Pick-up control circuits for disc information reproducing apparatus

Pick-up control circuits for disc information reproducing apparatus. The apparatus includes a carriage, a source of a light beam mounted in the carriage, a focus lens for placing the light beam on a disc, the focus lens being mounted on a standard position in the carriage but movable by a prescribed range from the standard position, a circuit for detecting a tracking error signal responsive to a deviation of the light beam from a center of the track, a lens actuator for driving the focus lens to deviate from the standard position, a carriage actuator for driving the carriage to move in the radial direction in respect of the disc, a power source for applying a drive voltage to the carriage actuator, a switch connected between the power source and the carriage actuator, and a circuit for controlling the switch to apply the drive voltage intermittently to the carriage actuator, so that focus lens is moved to the standard position on or before reaching an end of the movable range.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates generally to an apparatus for reproducing 
information recorded on optical record discs, such as digital audio discs 
or video discs, and more particularly, to drive control circuits for 
pick-up devices of a disc information reproducing apparatus. 
2. Description of Related Art 
There have been provided optical record discs which store optically 
recorded information data or signals such as digitized audio signals, 
video or image signals and record disc reproducing apparatus for 
reproducing the recorded information data. Such the optical record discs 
for example compact discs (CD) (a type of digital audio discs), optical 
video disc, optical discs and the like are so arranged that digital data 
intended for high density recording are recorded in the form of pit 
strings forming a spiral track or a plurality of concentric tracks on one 
side of the disc and reproduced through reading the pit strings by means 
of a transducer means such as an optical pick-up device using laser beams. 
The optical pick-up device is provided with a lens for placing the laser 
beam on the record disc and a lens actuator for controlling the laser beam 
placing lens, etc., and a carriage thereof so that the pick-up device may 
accurately follow or trace the continuous concentric tracks or the spiral 
track. The range that the beam placing lens may move in the pick-up device 
is limited to, e.g., the range corresponding to dozens of tracks or so. 
Additionally, there is further provided a pick-up actuator for moving the 
pick-up device radially with respect to the disc surface, in the disc 
information reproducing apparatus. 
Therefore, the disc information reproducing apparatus is so provided that 
the pick-up device may track the continuous concentric tracks or the 
spiral track through a cooperation of the lens actuator for controlling 
the beam placing lens and the pick-up actuator for controlling the pick-up 
device. Drive signals for the lens actuator and the pick-up actuator are 
usually obtained from a tracking error signal obtained in response to 
deviation of the laser beam from the center of the track. A lens actuator 
drive signal works for making the beam placing lens deviate from its 
standard position in the pick-up device, while a pick-up drive signal 
works for moving the pick-up device so that the deviation of the beam 
placing lens from the standard position decreases. The lens actuator may 
move the beam placing lens in response to the lens actuator drive signal 
with a relatively high sensitivity because the beam placing lens has a 
relatively light mass, while the pick-up actuator may move the beam 
placing lens in response to the lens actuator drive signal with a 
relatively low sensitivity because the pick-up device has a relatively 
heavy mass. Moreover, there are a large friction and a backlash in a 
mechanical coupling between the pick-up device and the pick-up actuator. 
Therefore, in the reproducing operation for continuously tracing the 
concentric tracks or the spiral track radially in reference to the record 
disc, the pick-up device moves intermittently after the beam placing lens 
is deviated from the standard position in each direction in respect to the 
record disc for about 200 micrometers (.mu.) corresponding to a a range of 
about 120 number of tracks. 
Further, in conventional disc information reproducing apparatus, the 
pick-up drive signal or voltage is continually applied to the pick-up 
actuator, while the pick-up device is left unmoved until the pick-up drive 
voltage has increased to a level sufficient to drive the pick-up device 
against the mass, the friction and the backlash. In other words, the 
pick-up device is moved intermittently in spite of the pick-up drive 
voltage being always applied thereto. This causes power responding to the 
pick-up drive voltage to be consumed wastefully during the period that the 
pick-up device is left unmoved. The power consumption has become a serious 
problem for battery-driven record disc repoducing apparatus type. Further, 
there has occured an undesired mechanical vibration or a noise at the 
mechanical coupling between the pick-up device and the pick-up actuator 
during the period that the pick-up device is left unmoved. 
SUMMARY OF THE INVENTION 
Accordingly, it is an object of the present invention to provide a disc 
information reproducing apparatus which may operate with a relatively low 
power consumption. 
It is another object of the present invention to provide a disc information 
reproducing apparatus which may operate with a small mechanical vibration. 
It is still another object of the present invention to provide a disc 
information reproducing apparatus which may operate with a small noise. 
These and other objects of the present invention are achieved in a disc 
information reproducing apparatus. The apparatus includes a carriage, a 
source of a light beam mounted in the carriage, a focus lens for placing 
the light beam on a disc, the focus lens being mounted on a standard 
position in the carriage but movable by a prescribed range from the 
standard position, a circuit for detecting a tracking error signal 
responsive to a deviation of the light beam from a center of the track, a 
lens actuator for driving the focus lens to deviate from the standard 
position, a carriage actuator for driving the carraige to move in the 
radial direction with respect to the disc, a power source for applying a 
drive voltage to the carriage actuator, a switch connected between the 
power source and the carriage actuator, and a circuit for controlling the 
switch to apply the drive voltage intermittently to the carriage actuator, 
so that focus lens is moved to the standard position on or before reaching 
an end of the movable range. 
Additional objects, advantages, and features of the present invention will 
further become apparent to persons skilled in the art from a study of the 
following description and of the accompanying drawings, in which:

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The present invention will now be described in detail with reference to 
FIGS. 1 to 9. Throughout the drawings, like reference numerals or letters 
are used to designate like or equivalent elements. 
Referring first to FIG. 1, description will be made to a fundamental block 
diagram of a record disc reproducing apparatus according to the present 
invention. 
In FIG. 1, an optical record disc 11 is provided to rotate about its 
center. Optical record disc 11 bears on its surface a plurality of 
concentric information recording tracks tracks or connected with each 
other in entirely a spiral track. A symbolically represented pick-up 
device 12 is movably supported on a feeder 25. Feeder 25 is driven by a 
pick-up actuator 24 so that pick-up device 12 moves radially in reference 
to the surface of disc 11. Pick-up device 12 comprises a carriage 12a, a 
source of a light beam, e.g., a laser diode 13, a collimator lens 14, a 
semi-transparent mirror 15, a device for placing laser beam LB on record 
disc 11, e.g., a focus lens 16, a split-photosensor 17, a lens actuator 21 
and a lens deviation sensor 10. Laser diode 13 radiates a laser beam LB. 
Collimator lens 14, semi-transparent mirror 15 and focus lens 16 guide 
laser beam LB to optical record disc 11 so that laser beam LB is placed on 
optical record disc 11 in a form of light spot. Pick-up device 12 then 
sequentially scans the concentric tracks or the spiral track with the 
light spot of laser beam LB, by moving radially in a direction of an arrow 
A in the drawing during a reproducing operation. Laser beam LB is 
reflected by optical record disc 11 and then applied to split-photosensor 
17 through focus lens 16 and semi-transparent mirror 15. Split-photosensor 
17 detects from the reflected laser beam LB information relating to a 
state, e.g., a strength of the reflected laser beam LB and produces an 
electrical signal responding to the information. 
Focus lens 16 is movably mounted on carriage 12a of pick-up device 12, 
while lens actuator 21 and lens deviation sensor 10 are associated with 
focus lens 16. Lens actuator 21 controls a position of focus lens 16 so 
that the light spot of laser beam LB follows a center of a prescribed 
track in, e.g., the reproducing operation. The control of focus lens 16 
may be made by a conventional tracking control system as described below. 
The tracking control system is made in a servo loop which is comprised of 
split-photosensor 17, a tracking error circuit 18, a phase compensation 
circuit 19, a lens actuator drive circuit 20 and lens actuator 21. The 
electrical signal obtained by split-photosensor 17 is applied to tracking 
error circuit 18. Tracking error circuit 18 processes the electrical 
signal so that tracking error circuit 18 produces a tracking error signal 
TE responding to a deviation of the scanning position of pick-up device 12 
from the center of the track then being scanned. Tracking error signal TE 
is applied to lens actuator drive circuit 20 through phase compensation 
circuit 19. Lens actuator drive circuit 20 produces a lens actuator drive 
signal TC responding to tracking error signal TE. Lens actuator drive 
signal TC is applied to lens actuator 21 of pick-up device 12. Lens 
actuator 21 drives focus lens 16 in response to lens actuator drive signal 
TC so as that tracking error signal TE from laser beam LB reflected from 
record disc 11 and applied through focus lens 16 and semi-transparent 
mirror 15 decreases. Therefore, focus lens 16 is driven by lens actuator 
21 so as that the light spot of laser beam LB is kept placed on the center 
of the prescribed track. 
When lens actuator 21 fails to be applied with lens actuator drive signal 
TC or lens actuator drive signal TC is negligibly small, focus lens 16 is 
kept on its standard position in pick-up device 12. However, focus lens 16 
deviates farther from the standard position as the reproducing operation 
progresses. That is, focus lens 16 is moved in the direction of arrow A by 
lens actuator 21. The deviation or the distance of focus lens 16 from the 
standard position is indicated by a graph X in FIG. 2. Deviation X of 
focus lens 16 is detected by lens deviation sensor 10. Lens deviation 
sensor 10 produces a deviation signal as indicated by a graph V10 in FIG. 
2, in response to deviation X. Deviation signal V10 is applied to a 
pick-up actuator control circuit 29 which is comprised of a set signal 
generator 30, a set-reset flip flop (S-R FF) 31 and a reset signal 
generator 32. Deviation signal V10 is applied to set signal generator 30 
and reset signal generator 32 of pick-up actuator control circit 29 in 
parallel. Both set signal generator 30 and reset signal generator 32 are, 
for example, comprised of comparator circuits. The comparator of set 
signal generator 30 is applied with a first reference signal Vr1, while 
the comparator of reset signal generator 32 is applied with a second 
reference signal Vr2 which is lower than first reference signal Vr1. When 
deviation signal V10 is the same or higher than first reference signal 
Vr1, set signal generator 30 produces a first comparison output or set 
signal S30 of a high (H) level and applies it to a set input S of S-R FF 
31. S-R FF 31 applies a control signal S31 of the H level outputted from 
its Q output to a switch 27, responding to set signal S30 of the H level 
from set signal generator 30. Switch 27 is turned ON in response to 
control signal S31 of the H level. Pick-up actuator 24 is then applied 
with a drive voltage V28 from a power supply source 28. A current flowing 
through pick-up actuator 24 therefore changes as indicated by a graph C24 
in FIG. 2. Drive voltage V28 is so set to a large value that pick-up 
actuator 24 may sufficiently actuate actuates pick-up device 12 through 
feeder 25. 
Pick-up actuator 24 transfers pick-up device 12 through feeder 25 in the 
same direction as arrow A that lens actuator 21 has moved focus lens 16 
previously. When pick-up device 12 moves in the direction of arrow A, 
focus lens 16 is so controlled that it moves in a direction of an arrow B 
opposite to arrow A. In this time, therefore, deviation signal V10 of lens 
deviation sensor 10 decreases. When deviation signal V10 has decreased 
lower than second reference signal Vr2, reset signal generator 32 produces 
a second comparison output or a reset signal S32 of the H level and 
applies it to a reset input R of S-R FF 31. S-R FF 31 is then reset so 
that control signal S31 outputted from its Q output is changed to a low 
(L) level, in response to reset signal S32 of the H level from reset 
signal generator 32. Switch 27 turns OFF in response to control signal S31 
of the L level. Pick-up actuator 24 then fails to be applied with drive 
voltage V28 from power supply source 28. 
The above-mentioned first reference signal Vr1 and second reference signal 
Vr2 for the comparators of set signal generator 30 and reset signal 
generator 32 are set as follows. A movable range of focus lens 16 in 
pick-up device 12 is limited to the range of about 200.mu. in each 
dirction of arrow A or B from the standard position. Then, first reference 
signal Vr1 is set to a voltage that lens deviation sensor 10 generates 
when focus lens 16 has deviated a prescribed distance x1 close to the end 
of the range, about 200.mu., from the standard position, while first 
reference signal Vr1 is set to a voltage of zero volts or approximately 
zero volts. Therefore, first pick-up device 12 is left unmoved but focus 
lens 16 is actuated to move in the direction of arrow A by lens actuator 
21. When focus lens 16 has moved the distance x1, deviation signal V10 of 
lens deviation sensor 10 agrees with first reference signal Vr1 so that 
S-R FF 31 of pick-up actuator control circuit 29 applies control signal 
S31 of the H level to switch 27. Switch 27 then turns ON and pick-up 
actuator 24 moves pick-up device 12 through feeder 25 in the direction of 
arrow A with drive voltage V28 which is sufficient to drive pick-up device 
12 steadily and rapidly. As a result, focus lens 16 is able to return to 
the standard position in a period p2 which is comparatively shorter than a 
period p1 of focus lens 16 having been moved previously. During period p2, 
focus lens 16 is returned to the standard position so that deviation 
signal V10 of lens deviation sensor 10 decreases. When deviation signal 
V10 of lens deviation sensor 10 agrees with second reference signal Vr2, 
S-R FF 31 is reset by reset signal S32 of H level from reset signal 
generator 32 so that control signal S31 is changed to the L level. Switch 
27 then turns OFF so that pick-up actuator 24 fails to move pick-up device 
12 through feeder 25. After pick-up device 12 has stopped, a next movement 
of focus lens 16 in the direction of arrow A for scanning following tracks 
of record disc 11 covered by the movable range of focus lens 16 is 
started. 
Referring now to FIG. 3, there is shown a second embodiment of the present 
invention. In FIG. 3, lens deviation sensor 10 is connected to the servo 
control loop for focus lens 16. That is, lens deviation sensor 10 in the 
second embodiment is indirectly associated with focus lens 16, while lens 
deviation sensor 10 of the first embodiment shown in FIG. 1 is directly 
associated with focus lens 16. Other portions of the second embodiment are 
equivalent to those of the first embodiment. Accordingly, descriptions 
will be mainly made for portions different from the first embodiment 
hereafter. 
In FIG. 3, lens deviation sensor 10 is comprised of a low pass filter (LPF) 
22 connected to the output terminal of lens actuator drive circuit 20 in 
the servo control loop for focus lens 16. LPF 22 detects a DC component of 
lens actuator drive signal TC from lens actuator drive circuit 20. An 
output V22 of LPF 22, i.e., the DC component of lens actuator drive signal 
TC responds to deviation X or the distance of focus lens 16 from the 
standard position. As a result, lens actuator drive signal TC quickly 
becomes larger for activating lens actuator 21 as the deviation X of focus 
lens 16 from the standard position progresses. Therefore, output V22 of 
LPF 22 as the DC component of lens actuator drive signal TC responds to 
deviation X of focus lens 16 from the standard position and serves for 
deviation signal V10. Deviation signal V10 is then applied to pick-up 
actuator control circuit 29 so that an operation identical to that of the 
first embodiment will be performed. 
Referring now to FIG. 4, there is shown a third embodiment of the present 
invention. In FIG. 4, switch 27, pick-up actuator 24 and a pick-up 
actuator drive circuit 23 are connected to the servo control loop for 
focus lens 16 through LPF 22 of lens deviation sensor 10. Other portions 
of the third embodiment are equivalent to those of the second embodiment. 
Accordingly, descriptions will be mainly made for portions different from 
the second embodiment hereafter. 
In FIG. 4, LPF 22 of lens deviation sensor 10 applies its output, i.e., 
output V22 of LPF 22 or deviation signal V10 to pick-up actuator drive 
circuit 23 through switch 27 as well as pick-up actuator control circuit 
29. Pick-up actuator drive circuit 23 applies to pick-up actuator 24 its 
output V23, a drive voltage responding to deviation signal V10 when switch 
27 is turned ON. As a result, pick-up actuator 24 is driven by the voltage 
based on deviation signal V10, i.e., the DC component of lens actuator 
drive signal TC or output V22 of LPF 22. However, the application of 
deviation signal V10 to pick-up actuator 24 is controlled by pick-up 
actuator control circuit 29 in a manner identical with the first or the 
second embodiment. Therefore, pick-up actuator 24 is kept deactivated 
during period p1 (see FIG. 2) in that deviation signal V10 or output V22 
of LPF 22 is lower than first referencre signal Vr1. 
The third embodiment of the present invention may be modified further as 
follows. Specifically, switch 27 and pick-up actuator 24 are able to be 
connected to the servo control loop through another low pass filter which 
is for the exclusive use of pick-up actuator 24, as opposed to LPF 22 of 
lens deviation sensor 10 which is for the exclusive use of pick-up 
actuator control circuit 29. Furthermore, pick-up actuator drive circuit 
23 may be omitted if deviation signal V10 is available for driving pick-up 
actuator 24 without any signal conversion. 
Referring now to FIG. 5, there is shown a detailed circuit diagram of an 
embodiment of pick-up actuator control circuit 29 of the first, second and 
third embodiments. In FIG. 5, an input terminal IN29 is provied for 
receiving deviation signal V10 from lens deviation sensor 10 (see FIG. 1) 
or output V22 of LPF 22 (see FIGS. 3, 4). Deviation signal V10 or V22 on 
input terminal IN29 is applied to a first and a second hysteresis circuit 
HC1 and HC2. These hysteresis circuits HC1 and HC2 respectively correspond 
to pick-up actuator control circuit 29 of the first, second and third 
embodiments. First hysteresis circuit HC1 is served for forwarding pick-up 
device 12 (see FIGS. 1, 3 and 4) in the direction of arrow A in the normal 
reproducing operation, while second hysteresis circuit HC2 is served 
rewarding reversing pick-up device 12 (see FIGS. 1, 3 and 4) in the 
direction of arrow B. Second hysteresis circuit HC2 operates when pick-up 
device 12 runs over a distance corresponding to distance x1 that focus 
lens 16 has previously moved due to an inertia of pick-up device 12 itself 
or other reasons. 
First hysteresis circuit HC1 is comprised of an operational amplifier OP1, 
a diode D1 and two resistors R1a and R1b. A non-inversed output of 
operational amplifier OP1 is connected to input terminal IN29 through 
resistor R1a, while an inversed input of operational amplifier OP1 is 
connected to a ground potential source, i.e., the ground. An output of 
operational amplifier OP1 is connected to its non-inversed input through 
resistor R1b and diode D1. Diode D1 is connected in inverse bias 
direction. Second hysteresis circuit HC2 is comprised of an operational 
amplifier OP2, a diode D2 and two resistors R2a and R2b. An inversed input 
of operational amplifier OP2 is connected to input terminal IN29, while a 
non-inversed input of operational amplifier OP2 is connected to the ground 
potential source through resistor R2a. An output of operational amplifier 
OP2 is connected to its non-inversed input through resistor R2b and diode 
D2. Diode D2 is also connected in inverse bias direction. 
The outputs of both operational amplifiers OP1 and OP2 are connected to 
base terminals of switch transistors Q1a and Q2a of NPN type respectively 
through resistors R1c and R2c. Switch transistors Q1a and Q2a respectively 
correspond to switch 27 (see FIGS. 1, 3 and 4). Switch transistor Q1a is 
connected at its collector terminal to a power input terminal PIa through 
a PNP transistor Q1b, while its emitter is connected to another power 
input terminal PIb. Switch transistor Q2a is connected at its collector 
terminal to power input terminal PIa through a PNP transistor Q2b, while 
its emitter is connected to another power input terminal PIb. Power input 
terminals PIa and PIb are provided for receiving deviation signal V10 (see 
FIG. 1) or V22 (see FIGS. 3 and 4). The base terminal of PNP transistor 
Q1b is connected to a positive input terminal of pick-up actuator 24, for 
example a motor, as well as to collector terminals of transistors Q2a and 
Q2b through a resistor R1d while the base terminal of PNP transistor Q2b 
is connected to a negative input terminal of pick-up actuator 24 as well 
as to collector terminals of transistors Q1a and Q1b through a resistor 
R2d. There is further connected a capacitor C in parallel with pick-up 
actuator 24. 
When deviation signal V10 or V22 of one polarity exceed a first prescribed 
offset voltage Vos1 given by a reverse saturation voltage Vrs of diodes, 
e.g., diode D1 and a voltage across resistor R1a, the output of 
operational amplifier OP1 changes to the H level. First prescribed offset 
voltage Vos1 corresponds to first reference signal Vr1 of the first, 
second and third embodiments. Moreover, resistor R1a is provided for 
adjusting the offset voltage. Then switch transistor Q1a turns ON so that 
NPN transistor Q2b is biased to ON while NPN transistor Q1b is left biased 
in the OFF state. Therefore, a current responding to deviation signal V10 
or V22 flows through NPN transistor Q2b, pick-up actuator 24 and switch 
transistor Q1a. As a result pick-up device 12 is driven in the direction 
of arrow B by pick-up actuator 24 through feeder 25. According to the 
movement of pick-up device 12 in the direction of arrow B, deviation 
signal V10 or V22 decreases as described previously. When deviation signal 
V10 or V22 decreases to the ground level, the output of operational 
amplifier OP1 changes to the L level. Then switch transistor Q1a turns OFF 
so that NPN transistor Q2b is biased to OFF. The ground level applied to 
operational amplifiers OP1 and OP2 corresponds to second reference signal 
Vr2 of the first, second and third embodiments. Therefore pick-up actuator 
24 is deactivated and pick-up device 12 is stopped. 
When pick-up device 12 overruns in the direction of arrow B, focus lens 16 
is deviated from the standard position in pick-up device 12 in the 
direction of arrow B. As a result, deviation signal V10 or output V22 of 
LPF 22 of another polarity is generated by lens deviation sensor 10 or LPF 
22. Deviation signal V10 or output V22 of LPF 22 of the other polarity is 
sensed at second hysteresis circuit HC2. When deviation signal V10 or 
output V22 of LPF 22 of the other polarity exceeds a second prescribed 
offset voltage Vos2 given by reverse saturation voltage Vrs of diodes and 
a voltage across resistor R2a, the output of operational amplifier OP2 
changes to the H level. Then switch transistor Q2a turns ON so that NPN 
transistor Q1b is biased to ON while NPN transistor Q2b is left biased in 
the OFF state. Therefore, a current responding to deviation signal V10 or 
output V22 of LPF 22 of the other polarity flows through NPN transistor 
Q1b, pick-up actuator 24 and switch transistor Q2a. As a result pick-up 
device 12 is driven in the direction of arrow A by pick-up actuator 24 
through feeder 25. According to the movement of pick-up device 12 in the 
direction of arrow A, deviation signal V10 or output V22 of LPF 22 of the 
other polarity decreases. When deviation signal V10 or output V22 of LPF 
22 of the other polarity decreases to the ground level, the output of 
operational amplifier OP2 changes to the L level. Then switch transistor 
Q2a turns OFF so that NPN transistor Q1b is biased to OFF. Therefore 
pick-up actuator 24 is deactivated and pick-up device 12 is stopped. 
Referring now to FIGS. 6 and 7, there are shown a fourth embodiment of the 
present invention and graphs of timing chart for explaining an operation 
of the fourth embodiment. In FIG. 6, another type of pick-up actuator 
control circuit 29a is provided but it is independent from any means for 
detecting deviation X or the position of focus lens 16. In other words, 
there is removed from FIG. 5 a deviation detecting device or apparatus 
corresponding to lens deviation sensor 10 in FIGS. 1, 3 and 4. Other 
portions of the second embodiment are equivalent to those of the first 
embodiment. Accordingly, descriptions will be mainly made for portions 
different from the first embodiment hereafter. 
In FIG. 6, pick-up actuator control circuit 29a is constituted by a timing 
signal oscillator. The timing signal oscillator is comprised of, e.g., S-R 
FF 31, a counter 33 and a clock signal oscillator 34. Counter 33 counts a 
clock signal from clock signal oscillator 34 so that it produces a set 
pulse and a reset pulse of H level with narrow pulse forms as indicated by 
graphs S33 and R33 in FIG. 7 respectively. Set pulse S33 is applied to set 
input terminal S of S-R FF 31, while reset pulse R33 is applied to reset 
input terminal of S-R FF 31. Set pulse S33 is produced with a prescribed 
period or pulse duration p3. Reset pulse R33 is also produced with the 
same period P3 but follows set pulse S33 with another prescribed period p4 
which is well shorter than period p3. The duration of period p3 may be 
determined relatively freely but within a period that focus lens 16 scans 
optical record disc 11 to the end of its movable range, while period p4 is 
determined to a period that focus lens 16 fails to overrun the standard 
position in consideration of a transfer speed of pick-up device 12. 
In reproducing operation, counter 33 applies set pulse S33 as shown in FIG. 
7 to set input terminal S of S-R FF 31 at a timing t1 that period p3 has 
lapsed from the start of the reproducing operation. S-R FF 31 then applies 
control signal S31 of the H level to switch 27 well before focus lens 16 
reaches the end of its movable range. If period p3 were considerably short 
in comparison to the period that focus lens 16 scans optical record disc 
11 to the end of its movable range, pick-up actuator 24 may steadily drive 
pick-up device 12 due to drive voltage V28 which is set to a voltage 
sufficient for activating pick-up actuator 24. Therefore, pick-up device 
12 is driven by pick-up actuator 24 in the same manner as described for 
the first embodiment shown in FIG. 1. Next, counter 33 applies reset pulse 
R33 as shown in FIG. 7 to reset input terminal R of S-R FF 31 at a timing 
t2 that period p4 has lapsed after timing t1. S-R FF 31 is then reset or 
fails to apply control signal S31 of the H level to switch 27, just before 
focus lens 16 reaches the standard position in pick-up device 12. 
Therefore, the movement of pick-up device 12 is stopped in the same manner 
as described for the first embodiment. 
Referring now to FIGS. 8 and 9, there are shown a fifth embodiment of the 
present invention and graphs of timing chart for explaining an operation 
of the fifrth embodiment. In FIG. 8, switch 27, pick-up actuator 24 and 
pick-up actuator drive circuit 23 are connected to the servo control loop 
for focus lens 16 through a LPF 22a. Other portions of the fifth 
embodiment are equivalent to those of the fourth embodiment as shown in 
FIG. 6. Accordingly, descriptions will be mainly made for portions 
different from the fourth embodiment hereafter. 
In FIG. 8, LPF 22a detects a DC component of lens actuator drive signal TC. 
The DC component of lens actuator drive signal TC, i.e., an output V22a of 
LPF 22a is applied to pick-up actuator 24 through swtich 27 and pick-up 
actuator drive circuit 23 as the drive voltage for pick-up actuator 24. 
Pick-up actuator drive circuit 23 applies to pick-up actuator 24 its 
output V23, a drive voltage responding to output V22a of LPF 22a when 
switch 27 is turned ON. As a result, pick-up actuator 24 is driven by the 
voltage based on the DC component of lens actuator drive signal TC. 
However, the application of the drive voltage to pick-up actuator 24 is 
controlled by pick-up actuator control circuit 29 in a manner identical 
with the fourth embodiment. The small ripples appearing on the waveform of 
output V22a of LPF 22a (see FIG. 9) are caused by an eccentricity of 
tracks with respect to the center of record disc 11. 
In the reproducing operation, counter 33 applies a first pulse of set pulse 
S33 as shown in FIG. 9 to set input terminal S of S-R FF 31 at a timing t1 
(see FIG. 9) that period p3 has lapsed from the start of the reproducing 
operation. Period p3 may be determined relatively freely but within a 
period that focus lens 16 scans optical record disc 11 to the end of its 
movable range in the fifth embodiment. For example, period p3 is set to a 
relatively short period close to a half of the period that focus lens 16 
scans optical record disc 11 to the end of its movable range. S-R FF 31 
then applies control signal S31 of the H level to switch 27 at timing T1, 
but output V22a of LPF 22a fails to activate pick-up actuator 24 for 
driving pick-up device 12 because output V22a of LPF 22a is lower than a 
voltage Vs3 as indicated in FIG. 9 that may activate pick-up actuator 24. 
Therefore, pick-up device 12 is kept unmoved and focus lens 16 continues 
to move in the direction of arrow A by being driven by lens actuator 21. 
Output V22a of LPF 22a then continues to increase. Counter 33 applies a 
second pulse of set pulse S33 to set input terminal S of S-R FF 31 at a 
timing t3 (see FIG. 9) that period p3 has lapsed from timimg t1, next to 
an application of a first pulse of reset pulse R33 to reset input terminal 
R of S-R FF 31 at a timing t2 (see FIG. 9) that period p4 has lapsed from 
timing t1. S-R FF 31 then applies control signal S31 of the H level to 
switch 27. Then output V22a of LPF 22a from LPF 22a is applied to pick-up 
actuator 24 through switch 27 in the ON state. At timing t3, output V22a 
of LPF 22a has increased to a sufficient voltage that may activate pick-up 
actuator 24 to drive pick-up device 12. As a result, pick-up device 12 is 
driven by pick-up actuator 24 in the same manner as described for the 
third embodiment shown in FIG. 4. 
Next, counter 33 applies a second pulse of reset pulse R33 as shown in FIG. 
9 to reset input terminal R of S-R FF 31 at a timing t4 (see FIG. 9) that 
period p4 has lapsed after timing t3. S-R FF 31 is then reset or fails to 
apply control signal S31 of the H level to switch 27, just before focus 
lens 16 reaches the standard position in pick-up device 12. Therefore, the 
movement of pick-up device 12 is stopped its movement its movement in the 
same manner as described for the third embodiment. After pick-up device 12 
has stopped, a next movement of focus lens 16 in the direction of arrow A 
for continuing the reproducing operation is started. 
The fifth embodiment may be modified further as follows. That is, pick-up 
actuator drive circuit 23 may be omitted if output V22a of LPF 22a is 
available for driving pick-up actuator 24 without any signal conversion.