Pickup position control method enabling restart of reproduction after interruption

In a method and apparatus of controlling the position of the pickup of a disk player, when the power supply is interrupted during reproduction, data recorded on the disk is read by the pickup held on the prior spot. According to address data in the data thus read, a certain reproduction start position is determined, so that the reproduction is started from that position, whereby the difficulty that the music is reproduced from halfway is prevented.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to a method of controlling the position of a pickup. 
More particularly, the invention relates to a pickup position control 
method for a disk player in which, when the power supply is interrupted 
during reproduction, the pickup is held at the last reading position. 
2. Background of the Prior Art 
Compared with other types of disk players for reproducing signals recorded 
on disk-shaped recording media such as digital audio disks (hereinafter 
referred to merely as "disks"), a mobile disk player or a portable disk 
player has an increased chance that the power supply is interrupted during 
reproduction. When the power supply is interrupted in this manner, a 
problem lies in determining the point on the disk from which the 
reproduction is started again when the electric power is once again 
supplied to the disk player. 
As a solution of the problem, a disk player has been proposed in the art in 
which, when the power supply is interrupted during reproduction, the 
address data of the last reading position is obtained from the data which 
has been read by the pickup prior to interruption of the power supply. 
This address data is stored in a backup memory and the pickup is returned 
to its home position upon power interruption. When the electric power is 
supplied to the disk player again, the address data of the last reading 
position is read out of the backup memory and the pickup is moved to the 
address position thus read out. The reproduction is restarted from that 
position. 
The conventional disk player described above is disadvantageous in that it 
is relatively high in manufacturing cost because it is necessary to use 
the backup memory. 
The use of the backup memory has been eliminated by another disk player in 
which, when the power supply is interrupted during reproduction, the 
pickup is held mechanically at the last reading position. When the 
electric power is supplied to the disk player again, the reproduction is 
started from the last reading position. 
If a disk which is eccentric is played by the disk player in which the 
pickup is held mechanically at the last reading position, then for the 
eccentricity, the spot light (data reading point) of the pickup is driven 
radially of the disk by the actuator of the pickup to follow a 
predetermined track. However, if the power supply is interrupted during 
the track following operation, the actuator is returned to the neutral 
position, as a result of which a difference corresponding to the 
eccentricity can exist between the position where the pickup is 
mechanically held and the last reading position of the spot light. In 
other words, if the disk is eccentric, then the accuracy of holding the 
pickup in place is substantially limited by the eccentricity of the disk. 
According to the disk standard, the eccentricity of a disk is .+-.0.2 mm, 
which is about 27 to 77 sec. in terms of reproduction address time. 
Because of this great fluctuation, when the electric power is supplied to 
the disk player after the interruption of the power supply, the 
reproduction cannot be started from the last reading position. 
Furthermore, a problem occurs, not only in the disk player of the type that 
the address data of the last reading position is stored in the backup 
memory but also in the disk player of the type that the pickup is held 
mechanically at the last reading position. When the electric power is 
supplied to the disk player again, the reproduction is started from the 
last reading position, i.e., the music is reproduced a second time from 
the last reading position. Therefore, the person perceives the reproduced 
music to be unnatural. 
SUMMARY OF THE INVENTION 
Accordingly, an object of this invention is to provide a pickup position 
control method which eliminates the above-described difficulties 
accompanying a conventional disk player in which, when the power supply is 
interruption during reproduction, the pickup is held at the last reading 
position. 
The foregoing object and other objects of the invention have been achieved 
by the provision of a pickup position control method for a disk player. In 
this method, when the power supply is interrupted during reproduction, the 
pickup for reading data recorded on a disk-shaped recording medium is held 
at the last reading position. According to the invention, data recorded on 
the disk-shaped recording medium is read by the pickup on the previously 
held spot when the power supply is resupplied to the disk player. 
According to read address data in the data thus read, predetermined 
address data in one and the same group of data to which the read address 
data belong is employed as target address data. According to the address 
difference between the target address data and the read address data, the 
pickup is moved to the position of the predetermined address data, so that 
. reproduction is started from that position. 
The nature, principle and utility of the invention will become more 
apparent from the following detailed description when read in conjunction 
with the accompanying drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
A disk reproducing device (hereinafter referred to as "a disk player"), to 
which a pickup position control method according to this invention is 
applied, is shown in FIG. 1. A pickup 2 for reading data recorded on a 
disk 1 is threadably engaged with a threaded shaft 3 which extends 
radially with respect to the disk. As a result, the pickup 2 is moved 
along the threaded shaft 3 and accordingly moves radially of the disk as 
the threaded shaft 3 is rotated by an electric motor 4. 
The output signal of the pickup 2 is applied, as a read RF (radio 
frequency) signal, through an RF amplifier 5 to a demodulating circuit 6, 
where it is demodulated. The output signal of the demodulating circuit is 
supplied to a signal reproducing system and to a data extracting circuit 
7. In the data extracting circuit 7, address data are extracted from the 
demodulated output of the demodulating circuit 6. The address data are 
applied to a controller 8 comprising a microcomputer or the like. In the 
case of a digital audio disk, the address data are stored in a table of 
contents (TOC) in a disk directory portion of the disk, as referred to in 
step S10 of FIG. 2 which describes, among other things, a search 
operation. The address data are stored in the form of a track number 
(music number), an index umber in a piece of music, and a period of time 
passed for music performance (minutes and seconds) (hereinafter referred 
to as "a prior music performance time") in a sub-code Q-channel signal. 
The controller 8 drives the motor 4 through a motor drive circuit 9 to 
control the position of the pickup 2 in the radial direction of disk. 
The pickup 2 accommodates a focus servo mechanism for maintaining the 
distance between an objective lens in the pickup 2 and the data recording 
surface of the disk 1 constant. The pickup also contains a tracking servo 
mechanism for causing the spot light of the pickup 2 to correctly follow 
the data-recorded track. Furthermore, the control of the disk player is so 
designed that, when the power supply is interrupted during reproduction, 
the pickup 2 is no longer driven and it is mechanically held at the last 
reading position. 
The pickup position control method of the invention which is practiced by 
the controller 8 will be described with reference to a flow chart in FIG. 
2. 
When the power supply to the disk player is turned on, whether after an 
interruption or in normal turning-on, first a focus servo operation and a 
tracking servo operation are carried out (Step 1), and then the data 
recorded on the disk 1 are read (Step 2). When the power supply is 
resupplied to the disk player again after having been interrupted, the 
pickup 2 is mechanically held at the last reading position to which the 
pickup was moved just prior to the interruption of the power supply 
because no move commands have issued to the motor driving circuit 9. 
Therefore, in the case of a power interruption, the read data can be 
obtained. On the other hand, when the power supply is supplied to the disk 
player for the first time after the disk has been set on the disk player, 
no read data can be obtained, because the pickup 2 is at the home 
position. As is apparent from the above description, it can be determined 
from the presence or absence of the read data whether the electric power 
has been supplied to the disk player after an interruption or for the 
first time. This determination is carried out in Step 3. 
When, in Step 3, it is determined that the read data is available, i.e., 
the power has been resupplied to the disk player after an interruption, 
the address data are extracted from the read data (Step 4), so that the 
track number (music number) and the prior music performance time (XX track 
YY min. ZZ sec.) at the position where the pickup has been held are 
obtained, as read address data, from the address data thus extracted. 
Then, address data for starting reproduction is obtained, for instance as 
the top address data (XX track, 00 min. 00 sec.) of the track (the group 
data of a piece of music) to which the read address data belong, and the 
starting address data is set as the target address data (Step 5). The 
target address data is the address to be searched for. Therefore, the 
address difference between the target address data and the read address 
data is calculated (Step 6), and a direction and the number of tracks for 
movement of the pickup are obtained from the address difference thus 
calculated (Step 7). Then, the pickup 2 is moved in the direction while 
the number of tracks crossed by the pickup are being counted, so that the 
position of the target address data is searched (Step 8), and the 
reproduction is started from the position thus searched. 
If, in Step 3, it is determined that the read data is not available, i.e., 
the power supply is supplied to the disk player for the first time after 
the disk has been set on the disk player, then the pickup 2 is moved to a 
lead-in area, where the disk directory data is read (Step 10), and then 
the reproduction is started (Step 11). 
In the above-described embodiment, according to the read address data, the 
address data of the top of the track (the top of the music) to which the 
read address data belong is employed as the target address data. However, 
the invention is not limited thereto or thereby. For instance, the address 
data of a transition position expressed in minutes (XX track, YY min. 00 
sec) or the address data of a transition point between phrases in a piece 
of music) may be employed as the target address data. 
The controller 8 carries out search control, random access control, etc. 
similarly as in a controller (host microcomputer) in Japanese Patent 
Application (OPI) NO. 229278/1985 (the term "OPI" as used herein means "an 
unexamined published application"). 
As described in that application, information recorded on the disc 1 (FIG. 
1) contains program data including address data, and is read by the pickup 
2. The information is demodulated by the demodulator 6 as described above, 
and is supplied to an address detector 8a, which detects address 
information and the current position of the pickup 2. The latest address 
data then is loaded into an address memory 8b of the 
controller/microcomputer 8. The microcomputer 8 also includes an address 
counter 8c which counts address data at predetermined time intervals 
during disk playback, and sequentially produces an output signal 
indicative of the expected address to which the pickup 2 should be moved 
next. 
The address detector 8a compares the information in the address memory 8b 
and the expected address information in the counter 8c. Depending on the 
discrepancy (if there is one), the controller 8 may determine that it 
needs to move farther to get to the target track, or that it has overshot 
the target track, and so needs to move the pickup 2 back. 
In executing search control, there are two situations to consider. First, 
in a case in which the recorded information on the disk is to be played in 
sequence, after the table of contents (TOC) section is read, the pickup 
would be sent to the first location at which there is information which is 
to be reproduced, and reproduction would be started from there. 
If it is desired to start reproduction at another, user-designated point on 
the disk (as in the case of random access control, for example), the TOC 
holding the address data in the lead-in area of the disk would be read to 
determine a target address. The target address then would be searched to 
find the starting point, at which point reproduction then could be 
started, in a manner similar to steps S4-S9 in FIG. 2. The position of the 
pickup 2 during this search is determined by comparing the present address 
with the target address, and moving the pickup 2 forward (if the target 
address is greater than the present address) or backward (if the target 
address is less than the present address). Backward movement may occur 
more often during random access control, since the playback sequence, 
instead of being 1-2-3-4 . . . (as would be normal) might be 4-2-3-1 . . . 
instead. 
Depending on the distance the pickup 2 must travel to reach the target 
address, the pitch of stepwise movement of the pickup 2 may be altered. 
For a relatively great distance for the pickup 2 to travel, the pitch may 
be greater than for a relatively small distance to be travelled. This 
variation of pitch prevents the pickup from being moved in improperly 
large steps. 
As was described above, in the disk player in which, when the power supply 
is interrupted during reproduction, the pickup is held at the last reading 
position. According to the pickup position control method of the 
invention, the reproduction start address data is determined from the read 
address data obtained from the read data which is obtained at the position 
where the pickup is located when the power is resupplied to the disk 
player so that the reproduction is started from the predetermined address 
data position. Therefore, even if the read data fluctuates greatly, as 
much as about twenty-seven to seventy-seven seconds, the reproduction is 
started, irrespective of the fluctuation, from the position which has been 
finally read. Therefore, the above-described difficulty that, when the 
power supply is made to the conventional disk player again after having 
been interrupted, the reproduction of unnaturally sounding music can be 
eliminated according to the invention.