information access on the 
optical disc. 
In the conventional high-speed information access method, a sled servo 
driving signal is applied from a microcomputer to control the sled motor. 
Then, a tracking servo driving signal is applied to control a tracking 
servo. However, the tracking is very unstable after performing the 
high-speed access due to the inertia of the pickup. Due to this inertia, 
the pickup continues to move for a period even after the tracking servo 
driving signal is applied to control the tracking servo. Therefore, 
high-speed tracking is performed as soon as the microcomputer supplies the 
sled servo control signal. A problem thus occurs in that the pickup moves 
for a period because of the pickup's inertia due to the high-speed access, 
making the tracking very unstable. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide a pickup-drive 
stabilizing apparatus which can stabilize tracking after performing 
high-speed information access on an optical disc. 
To achieve the above and other objects, an optical disc player can perform 
high-speed access while transversely transferring a pickup across the 
track of an optical disc, using a pickup drive stabilizing apparatus which 
includes: 
detecting means for detecting the inertia movement speed of the pickup, 
after a drive-stop instruction of a sled motor that transversely shifts 
the pickup means at a high speed for the high-speed access; and 
a determining means that determines whether or not the inertia speed of the 
pickup has decelerated to within a range stable enough for tracking 
control by comparing the output signal of the detecting means with a 
preset reference signal, and generates an output signal for starting the 
tracking control.

DETAILED DESCRIPTION OF THE INVENTION 
Referring to FIG. 1, the tracking error signal is input to a tracking servo 
portion 30 and a pickup movement speed detector 20. Outputs of a 
controller, e.g., microcomputer 10 are connected to the tracking servo 
portion 30, a sled servo portion 40, and pickup movement speed detector 
20. The output of the tracking servo portion 30 is connected to both a 
tracking actuator 35 and sled servo portion 40 whose output is connected 
to a sled motor 45. Pickup movement speed detector 20 supplies input to 
the microcomputer 10, and further breaks down into a track zero-crossing 
portion 22 and a sled speed detector 21. The tracking error signal feeds 
track zero crossing portion 22 which is connected to the sled speed 
detector 21 whose output is the supplied input to the microcomputer 10. 
FIG. 2 is a detailed block diagram of the sled speed detector 21 shown in 
FIG. 1. 
Referring to FIG. 2, a switch SW1 controlled by an enable signal from the 
microcomputer 10 is connected between the output of the track 
zero-crossing portion 22 and a detecting means 100. A determining means 
200 is connected to an output of the detecting means 100 which includes a 
first rising edge detector 21a, a delay circuit 21b, a counter 21c, and a 
first latch 21d. The input of the first rising edge detector 21a is 
connected to the output of the switch SW1. The output of the first rising 
edge detector 21a is connected to both the input of delay circuit 21b and 
the clock terminal of first latch 21d. The output of delay circuit 21b is 
connected to the reset terminals of counter 21c and first latch 21d. The 
output of counter 21c is connected to an input of the first latch 21d. The 
determining means 200 includes a comparator 21e, a second latch 21f, and a 
reset signal generator which is second rising edge detector 21g for 
detecting the rising edge of the enable signal from microcomputer 10. The 
output of first latch 21d is connected to the input of comparator 21e 
whose output is connected to the input of second latch 21f. Second rising 
edge detector 21g also receives the enable signal, while its output is 
connected to the reset terminal of second latch 21f whose clock terminal 
is connected to the output of delay circuit 21b. The output of second 
latch 21f is connected microcomputer 10. 
FIGS. 3A to 3E show input/output waveforms of the pickup-drive stabilizing 
apparatus illustrated in FIG. 1. Here, FIG. 3A shows an output waveform of 
sled servo portion 40; FIG. 3B shows the output of track zero crossing 
portion 22; FIG. 3C shows the output of tracking servo portion 30; FIG. 3D 
shows the enable signal of microcomputer 10 that controls the sled speed 
detector 21; and FIG. 3E shows the output of sled speed detector 21. 
FIG. 4 shows input/output waveforms of the sled speed detector shown in 
FIG. 2. Here, FIG. 4A shows the inable signal input to first rising edge 
detector 21a; 4B shows the output waveform of first rising edge detector 
21a; 4C shows the output waveform of delay circuit 21b; 4D shows the 
counted value in counter 21c; and 4E shows the output waveform of second 
latch 21f. 
The operation of the present invention will now be described with reference 
to FIGS. 1 through 4. 
First, when the information on the optical disc is reproduced in the normal 
state, the microcomputer 10 supplies a normal mode control signal to 
tracking servo portion 30 and sled servo portion 40, thereby controlling 
the tracking actuator 35 and the sled motor 45. The tracking servo portion 
30 receives a tracking error signal that indicates the position of an 
object lens on the track of the optical disc, then controls tracking 
actuator 35. The sled servo portion 40 receives the output of tracking 
servo portion 30 to control the sled motor 45, thereby moving the object 
lens of the pickup. That is, during normal reproducing, the position of 
the object lens is adjusted by the tracking servo portion 30 and the 
object lens of the pickup is moved by the sled servo portion 40. 
On the other hand, when the optical disc player performs high-speed 
information access on the optical disc, microcomputer 10 outputs a control 
signal to sled servo portion 40 to make the sled servo portion 40 drive 
the sled motor, which moves the object lens. The pickup movement speed 
detector 20 calculates the movement speed of the pickup upon receiving the 
tracking error signal, then applies a tracking starting signal to the 
microcomputer 10 when the movement speed of the pickup becomes suitable 
for tracking. 
The pickup movement speed detector 20 is described with reference to FIGS. 
3A through 3E. FIG. 3A shows high-speed access operation, where sections 
a1, a2 and a3 designate the intervals where microcomputer 10 outputs 
control signal to the sled servo portion 40 to drive the sled motor 45, 
the microcomputer 10 does not output the control signal, and where 
microcomputer 10 outputs the control signal to the tracking servo 30 and 
sled servo portion 40 for driving the tracking actuator 35 and sled motor 
45, respectively. When the output of the sled servo portion 40 goes high 
as in section a1 of FIG. 3A, the output signal of the track zero crossing 
portion 22 is as illustrated in FIG. 3B. While the sled motor drives the 
pickup across the tracks, the track zero crossing portion 22 outputs a 
track zero-crossing signal from the space between tracks according to the 
reflectivity difference. The track zero-crossing signal is a logic high 
when the track is present, and is low when the track is not. Here, the 
sled speed detector 21 receives and counts the output of the track zero 
crossing portion 22, and then outputs the tracking starting signal to the 
microcomputer 10 when the speed becomes suitable for tracking. Therefore, 
the microcomputer 10 outputs the tracking control signal to the tracking 
servo portion 30 and sled servo portion 40, which in turn drives the 
tracking actuator 35 and sled motor 45. As a result, the tracking is 
stabilized. In other words, it is important to drive sled motor 45 and 
tracking actuator 35 during section a3 and after section a2, which perform 
tracking after sufficiently eliminating the object lens' inertia of 
section a2. 
Sled speed detector 21 outputs the tracking starting signal to the 
microcomputer 10 for stabilizing the tracking. To perform high-speed 
access, the microcomputer 10 supplies a control signal to the sled servo 
portion 40, and an enable signal to the sled speed detector 21. By the 
enable signal of the microcomputer 10, the switch SW1 is turned on. The 
second rising edge detector 21g detects the rising edge of the enable 
signal, and outputs the detected signal as a reset signal to the second 
latch 21f. Accordingly, the output of the track zero crossing portion 22 
is input to the first rising edge detector 21a. The first rising edge 
detector 21a detects and outputs the rising edge of the track 
zero-crossing signal to the delay circuit 21b. Delay circuit 21b outputs a 
delayed rising edge signal. The waveforms output from the first rising 
edge detector 21a and the delay circuit 21b are shown in FIGS. 4B and 4C, 
respectively. FIG. 4A illustrates the input waveform of the first rising 
edge detector 21a. Thus, the counter 21c receives the waveform shown in 
FIG. 4C at its reset terminal, and the external clock to the clock 
terminal. The counter 21c outputs the value counted as illustrated in FIG. 
4D by detecting the movement speed of the pickup with the clock signal. 
The first latch 21d receives and latches the counted value illustrated in 
FIG. 4D. The counted value that is latched to the first latch 21d is 
output to the comparator 21e using the signal output from the first rising 
edge detector 21a as a clock which is input to the clock terminal of the 
first latch 21d. The comparator 21e outputs a compared signal to the 
second latch by comparing with the reference value of the comparator 21e. 
If it is assumed that the counted value to the period of the track 
zero-crossing signal period corresponding to the movement speed of the 
pickup is "N" shown in FIG. 4D, the counter 21c continues to count until 
the period of the track zero-crossing signal exceeds the value "N". 
Therefore, when the period of the track zero-crossing signal is more than 
N, the output of second latch 21f becomes a high logic level at the 
counting point of the next period. The compared signal input to the second 
latch 21f is output to the microcomputer 10 as a tracking starting signal 
in accordance with the output signal of the delay circuit 21b which is 
provided as the clock. The Q output of second latch 21f is supplied to the 
microcomputer 10, then tracking begins. The output of the sled speed 
detector 21 is shown in FIG. 4E, and the microcomputer 10 shifts back to 
the normal mode. 
As described above, the present invention is advantageous in that the 
pickup driving of the optical disc player can be stabilized even after 
performing high-speed information access on an optical disc.