Rotation control apparatus for constant linear velocity system information recording disc

A rotation control apparatus for a CLV system disc sets an initial value based on an address signal reproduced from the CLV system disc and carries out a rotation control by use of the initial value, so that it is possible to carry out the rotation control even with respect to a CLV system disc on which an information signal is only recorded up to an intermediate position within a program region of the disc. An information signal is newly recordable in conformance with the CLV system from a position in a vicinity of the intermediate position where the previous recording had been discontinued.

BACKGROUND OF THE INVENTION 
The present invention generally relates to rotation control apparatuses for 
constant linear velocity system information recording discs, and more 
particularly to a rotation control apparatus which controls a rotation 
frequency of a constant linear velocity system information recording disc 
so that a relative linear velocity between a pickup device and the 
information recording disc is always maintained constant. 
When recording and reproducing an information signal on and from a constant 
linear velocity system information recording disc (hereinafter simply 
referred to as a CLV system disc), a rotation control is carried out so 
that a relative linear velocity between a pickup device and the disc is 
always constant. At the time of a reproduction, the relative linear 
velocity can always be maintained constant by carrying out the rotation 
control so that a value obtained by reproducing a signal which is 
pre-recorded on the disc and has a constant frequency becomes a regular 
value. For example, in the case where the information signal pre-recorded 
on the disc is a video signal, a horizontal synchronizing signal within 
the video signal is used as the signal having the constant frequency, and 
bit clock pulses are used as the signal having the constant frequency in 
the case where the information signal pre-recorded on the disc is a 
digital audio signal. 
On the other hand, at the time of a recording, the signal having the 
constant frequency is not yet recorded on the disc and it is hence 
impossible to use such a signal for the rotation control. But the relative 
linear velocity is determined by a product of the length (circumference) 
of each track turn on the disc and the rotation frequency. Hence, it is 
possible to maintain the relative linear velocity constant by controlling 
the rotation frequency of the disc inversely proportional to a radius at a 
position on the disc. Conventionally, when recording the information 
signal from the inner periphery to the outer periphery of the disc, the 
relative linear velocity is maintained constant by presetting the rotation 
frequency at an innermost peripheral position where the recording is 
started and by gradually decreasing the rotation frequency with a 
predetermined rate proportionally to the radius at each position on the 
disc. 
However, the conventional method of controlling the rotation of the disc at 
the time of the recording is only effective when continuously recording 
the information signal throughout the entire recording region on the disc 
from a recording start position to a recording end position, such as the 
case where the recording is carried out by a cutting apparatus. In the 
case where the disc is removed from the recording apparatus by 
discontinuing the recording of the information signal in the recording 
region and the recording is resumed after a predetermined time has elapsed 
by once again loading the disc on the recording apparatus so as to newly 
record an information signal from a position on the disc where the 
previous recording had been discontinued, it is impossible to control the 
relative linear speed according to the conventional method. 
SUMMARY OF THE INVENTION 
Accordingly, it is a general object of the present invention to provide a 
novel and useful rotation control apparatus for CLV system disc, in which 
the problems described heretofore are eliminated. 
Another and more specific object of the present invention is to provide a 
rotation control apparatus for CLV system disc, in which an initial value 
is set based on an address signal reproduced from the CLV system disc and 
a rotation control is carried out by use of the initial value. According 
to the rotation control apparatus of the present invention, it is possible 
to carry out the rotation control even with respect to a CLV system disc 
on which an information signal is only recorded up to an intermediate 
position within a program region of the disc, so that an information 
signal can be newly recorded in conformance with the CLV system from a 
position in a vicinity of the intermediate position where the previous 
recording had been discontinued. 
Other objects and further features of the present invention will be 
apparent from the following detailed description when read in conjunction 
with the accompanying drawings.

DETAILED DESCRIPTION 
FIG. 1 shows an embodiment of the rotation control apparatus for CLV system 
disc according to the present invention. As shown in FIG. 2, a CLV system 
disc 11 comprises a program region 30 in which an information signal is to 
be recorded and reproduced, and one ring-shaped track 31 which is 
pre-recorded with a rotation control signal having a constant period. The 
track 31 is formed on the inner peripheral side of the program region 30. 
A lead-in region 32 is provided between the track 31 and the program 
region 30, and an address signal is pre-recorded in the lead-in region 32. 
The address signal indicates a position on the disc and the value thereof 
is incremented by "1" for every one revolution of the disc 11. It will be 
assumed that an information signal is pre-recorded on information track 
turns in a pre-recorded portion of the program region 30 from starting 
position up to an intermediate position of the program region 30 by a 
previous recording operation. Furthermore, an address signal which 
indicates the track position in time, for example, is pre-recorded 
together with the information signal in this pre-recorded portion of the 
program region 30. A recording frequency or a time position of this 
address signal is selected so that the recording frequency of the address 
signal is different from a recording frequency band of the information 
signal or the time position of the address signal is different from that 
of the information signal. A lead-out region 33 is provided on the outer 
peripheral side of the program region 30. 
The disc 11 is rotated by a motor 12. The information signal and the 
address signal are recorded in the program region 30 of the rotating disc 
11 by a light beam emitted from a pickup device 13, and the recorded 
information signal and the address signal is reproduced from the rotating 
disc 11 by detecting a change in the intensity of a light beam reflected 
by the disc 11. On the other hand, the pre-recorded rotation control 
signal is reproduced from the track 31 by a photo-reflector 14 which 
detects a change in the intensity of light reflected thereby. The detected 
rotation control signal from the photo-reflector 14 is supplied to a 
rotation detecting circuit 15. Since the rotation control signal is 
pre-recorded with a constant period, a rotation detection pulse signal 
having a period inversely proportional to a rotation frequency of the disc 
11 (that is, the motor 12) is obtained from the rotation detecting circuit 
15. 
Description will now be given for the case where the recording of the 
information signal is to be resumed from the intermediate position on the 
disc 11 where the previous recording has been discontinued. The pickup 
device 13 is moved over the pre-recorded portion of the program region 30 
from the lead-in region 32 and stops at a position immediately before an 
end position of the pre-recorded portion. The information signal is a 
frequency modulated signal, for example, and an envelope of a reproduced 
information signal (FM signal) obtained from the pickup device 13 while 
the pickup device 13 (strictly speaking, the light beam) is scanning over 
the pre-recorded portion of the program region 30 has a predetermined 
level, while no envelope is obtained when the pickup device 13 scans over 
an unrecorded portion of the program region 30. Accordingly, when there is 
a large decrease in the level of the envelope detected in an RF detecting 
circuit 28 and a control circuit 18 detects that no envelope is detected 
in the RF detecting circuit 28 for a predetermined time, the pickup device 
13 is returned to a position immediately before the position where the 
level of the envelope largely decreases responsive to a control signal 
which is supplied to a pickup moving mechanism 29 from the control circuit 
18. The pickup device 13 reproduces the signal pre-recorded on the 
information recording track turn at the position immediately before the 
end position of the pre-recorded portion of the program region 30 in a 
stop reproduction mode. A reproduced address signal within the signal 
reproduced by the pickup device 13 is discriminated and separated in an 
address signal detecting circuit 16 and is supplied to an operation 
circuit 17. In the case where the information recording track is a spiral 
track, the pickup device 13 (that is, the light beam) is returned by one 
track pitch for every one revolution of the disc 11 in the stop 
reproduction mode. On the other hand, in the case where the information 
recording track comprises a plurality of concentric tracks, the position 
of the pickup device 13 is maintained the same in the stop reproduction 
mode. 
The reproduced address signal and a signal from the control circuit 18 are 
supplied to the operation circuit 17. The operation circuit 17 calculates 
a present position (radius or distance from a center of the disc 11) of 
the pickup device 13 (or the light beam) based on the value of the 
reproduced address signal and obtains an initial value N of the frequency 
dividing ratio for setting the rotation frequency of the disc 11 to a 
regular value for the present position. This initial value N is supplied 
to a first preset counter 19. 
The relative linear velocity between the pickup device 13 and the disc 11 
can be described by a product of a rotation frequency M and a 
circumference (2.pi.R) at a radius R, where M denotes the rotation 
frequency of the disc 11 (that is, motor 12) when the pickup device 13 is 
at a position of the radius R. Hence, the rotation frequency M is 
inversely proportional to the radius R and the following equation (1) 
stands, where K.sub.1 is a constant. 
EQU M=K.sub.1 /R (1) 
The relationship between the rotation frequency M and the radius R in the 
equation (1) is shown in FIG. 3. In other words, as the pickup device 13 
moves from an inner peripheral position of a radius R.sub.1 to an outer 
peripheral position of a radius R.sub.2, the rotation frequency M 
gradually changes from M.sub.1 to M.sub.2. 
On the other hand, an output signal frequency f.sub.1 of a second preset 
counter 20 which will be described later can be described by f.sub.0 /N, 
where f.sub.0 denotes an output signal frequency of a crystal oscillator 
20 which will be described later and N denotes the frequency dividing 
ratio of the second preset counter 20. Since the rotation frequency M of 
the motor 12 is controlled proportionally to the output signal frequency 
f.sub.1 =f.sub.0 /N of the second preset counter 20, the following 
equation (2) stands, where K.sub.2 is a constant. 
EQU M=K.sub.2 /N (2) 
Hence, the following equation (3) can be derived from the equations (1) and 
(2). 
EQU N=(K.sub.2 /K.sub.1).times.R (3) 
The relationship between the frequency dividing ratio N and the radius R is 
shown in FIG. 4. In other words, as the pickup device 13 moves from the 
inner peripheral position of the radius R.sub.1 to the outer peripheral 
position of the radius R.sub.2, the frequency dividing ratio N linearly 
increases from N.sub.1 to N.sub.2, and the output signal frequency f.sub.1 
of the second preset counter 20 decreases linearly. From the equation (3), 
it can be seen that it is possible to maintain the relative linear 
velocity constant by varying the frequency dividing ratio N proportionally 
to the radius R of the position of the pickup device 13 on the disc 11. 
The first preset counter 19 is an up-counter loaded (preset) with output 
parallel data of the operation circuit 17 which obtains an initial value 
N.sub.1 based on the equation (3) in FIG. 4, for example, when a load 
pulse is received from the control circuit 18. The loaded data (frequency 
dividing ratio) in the first preset counter 19 is supplied to the second 
preset counter 20. The control circuit 18 supplies to a gate circuit 21 a 
gate pulse simultaneously as when the load pulse is supplied to the first 
preset counter 19. The closed gate circuit 21 is opened responsive to the 
gate pulse. The control circuit 18 also supplies a control signal to the 
moving mechanism 29 so that the moving mechanism 29 starts to move the 
pickup device 13 in the outer peripheral direction of the disc 11. When 
the gate circuit 21 is opened, the rotation detection pulse signal from 
the rotation detecting circuit 15 is supplied to a clock input terminal 
CLK of the first preset counter 19. 
The second preset counter 20 is a down-counter which frequency-divides the 
output signal of the crystal oscillator 22 by a frequency dividing ratio N 
which is dependent on the counted value N received from the first preset 
counter 19. The output signal frequency f.sub.0 of the crystal oscillator 
22 is 14 MHz, for example. Accordingly, the output signal frequency 
f.sub.1 of the second preset counter 20 becomes f.sub.0 /N. At first, the 
second preset counter 20 frequency-divides the output signal of the 
crystal oscillator 22 by a frequency dividing ratio (for example, N.sub.1 
shown in FIG. 4) based on the value loaded in the first preset counter 19. 
The output signal of the second preset counter 20 is supplied to a 1/2 
frequency divider 23 and to a load terminal L of the second preset counter 
20. For this reason, the output counted value of the first preset counter 
19 is loaded into the second preset counter 20 for every one period of the 
output signal of the second preset counter 20. Because the first preset 
counter 19 starts to count up the pulses of the rotation detection pulse 
signal after the output signal of the operation circuit 17 is loaded into 
the first preset counter 19, the second preset counter 20 is thereafter 
loaded with the counted value N described by the equation (3) and shown in 
FIG. 4. 
As a result, as the pickup device 13 is moved in the outer peripheral 
direction of the disc 11 at a normal speed, the frequency dividing ratio N 
of the second preset counter 20 increases, and the output signal frequency 
f.sub.1 of the second preset counter 20 gradually decreases. The output 
signal of the second preset counter 20 is frequency-divided by 1/2 in the 
frequency divider 23 having a frequency dividing ratio 2 so as to widen 
the pulse width of the signal, and an output signal of the frequency 
divider 23 is supplied to a phase comparator 24. The phase comparator 24 
compares the phase of the rotation detection pulse signal from the 
rotation detecting circuit 15 and the phase of the output signal of the 
frequency divider 23, and produces a phase error signal which is supplied 
to the motor 12. The rotation of the motor 12 is controlled responsive to 
the phase error signal so as to rotate at the rotation frequency 
proportional to the output signal frequency f.sub.1 of the second preset 
counter 20. Therefore, the rotation frequency M of the motor 12 and the 
disc 11 decreases as the pickup device 13 moves in the outer peripheral 
direction of the disc 11 as shown in FIG. 3, and the relative linear 
velocity between the pickup device 13 and the disc 11 is maintained 
constant to 9.27 m/sec, for example. 
When recording the information signal from the starting position of the 
program region 30, the address signal pre-recorded in the lead-in region 
32 is reproduced. The recording of the information signal is started with 
the preset rotation frequency of 1609.4 rpm, for example, after the 
address value of the reproduced address signal coincides with a known last 
address value in the lead-in region 32. Thereafter, the rotation of the 
motor 12 is controlled similarly as described before so as to gradually 
decrease the rotational speed responsive to the signal which is obtained 
by frequency-dividing the output signal frequency f.sub.0 of the crystal 
oscillator 22 in the second preset counter 20 by a frequency dividing 
ratio based on the output counted value of the first preset counter 19 
which counts the pulses of the rotation detection pulse signal. 
In the case where the information signal comprises video and audio signals, 
the address signal is transmitted within a predetermined interval in a 
vertical blanking period of the video signal, for example, and the address 
signal is recorded in a frequency band different from that of the audio 
signal. The rotation detection pulse signal may be obtained from the disc 
11 by reproducing a signal pre-recorded on a guide track when the disc 11 
has a configuration previously disclosed in a U.S. patent application Ser. 
No. 873,407 filed June 12, 1986 in which the assignee is the same as the 
assignee of the present application. The information signal is recorded on 
the previously proposed disc at an intermediate part between two mutually 
adjacent track turns of the guide track which is pre-formed on the disc, 
and this disc is pre-recorded with a signal having a constant period on 
each of the track turns of the guide track. In addition, it is possible to 
obtain the rotation detection pulse signal by a known frequency generator 
which generates a signal having a frequency dependent on the rotation 
frequency of the motor 12. 
It is also possible to carry out the high-speed search in a reverse 
direction, that is, in the inner peripheral direction of the disc, so as 
to find a starting position of the unrecorded portion within the program 
region 30. In this case, the level of the envelope of the reproduced 
signal is zero when the pickup device 13 is moving and scanning over the 
unrecorded portion within the program region 30, but the level of the 
envelope of the reproduced signal largely increases to the predetermined 
level when the pickup device 13 scans over the pre-recorded portion within 
the program region 30. Hence, the address signal within the reproduced 
signal obtained in the stop reproduction mode when the pickup device 13 is 
at the position where the level of the envelope largely increases to the 
predetermined level is discriminated and separated in the address signal 
detecting circuit 16, and a rotation control similar to that described 
before is carried out so that the pickup device 13 is moved at the normal 
speed in the forward direction (outer peripheral direction of the disc) 
from the starting position of the unrecorded portion within the program 
region 30. 
In the embodiment described heretofore, the disc 11 is an optical disc. 
However, the application of the present invention is not limited to the 
rotation control of the optical disc, and may be applied to the rotation 
control of any type of CLV system disc such as a magnetic disc. 
According to the present invention, an address signal is reproduced from 
the disc, an initial value is set based on a reproduced address signal, 
and a signal to be used for the rotation control is obtained from a 
frequency dividing means which has a frequency dividing ratio varied 
depending on a counted value of rotation detection pulses by starting the 
count from the initial value. According to the rotation control apparatus 
of the present invention, it is possible to carry out the rotation control 
even with respect to a CLV system disc on which the information signal is 
only recorded up to an intermediate position within a program region of 
the disc, so that the information signal can be newly recorded in 
conformance with the CLV system from a position in a vicinity of the 
intermediate position where the previous recording had been discontinued. 
Further, the present invention is not limited to these embodiments, but 
various variations and modifications may be made without departing from 
the scope of the present invention.