Method and apparatus for driving an optical pickup of an optical information recording and reproducing apparatus

Method and apparatus for driving an optical pickup of an optical information recording and reproducing apparatus having the optical pickup movable on an information track of an optical information recording medium having information tracks formed thereon side by side, and an optical pickup drive device for intermittently moving the optical pickup, wherein a distance of movement in one intermittent movement of the optical pickup is smaller than the pitch of the information tracks.

BACKGROUND OF THE INVENTION 
The present invention relates to method apparatus for driving an optical 
pickup of an optical information recording and reproducing apparatus, and 
more particularly to a method and apparatus for driving an optical pickup 
of an optical information recording and reproducing apparatus having the 
optical pickup movable on an information track of an optical information 
recording medium having information tracks formed thereon side by side and 
optical pickup moving means for intermittently moving the optical pickup. 
A prior art optical information recording and reproducing method is first 
explained. 
FIG. 1 shows an optical information recording and reproducing apparatus. In 
FIG. 1, numeral 1 denotes an optical information recording medium which is 
reciprocated in an X direction during recording and reproducing 
operations, numeral 2 denotes information tracks which includes first to 
nth information tracks 21-2n, numeral 3 denotes an optical pickup, numeral 
7 denotes an objective lens, and .DELTA.A denotes a movable range of the 
objective lens 7 for tracking. The objective lens 7 is moved by an 
actuator (which usually comprises a coil and a magnet), not shown. Numeral 
4 denotes optical pickup moving means, numeral 5 denotes a ball screw, and 
numeral 6 denotes a stepping motor. The optical pickup 3 is movable in a Y 
direction by the optical pickup drive means. A symbol .theta. represents 
an angle between the X direction of the movement of the optical 
information recording medium 1 and the information tracks 2 due to a 
setting error (skew angle), .DELTA.T represents a distance of movement of 
the objective lens 7 from one information track to an adjacent track (for 
example, from a track 2k to a track 2k+1), and .DELTA.L represents a 
distance of movement in the Y direction of the optical pickup 3 or the 
objective lens 7 for recording or reproducing information on or from one 
information track (for example, the track 2k) when the optical information 
recording medium 1 is reciprocated in the X direction. 
When information is to be recorded or reproduced, the optical information 
recording medium 1 is normally reciprocated in the X direction and the 
information is recorded or reproduced on or from the information track 2 
by using the objective lens 7. Because of the skew angle .theta. due to 
the setting error, the objective lens 7 is moved in the Y direction while 
the medium 1 is moved in the X direction in order to record or reproduce 
one track (for example, the track 2k) of information, and if the track 
cannot be traced by the Y direction movement of the objective lens 7, the 
optical pickup 3 is intermittently moved to prevent the objective lens 7 
from being deviated from the information track 2k. 
The movable range .DELTA.A of the objective lens 7 and the distance 
.DELTA.L of movement of the objective lens 7 which is to be moved for 
recording and reproducing information due to the skew angle usually has 
the following relationship: 
EQU .DELTA.A&lt;.DELTA.L 
As a result, the optical pickup 3 must be moved in the Y direction by the 
optical pickup drive means 4. Assuming that the optical pickup 3 is moved 
by a distance .DELTA.P' in one intermittent movement, the objective lens 7 
must be moved by a distance -.DELTA.P' (the same distance as the distance 
of movement of the optical pickup 3 but in the opposite direction) in 
order to prevent the objective lens 7 from being deviated from the 
information track 2k. 
Usually, the distance of movement .DELTA.P' of the optical pickup 3 and the 
distance of movement .DELTA.T of the objective lens 7 when it is moved 
from one information track to the adjacent track are selected to meet a 
relationship 
EQU .DELTA.P'&gt;.DELTA.T 
because the larger .DELTA.P' is, the larger may be the Y direction velocity 
of the optical pickup 3. 
FIG. 2 shows a characteristic curve of the distance of movement of the 
optical pickup versus time in the optical pickup drive method for the 
prior art optical information recording and reproducing apparatus. In FIG. 
2, .DELTA.P" represents a secondary oscillation amplitude generated when 
the optical pickup 3 is moved in the Y direction by the distance 
.DELTA.P'. If .DELTA.P' is too large compared to .DELTA.T, the secondary 
oscillation amplitude .DELTA.P" is equal to .DELTA.T or 
.DELTA.P"&gt;.DELTA.T. Accordingly, the distance of movement of the objective 
lens 7 which is moved in the opposite direction to the optical pickup 3 
must be determined by taking -.DELTA.P' as well as the secondary 
oscillation amplitude .DELTA.P" of the optical pickup 3 into 
consideration. Otherwise, the objective lens 7 is moved to the adjacent 
information track and the information will not be correctly recorded or 
reproduced. When .DELTA.P" is smaller than .DELTA.T, .DELTA.P" cannot be 
neglected because the objective lens 7 may be moved beyond the current 
information track. 
Thus, the object lens 7 must be instantly moved in the opposite direction 
upon the movement of the optical pickup 3. Thus, a large current is 
usually supplied to the coil of the actuator which drives the objective 
lens 7 to increase the speed of the objective lens 7. 
However, in such a prior art method for driving the optical pickup, the 
wire diameter of the coil of the actuator is large, the mass of the 
actuator is large, a large current is required and a large magnet for the 
actuator is required. As a result, it is not suitable to the high speed 
drive of the objective lens. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide a method and apparatus 
for driving an optical pickup of an optical information recording and 
reproducing apparatus having the optical pickup movable on an information 
track of an optical information recording medium having information tracks 
formed thereon side by side and optical pickup drive means for 
intermittently moving the optical pickup. According to the present 
invention, this is achieved by means of a system in which the distance of 
movement of the optical pickup in one intermittent movement is smaller 
than the pitch of the information tracks.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The preferred embodiments of the present invention will now be described 
with reference to the drawings. 
FIG. 3 shows a characteristic curve of a distance of movement of an optical 
pickup versus time in an embodiment of a method for driving the optical 
pickup of an optical information recording and reproducing apparatus of 
the present invention. 
In FIG. 3, .DELTA.T represents a distance of movement of the objective lens 
7 when it is moved from one information track to an adjacent information 
track (for example, from a track 2k to a track 2k+-1), .DELTA.P represents 
a Y direction distance of movement of the optical pickup 3 in one 
incremental movement, and .DELTA.P"' represents a secondary oscillation 
amplitude generated when the optical pickup 3 is moved in the Y direction 
by .DELTA.P. As shown in FIG. 3, .DELTA.P is selected such that 
.DELTA.P&lt;.DELTA.T and N.multidot..DELTA.P.gtoreq..DELTA.T, where N is the 
number of times of intermittent movement of the optical pickup 3. Thus, 
the Y direction secondary oscillation amplitude .DELTA.P"' of the optical 
pickup 3 is much smaller than .DELTA.T and the recording or reproducing 
operation of information by the objective lens 7 is not affected by the 
secondary oscillation amplitude .DELTA.P"' of the optical pickup 3. 
Thus, since the secondary oscillation amplitude .DELTA.P"' of the optical 
pickup 3 need not be essentially considered for correct movement of the 
objective lens 7, a current to be supplied to the actuator may be smaller 
than that supplied to the actuator used in the prior art method for 
driving the optical pickup of the optical information recording and 
reproducing apparatus, and the magnet may also be smaller. As a result, a 
high speed drive of the optical pickup 3 is attained. Because 
.DELTA.T&gt;.DELTA.P, .DELTA.T&gt;&gt;.DELTA.P"' and a control error due to the 
movement of the optical pickup 3 is reduced and .DELTA.T can be reduced. 
Thus, a memory capacity of the optical information recording medium can be 
increased. 
In accordance with the method for driving the optical pickup of the optical 
information recording and reproducing apparatus of the present invention, 
the high speed drive of the optical pickup is attained, the high access 
speed of information is attained, the control error due to the movement of 
the optical pickup is reduced, and the memory capacity of the information 
recording medium is increased. 
An embodiment of a driver for the optical pickup 3 is now explained. 
FIG. 4 shows a functional diagram of the information recording and 
reproducing apparatus for the optical card. Numeral 106 denotes a motor 
for driving the optical information recording medium 1 in a direction of 
the narrow, numeral 107 denotes a light source such as a semiconductor 
laser, numeral 108 denotes a collimeter lens, numeral 109 denotes a beam 
splitter, numeral 7 denotes an objective lens, numeral 111 denotes a 
tracking coil, numeral 112 denotes a focusing coil, numerals 113 and 114 
denote focusing lenses, numerals 115 and 116 denote photo-electric 
conversion elements, numeral 117 denotes a tracking control circuit, 
numeral 118 denotes a focusing control circuit, numeral 119 denotes a 
system controller for controlling the optical information recording and 
reproducing apparatus and numeral 120 denotes a signal bus including a 
plurality of lines to and from the system controller 119. 
FIG. 5 shows a tracking control circuit 117 of FIG. 4. Numeral 201 denotes 
an amplifier for amplifying a signal from the photo-electric converter 
115, numeral 202 denotes a phase compensation circuit for stably and 
precisely carrying out auto-tracking (AT), numeral 203 denotes a drive 
amplifier for driving a tracking coil 111, numeral 204 denotes a low pass 
filter, numeral 205 denotes a window comparator, numeral 120a denotes a 
drive pulse generated to drive the stepping motor 6 and numeral 120b 
denotes a rotation direction signal for commanding a rotation direction of 
the stepping motor 6. 
Currents are supplied to the tracking coil 111 and the focusing coil 112 by 
commands from the control circuits 117 and 118 in accordance with the 
tracking signal and the focusing signal detected by the photoelectric 
conversion elements 115 and 116, to drive the objective lens 110 to effect 
the auto-tracking (AT) and the auto-focusing (AF). 
When the skew angle .theta. is large and the displacement of the objective 
lens 7 is large, it is necessary to rotate the stepping motor 6 to drive 
the optical pickup 3 until the distance across which the objective lens 7 
is to be moved is reduced, in the opposite direction to that of the 
movement of the objective lens 7. This is carried out in the following 
manner. 
The auto-tracking error .DELTA.l is given by 
EQU .DELTA.l=l/1+G 
where l (.mu.m) is the displacement of the objective lens 7 and G is a 
servo gain of the auto-tracking. For example, when l=100 .mu.m and 
G=1000(=60 dB), 
EQU .DELTA.l=100 .mu.m/1+1000 .perspectiveto.0.1 .mu.m 
The displacement l cannot be directly detected. Thus, if the stepping motor 
6 is rotated when the displacement of the objective lens 7 is equal to or 
larger than .+-.100 .mu.m, the auto-tracking error .DELTA.l is no less 
than .+-.0.1 .mu.m and the displacement l is no less than .+-.100 .mu.m. 
The .+-.0.1 .mu.m is set in the system as a voltage .+-.Vth at a point A 
in FIG. 6. Since the signal at the point A includes a high frequency 
component, the signal is applied to the low pass filter 204 and an output 
therefrom is applied to the window comparator 205 having a compare level 
of .+-.Vth. As a result, the drive pulse 120a for driving the stepping 
motor 6 and the rotation direction signal 120b for commanding the rotation 
direction of the stepping motor 6 are generated. Those two signals are 
supplied to the stepping motor 6 to control the stepping motor 6. Time 
variations of the voltage signals 120a and 120b at the point A arc shown 
in FIG. 6. During a period Y+, the voltage at the point A is smaller than 
-Vth, and the signal 120a is produced as the drive pulse and the signal 
120b is produced as "L". During a period Y-, the voltage at the point A is 
larger than +Vth and the signal 120a is produced as the drive pulse and 
the signal 120b is produced as "H". Thus, the stepping motor 6 is 
incremented in the opposite direction to that in the period Y+ so that the 
optical pickup 3 is incremented in the Y direction. During a period other 
than the periods Y+ and Y-, the voltage at the point A is smaller than 
.+-.Vth and the signal 120a is not produced as the drive pulse and the 
stepping motor 6 is not rotated. As the optical pickup 3 is incremented, 
the objective lens 7 is incremented in the opposite direction. 
In this manner, the objective lens 7 of FIG. 4 is always kept within the 
information track of FIG. 1.