Optical disc drive apparatus

A reproducing apparatus includes access means for accessing a recording medium so that an information signal is read out from the recording medium, detecting means for counting frequency with which the access means accesses the same recording unit region of the recording medium and detecting a recording unit region of high access frequency, random number generating means for generating a random number, and moving means for moving the access means to other recording unit region on the recording medium in response to a random number generated from the random number generating means after the access means accesses the recording unit region of high access frequency detected by the detecting means.

BACKGROUND OF THE INVENTION 
The present invention relates to an optical disc drive apparatus and, more 
particularly, is directed to an optical disc drive apparatus for use with 
a recording and reproducing apparatus using a phase-change type optical 
disc as a recording medium. 
A recording and reproducing apparatus for recording and reproducing 
information signal with radiation of laser beams uses a disk-shaped 
recording medium (simply referred to hereinafter as "optical disc"). Such 
recording medium might be a read-only optical disc, a write-once optical 
disc in which an information signal can be written once and an optical 
disc using a magneto-optical recording medium in and from which an 
information signal can be recorded and erased a plurality of times. 
The read-only optical disc includes a track on which uneven patterns, i.e., 
pits are formed concentrically or spirally formed on one surface thereof. 
Specifically, this optical disc is composed of a disc substrate made of a 
transparent synthetic material, such as polycarbonate, PMMA {poly (methyl 
methacrylate)} or the like, a reflection film made of a metal such as Al 
or Au so as to cover phase pits formed on one surface of the disc 
substrate and a protection film formed so as to cover the reflection film 
in order to protect the reflection film. 
As the write-once optical disc, there is proposed a phase-change type 
optical disc which can form pits with high density. The phase-change type 
optical disc is composed of a transparent substrate in which pits are 
formed on the surface and a phase-change film formed on the transparent 
substrate. The phase-change film is at least one selected from Sb.sub.2 
Se.sub.3, Sb.sub.2 Te.sub.3, Se, Te, BiTe, BiSe, In-Se, In-Sb-Te, In-SbSe, 
In-Se-Tb.sub.1, Ge-Te-Sb and Ge-Te. 
A magneto-optical disc using a vertical magnetic recording medium or the 
like is known as a recordable optical disc. 
This magneto-optical disc is composed of a disc substrate in which guide 
grooves for guiding laser beam are formed on one surface and which is made 
of a transparent synthetic resin such as polycarbonate, PMMA or the like, 
a recording layer made of a vertical magnetic recording material, such as 
Te, Fe, Co or the like, the recording layer being formed so as to cover 
the guide grooves, and a protection layer formed so as to cover the 
recording layer in order to protect the protecting layer. 
A method of reproducing these optical discs will be described below. When 
the read-only optical disc and the write-once optical disc are reproduced, 
laser beam from a laser light source is radiated on the optical disc 
substrate under the condition that the laser beam is converged by an 
objective lens. Reflected light flux that was modulated by phase pits of 
the optical disc is detected by a photodetector, for example, and a 
reproduced signal of the information signal recorded on the optical disc 
is obtained by obtaining a detected signal having signal level 
corresponding to intensity of the reflected light flux. 
When the latter recordable optical disc is reproduced, similarly to the 
read-only optical disc, laser beam from the laser light source is radiated 
on the disc substrate under the condition that the laser beam is converged 
by the objective lens. Then, a reproduced signal of the information signal 
recorded on the magneto-optical disc is reproduced by detecting a Kerr 
rotational angle in the reflected light flux modulated by the recording 
layer of the optical disc. 
However, in the recording and reproducing apparatus, if data on the same 
track is periodically accessed at a cycle within a predetermined time, 
then it is frequently observed that the optical head is not returned to 
the home position so that the optical head stays on the same track. In 
this case, reproducing laser beam emitted from the optical head is 
radiated on the same track for a long period of time with the result that 
the track portion radiated by the reproducing laser beam is locally 
heated. There is then the risk that the optical disc itself is deformed by 
heat. 
To solve the aforementioned problem, it is proposed to reduce a time 
("predetermined time") in which the optical head is stopped on the same 
time. However, according to this proposed method, a frequency with which 
the optical head is moved to the home position is increased. There is then 
the risk that access efficiency is lowered. 
Relationship between the frequency in which the optical head is moved to 
the home position and the efficiency in which the optical head accesses 
data is so-called trade-off relationship. Accordingly, it is not possible 
to satisfy both of the frequency and the access efficiency in response to 
all sorts of manners in which the recording and reproducing apparatus and 
the optical disc are in use. 
OBJECTS AND SUMMARY OF THE INVENTION 
It is therefore an object of the present invention to provide a recording 
and reproducing apparatus in which it is possible to avoid in advance an 
access head from being stopped at the same position for a long period of 
time. 
Another object of the present invention is to provide a recording and 
reproducing apparatus in which an access speed can be increased. 
Still another object of the present invention is to provide a recording and 
reproducing apparatus in which it is possible to prevent in advance heat 
from being accumulated in an optical disc when reproducing laser beam 
radiates the same position of the optical disc for a long period of time 
if the present invention is applied to an apparatus for recording and 
reproducing a phase-change type optical disc. 
A further object of the present invention is to provide a recording and 
reproducing apparatus in which a phase-change type optical disc can be 
accessed at high speed. 
According to a first aspect of the present invention, there is provided a 
reproducing apparatus which is comprised of access means for accessing a 
recording medium so that an information signal is read out from the 
recording medium, detecting means for counting frequency with which the 
access means accesses the same recording unit region of the recording 
medium and detecting a recording unit region of high access frequency, 
random number generating means for generating a random number, and moving 
means for moving the access means to other recording unit region on the 
recording medium in response to a random number generated from the random 
number generating means after the access means accesses the recording unit 
region of high access frequency detected by the detecting means. 
According to a second aspect of the present invention, there is provided a 
recording apparatus which is comprised of access means for accessing a 
recording medium so that an information signal is read out from the 
recording medium, detecting means for counting frequency with which the 
access means accesses the same recording unit region of the recording 
medium and detecting a recording unit region of high access frequency, 
random number generating means for generating a random number, and moving 
means for moving the access means to other recording unit region on the 
recording medium in response to a random number generated from the random 
number generating means after the access means accesses the recording unit 
region of high access frequency detected by the detecting means. 
According to a third aspect of the present invention, there is provided a 
reproducing apparatus which is comprised of access means for accessing a 
recording medium so that an information signal is read out from the 
recording medium, detecting means for counting frequency with which the 
access means accesses the same recording unit region of the recording 
medium and detecting a recording unit region of high access frequency, and 
moving means for sequentially moving the access means within a recording 
unit region near recording unit region of high access frequency on the 
recording medium after the access means accesses the recording unit region 
of high access frequency detected by the detecting means. 
In accordance with a fourth aspect of the present invention, there is 
provided a recording apparatus which is comprised of access means for 
accessing a recording medium so that an information signal is read out 
from the recording medium, detecting means for counting frequency with 
which the access means accesses the same recording unit region of the 
recording medium and detecting a recording unit region of high access 
frequency, and moving means for sequentially moving the access means 
within a recording unit region near recording unit region of high access 
frequency on the recording medium after the access means accesses the 
recording unit region of high access frequency detected by the detecting 
means. 
In accordance with a fifth aspect of the present invention, there is 
provided an access method of accessing a recording medium by access means. 
The access method is comprised of the steps of (a) counting frequency with 
which the same recording unit region of a recording medium is accessed by 
access means and detecting a recording unit region of high access 
frequency, (b) detecting whether or not the recording unit region of high 
access frequency detected at step (a) is accessed by the access means, (c) 
generating a random number, and (d) moving the access means to other 
recording unit region on the recording medium in response to the random 
numbers after the recording unit region of high access frequency detected 
by the step (a) is accessed by the access means. 
In accordance with a sixth aspect of the present invention, there is 
provided an access method of accessing a recording medium by access means. 
The access method is comprised of the steps of (a) counting frequency with 
which the same recording unit region of a recording medium is accessed by 
access means and detecting a recording unit region of high access 
frequency, (b) detecting whether or not the recording unit region of high 
access frequency detected at step (a) is accessed by the access means, and 
(c) sequentially moving the access means within a recording unit region 
near the recording unit region of high access frequency on the recording 
medium after the recording unit region of high access frequency detected 
by the step (a) is accessed by the access means. 
The above, and other objects, features, and advantages of the present 
invention will become apparent from the following detailed description of 
preferred embodiments thereof to be taken in conjunction with the 
accompanying drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
A recording and reproducing apparatus according to the present invention 
will be described below with reference to FIGS. 1 through 11. In this 
embodiment, the recording and reproducing apparatus is applied to a 
recording and reproducing apparatus using a write-once phase-change type 
optical disc as a recording medium. This recording and reproducing 
apparatus will be referred to hereinafter as "inventive recording and 
reproducing apparatus" for simplicity. 
As shown in FIG. 1, the inventive recording and reproducing apparatus 
includes a turntable 2 on which a phase-change type optical disc (simply 
referred to hereinafter as "optical disc") 2 is loaded, a spindle motor 
(M) 3 for rotating the optical disc 1 loaded on the turntable 2 in a 
predetermined direction in a CLV (constant linear velocity) fashion or in 
a CAV (constant angular velocity) fashion, an optical head 4 for accessing 
(recording and reproducing) an information signal to the rotating optical 
disc 1 and a signal processor 5 for demodulating the reproduced data 
supplied thereto from the optical head 4 to supply reproduced data to the 
outside and also modulating writing data supplied thereto from the outside 
to supply a writing signal to the optical head 4. 
As shown in FIG. 2, the optical disc 1 includes a system region a provided 
on its inner peripheral portion to record data concerning attribute of the 
optical disc 1, such as rotation control system, i.e., CLV system, CAV 
system, and track pitch and the number of tracks, i.e., TOC (table of 
contents) data not as a phase-change material layer but as pit information 
based on concavities and convexities similarly to the compact disc (CD) 
and a user region b formed by the phase-change layer except the system 
region a in which the TOC data is recorded. 
The optical head 4 can be moved in the diameter direction of the optical 
disc 1 by an optical head slide mechanism 11 composed of mainly a linear 
motor and a guide shaft, not shown, for example. The optical head 4 
includes at least a semiconductor laser (not shown) disposed therein to 
serve as a light source for emitting laser beam, an objective lens 12 for 
converging laser beam L emitted from the semiconductor laser on the 
phase-change material layer (recording layer) of the optical disc 1, a 
photodetector (not shown) for detecting a reflected-back light obtained 
after the laser beam L emitted from the semiconductor laser was reflected 
on the optical disc 1 and converting the reflected-back light into an 
electrical signal and a beam splitter (not shown) for spatially splitting 
the reflected-back light and the light emitted from the semiconductor 
laser. 
The objective lens 12 of the optical head 4 can be moved by a 
two-dimensional actuator 13 of a simple structure in very small ranges in 
the direction perpendicular to the optical disc 1 and the diameter 
direction of the optical disc 1. The two-dimensional actuator 13 includes 
magnetic circuit composed of a focusing coil, a tracking coil and a 
magnetic, for example, though not shown. 
A signal processor 5 comprises a playback RF amplifier (RF AMP) 21 for 
amplifying a reproduced signal from the photodetector in the optical head 
4, a demodulator (DEMOD) 22 for demodulating a reproduced amplified signal 
from the RF amplifier 21 and converting a demodulated reproduced amplified 
signal to digital reproduced data by decoding, such as error correction or 
the like, a modulator (MOD) 23 for modulating recording data supplied 
thereto from the outside in suitable modulation, such as an EFM 
(eight-to-fourteen modulation) or the like and converting modulated 
recording data to a binary signal serving as pit recording information, a 
servo controller (SERVO CONT) 24 for servo-controlling the spindle motor 
3, the two-dimensional actuator 13 and the optical head slide mechanism 11 
by servo signals and a system controller (SYSTEM CONT) 25 for controlling 
each of the above-mentioned elements in various manners. The signal 
processor 5 includes a laser beam controller (APC) 26 for controlling 
intensity of laser beam emitted from the semiconductor laser in the 
optical head 4. 
There are prepared the 7 inventive sub-systems C at maximum. Each of the 
sub-system C includes a recording and reproducing apparatus A with an 
interface bus controller and a recording and reproducing apparatus B with 
a local bus. The recording and reproducing apparatus A can be connected 
with 7 recording and reproducing apparatus B at maximum. Specifically, the 
recording and reproducing apparatus A and a plurality of recording and 
reproducing apparatus B disposed under the recording and reproducing 
apparatus A constitute one sub-system C. The recording and reproducing 
apparatus system is arranged such that the sub-system C composed of a 
plurality of recording and reproducing apparatus is electrically connected 
through an interface bus (e.g., SCSI: small computer systems interface) 31 
to a host computer 32 which monitors and controls a plurality of 
sub-systems C. 
As shown in FIG. 3, an interface command controller 43 includes a detecting 
means (DET MEANS) 44 composed of a program memory 33 in which various 
programs are registered, an operation RAM (random access memory) 34 used 
as an operation region of program read out from the program memory 33 and 
which is also used as a storage region for storing data table (file) thus 
made, a calculating unit 35 for processing and identifying data in 
accordance with an algorithm of the program stored in the operation RAM 34 
and a control unit 36 for controlling the program memory 33, the operation 
RAM 34 and the calculating unit 35. 
Operations and signal processings of the recording and reproducing 
apparatus system and the respective recording and reproducing apparatus 
will be described below under the assumption that a set of sub-system 
composed of 8 recording and reproducing apparatus is connected to the host 
computer 32 and that optical disc 1 is loaded on each of the recording and 
reproducing apparatus. 
Initially, in each of the recording and reproducing apparatus, the optical 
head 4 reads out TOC data recorded on the system region a (see FIG. 2) of 
the optical disc 1. The system controller 25 detects on the basis of the 
read-out TOC data whether the format of the optical disc 1 is the format 
of the CLV system or the format of the CAV system. Then, the system 
controller 25 supplies an information signal of each corresponding 
rotational system to the servo controller 24. 
The servo controller 24 generates a servo signal based on the information 
signal supplied thereto from the system controller 25 and a timing signal 
concerning rotational speed supplied thereto from the spindle motor 3 and 
supplies the servo signal thus generated to the spindle motor 3. The 
spindle motor 3 is driven under the control of the servo signal supplied 
thereto from the servo controller 24 so that the optical disc 1 can be 
rotated stably in a CLV or CAV system fashion. 
To write an information signal in the optical disc 1 in a write-once 
fashion from this state will be described below. Data stored in the 
operation RAM provided within the host computer 32, for example, is 
supplied through the interface bus 31 to a write target recording and 
reproducing apparatus. 
In this embodiment, to select a write target recording and reproducing 
apparatus, the host computer 32, for example, outputs a write request 
signal through the interface bus 31 connected to the 8 recording and 
reproducing apparatus to the write target recording and reproducing 
apparatus. Further, the host computer 32 transmits selection data in which 
device Nos. corresponding to the respective recording and reproducing 
apparatus are inserted into the starting portion of control data as a code 
to the write target recording and reproducing apparatus. The interface 
command controller 43 reads out this code and transmits the code thus read 
out through the system controller 25 and a device local bus 45 to the 
respective system controllers 25 one more time. The respective system 
controllers 25 verify the code and the device Nos. assigned to the 
respective recording and reproducing apparatus, and only the recording and 
reproducing apparatus whose device No. is agreed with the code can be 
supplied with write data supplied thereto through the system controller 25 
from the host computer 32. 
The write target recording and reproducing apparatus thus selected supplies 
the data supplied thereto from the host computer 32 through the interface 
command controller 43 and the system controller 25 to the modulator 23. At 
that time, the system controller 25 outputs a control signal used to set a 
recording laser output intensity to the laser beam controller (APC) 26. 
The laser beam controller 26 responds to the control signal input thereto 
from the system controller 25 to change comparison reference level of 
laser output to recording output level so that the laser output intensity 
can be stabilized to the recording output intensity. 
The system controller 25 generates a signal representing a moving amount of 
the optical head 4 based on track address data of the data supplied 
thereto and supplies this signal to the optical head slide mechanism 11. 
The optical head slide mechanism 11 responds to the signal representing 
the moving amount of the optical head 4 input thereto to move and place 
the optical head 4 to a corresponding track. Then, the optical head 4 
records the data supplied thereto from the host computer 32 on the 
corresponding track. 
The optical head 4 sequentially records write data sequentially supplied 
thereto from the host computer 32 on the corresponding tracks of the 
corresponding optical discs 1. The write data thus sent from the host 
computer 32 are data that the user makes by the host computer 32 or data 
that the user makes by the host computer 32 on the basis of external 
source data. These write data are recorded on the user regions b (see FIG. 
2) of the optical discs 1. The data recorded on the user regions b of the 
optical discs 1 are used as an extended ROM (read-only memory) of the host 
computer 32. Specifically, each of the recording and reproducing apparatus 
is used as an auxiliary memory apparatus (extended ROM) of the host 
computer 32. 
As specific examples of data recorded on the respective optical discs 1, 
there might be enumerated background picture data, character data or 
dictionary data displayed on a CRT (cathode ray tube) when game software 
or software for word processing is operated. 
Operation and signal processing for reproducing the optical disc 1 in which 
data is recorded in a write-once fashion will be described next. Prior to 
reading data, the system controller 25 outputs the control signal to the 
laser beam controller 26 so that the laser beam controller 26 may set 
intensity of reproducing laser output. The laser beam controller 26 
responds to the control signal supplied thereto from the system controller 
25 to change comparison reference level of laser output to reproducing 
output level so that the laser output is stabilized to the reproducing 
output. 
When the user executes the game software or the software for word 
processing by input means 41, such as a keyboard or the like connected to 
the host computer 32, for example, in the detecting means 44 provided 
within the interface command controller 43, a program for actuating 
various software is stored in the operation RAM 34 from the program memory 
33 through the control unit 36 and the program is executed from its start 
address via the calculating unit 35. 
During this program is executed, a read-out request command for reading out 
the extended ROM data is issued and a data read-out request command is 
supplied to the corresponding recording and reproducing apparatus through 
an operation system (OS). This request is executed by supplying data 
composed of a data read-out request command, the device No. of the 
recording and reproducing apparatus and the read-out address through the 
interface bus 31 to 8 recording and reproducing apparatus. 
When this read-out request is executed, time data representing 3 seconds is 
set to a counter (not shown) provided within the system controller 25 at 
the stage that a data readout command is supplied to a read target 
recording and reproducing apparatus. This counter subtracts time data 
based a clock signal input thereto from a timer 42, and outputs a reset 
signal to a control unit (not shown) of the system controller 25 when time 
data becomes zero. The control unit of the system controller 25 outputs a 
control signal concerning movement of the optical head 4 to the servo 
controller 24 based on the reset signal input thereto from the counter. 
The servo controller 24 responds to the control signal input thereto from 
the system controller 25 to output a servo signal to the optical head 
slide mechanism 11 so that the optical head 4 is moved to the home 
position, e.g., region c shown hatched in FIG. 2, such as a track used as 
a spare space for data concerning defect management of a predetermined 
track of the system region a on which TOC data, for example, is recorded. 
Specifically, the region that is not the recording region of user data or 
the like us set as the home position c. However, such region should 
preferably be an region in which address data is recorded so that the next 
accessing can be carried out readily. The optical head slide mechanism 11 
moves the optical head to the home position c based on the servo signal 
input thereto from the system controller 25. 
According to a series of the above operation, the optical head is moved to 
the home position c if the next accessing is not made even after 3 seconds 
are elapsed from the previous access (read-out request). If the next 
accessing is made within 3 seconds from the previous accessing, the 
optical head 4 is not moved to the home position c but is moved onto the 
track to be accessed. Moreover, each time the accessing is requested, time 
data representing 3 seconds is registered in the counter provided within 
the system controller 25. 
According to this embodiment, an access frequency counting program is read 
out from the program memory in accordance with the extended ROM data 
read-out request. This access frequency counting program thus read out is 
stored in the operation RAM 34 through the control unit 36 and executed. 
A processing routine for processing the access frequency counting program 
will be described with reference to flowcharts of FIGS. 4 to 7 and various 
information tables of FIGS. 8A through 8D. 
When this access frequency counting program is executed, two data table, 
one count file, one FIFO (first-in first-out) system latch region and one 
frequency detection flag are logically allocated to a predetermined array 
variable region (region used to store data) in the operation RAM 34. 
A first data table is an access frequency counting table: ACS and 
composed of 8 files (ACSFIL#0 to ACSFIL#7) in response to the 8 recording 
and reproducing apparatus as shown in FIG. 8A. Each file is composed of 64 
records (ACSRCD#0 to ACSRCD#63), and each record is formed of 4 bytes. 
Each record ACSRD is composed of access number data CNT stored in the 
first 1 byte and track address data LBA stored in remaining 3 bytes. The 
access frequency counting table (ACS) has a recording capacity of 8 
files.times.64 records.times.4 bytes=2048 bytes. 
A second table data is a maximum access information table: MAX and 
composed of 8 records (MAXRCD#0 to MAXRCD#7) in response to the 8 
recording and reproducing apparatus as shown in FIG. 8B. Each record 
MAXRCD is formed of 4 bytes similarly to each record ACSRCD of the access 
frequency counting table (ACS). Each record MAXRCD is composed of 
access number data CNT stored in the first 1 byte and track address data 
LBA stored in remaining 3 bytes. The maximum access information table 
(MAX) has a recording capacity of 8 records.times.4 bytes=32 bytes. 
A count file is a data file: TTLCNT to count the number of access and 
composed of 8 records (TTLRCD#0 to TTLCNT#7) in response to the 8 
recording and reproducing apparatus as shown in FIG. 8C. Each record 
TTLCNT is composed of 1 byte and used to update the access number data 
CNT. Therefore, the count file (TTLCNT) has a recording capacity of 8 
bytes. 
In the latch region of the FIFO system, there are sequentially stored a 
pair of data composed of device No. DNO and track address data LBA which 
are requested in read by a program with priority higher than that of the 
access frequency counting program, though not shown. The device No. DNO 
and the track address data LBA stored in the latch region are shifted up 
to the start address each time the program is executed and used to 
identify the device No. DNO and the track address LBA. 
A frequency detection flag: ACSFLG is formed of 1 byte which are assigned 
to the 8 recording and reproducing apparatus bit by bit as shown in FIG. 
8D. High "1" level represents a registered track address with maximum 
access frequency and low "0" level represents unregistered track address 
of maximum access frequency. 
The access frequency counting program is successively activated after the 
host computer 32 accesses each recording and reproducing apparatus and 
reads out data from the read request address of the optical disc 1 in the 
recording and reproducing apparatus corresponding to a read target device 
No. DNO. 
The processing order of this program will be described. As shown in the 
flowcharts (main routines) of FIGS. 4 to 6, initially, the read target 
device No. DNO and the track address data LBA are read out from the start 
address of the latch region and set to first and second index registers 
R1, R2 defined on the program in step S1. The processing proceeds to the 
next step S2, wherein an initial value (zero (0)) is stored in a third 
index register R3 defined on the program and in which the point number is 
stored. 
Then, the processing proceeds to step S3, whereat the file ACSFIL 
corresponding to the device No. DNO is selected from the access frequency 
counting table (ACS) by using the device No. stored in the first index 
register R1 as an index. Thereafter, the processing proceeds to step S4, 
whereat the record ACSRCD corresponding to the point number is selected 
from the corresponding file by using the point number stored in the third 
index register R3 as an index. 
It is determined in decision step S5 whether or not the selected record 
ACSRCD has registered data. This identification is made based on the 
numerical value of the start byte of the selected record ACSRCD, i.e., 
whether the access number data CNT is 0 or not. If the access number data 
CNT is not 0, i.e., the selected record ACSRCD has the registered data as 
represented by a YES at decision step S5, then the processing proceeds to 
the next decision step S6. Because the record ACSRCD is registered from 
MAXRCD=0, it is possible to determine only by the numerical value of the 
start byte of the selected record ASCRCD whether the selected record 
ACSRCD has the registered data or not. 
It is determined in decision step S6 whether or not the track address data 
LBA stored in the second index register R2 and the track address data LBA 
registered on the selected record ACSRCD are agreed with each other. If 
they are not agreed with each other as represented by a NO at decision 
step S6, then the processing proceeds to the next step S7, whereat the 
point number stored in the third index register R3 is updated by addition 
of 1. 
It is determined in decision step S8 whether or not the confirmation of 
registered data on all records ACSRCD concerning the selected file ACSFIL 
is finished. This identification is carried out by determining whether or 
not the point number stored in the third index register R3 becomes 64. If 
the point number is not reached to 64 as represented by a NO at decision 
step S8, then the processing returns to step S4, whereat the record ACSRCD 
corresponding to the updated point number is selected. Then, the step S5 
and the following steps are executed. 
If the selected record ACSRCD has no registered data as represented by a NO 
at decision step S5, then the processing proceeds to decision step S9 
shown in FIG. 5, whereat it is determined whether or not the point number 
within the third index register R3 is equal to 0 ((R3)=0). If the point 
number is zero as represented by a YES at decision step S9, this means 
that all records ACSRCD in the selected file ACSFIL have no registered 
data. Then, the processing proceeds to the next step S10. In this case, 
since data is registered in the file ACSFIL from the record ACSRCD#0, if 
R3 is "0", then all records ACSRCD have no registered data. 
In step S10, a record corresponding to the device NO. DNO is selected from 
the maximum access information table MAX by using the device No. DNO 
within the first index register R1 as an index. Then, it is determined in 
the next decision step S11 whether or not the content of the first byte of 
the selected record is zero. If it is zero as represented by a YES at 
decision step S11, the read target recording and reproducing apparatus 
determines that the track address of the maximum access number is not 
determined at all. Then, the processing proceeds to step S12, whereat a 
corresponding bit (i.e., bit corresponding to the device No. DNO) of the 
frequency detection flag (ACSFLG) is reset. 
In the next step S13, read request track address data LBA stored in the 
second index register R2 is registered in the record ACSRCD selected from 
the access frequency counting table (ACS). Thereafter, in step S14, "1" 
is registered in the start byte of the record ACSRCD as access number data 
CNT. 
If on the other hand the number of points is not zero as represented by a 
NO at decision step S9, then the track address data LBA in the selected 
registered record ACSRCD and the read request track address data not 
agreed with each other but there exists the record having no registered 
data. In this case, the processing proceeds to step S13 and the following 
steps are repeated, wherein the read request track address data LBA stored 
in the second index register R2 is registered in the selected record 
ACSRCD, whereafter "1" is registered in the start byte of the record 
ACSRCD as the access number data CNT. 
In FIG. 4, it is determined in decision step S6 whether or not the track 
address data LBA stored in the second index register R2 and the track 
address data LBA registered in the selected record ACSRCD are the same. If 
a YES is output at decision step S6, then the processing proceeds to step 
S15, whereat the count number data CNT within the start byte in the 
selected record ACSRCD is updated by adding "1" thereto. 
After step S14 or S15 is ended, the processing proceeds to step S16, 
whereat a record TTLRCD corresponding to the device No. DNO is selected 
from the count file TTLCNT by using the device NO. DNO stored in the first 
index register R1 as an index. Thereafter, the processing proceeds to step 
S17, whereat the access number CNT within the selected record TTLRCD is 
updated by addition of "1". 
It is determined in the next decision step S18 whether or not access for 
the recording and reproducing apparatus corresponding to the corresponding 
device No. DNO 64 times is finished. This decision is made by determining 
whether or not the value within the record TTLRCD selected at step S16 is 
64 or greater. If this value is 64 or greater as represented by a YES at 
decision step S18, then the processing proceeds to step S19, whereat the 
processing enters the maximum access frequency detection subroutine. 
In the maximum access frequency detection subroutine, as shown in FIG. 7, 
in step S101, an initial value=0 is set to the fourth index register R4 
defined on the program as the index point number. Further, in step S102, 
an initial value=0 is set to the maximum value register MAXR similarly 
defined on the program. The maximum value register MAXY is of 4 bytes 
composed of a start byte in which the maximum access number CNT is stored 
and following 3 bytes in which the maximum access frequency track address 
data LBA is stored. 
In the next step S103, of the access frequency counting table (ACS), 
with respect to the file ACSFIL selected at step S3, a record ACSRCD 
corresponding to the point number is selected from the corresponding file 
ACSFIL by using the point number within the 4th index register R4 as an 
index. 
It is determined in decision step S4 whether or not the selected record 
ACSRCD is valid or invalid. This decision is made by determining whether 
or not the numerical value of the first byte of the selected record 
ACSRCD, i.e., the access number data CNT is "0". If the access number data 
CNT is not "0", then the selected record ACSRCD is valid and the 
processing proceeds to the next decision step S105. 
It is determined in decision step S105 whether or not the access number 
stored in the record ACSRCD is larger than the maximum access number CNT 
of the first byte of the maximum value register MAXR. If the access number 
is larger as represented by a YES at decision step S105, then the 
processing proceeds to the next step S106, whereat the track address data 
LBA stored in the selected record ACSRCD is stored in the remaining 3 
bytes of the maximum value register MAXR. Thereafter, the processing 
proceeds to step S107, wherein the access number CNT of the start byte of 
the selected record ACSRCD is overwritten in the region of the first byte 
of the maximum value register MAXR. 
In the next step S108, the point number within the 4th index register R4 is 
updated by addition of "1". In the next decision step S109, it is 
determined whether or not it is carried out to confirm all records ACSRCD 
concerning the selected file ACSFIL have registered data. This decision is 
carried out by determining whether or not the point number stored in the 
4th index register R4 becomes 64. If the point number doe not reach 64 as 
represented by a NO at decision step S109, then the processing returns to 
step S103, wherein the record ACSRCD corresponding to the updated point 
number is selected, whereafter the step S104 and the following steps are 
repeated. 
If the access number CNT registered in the selected record ACSRCD is less 
than the maximum access number of the first byte of the maximum value 
register MAXR as represented by a NO at decision step S105, then the 
processing directly proceeds to step S108, wherein the point number within 
the 4th index register R4 is updated by addition of "1". Then, step S109 
and the following steps are repeated. 
If the point number stored in the 4th index register R4 is greater than 64 
as represented by a YES at decision step S109, then the processing returns 
from this subroutine to the main routine. Then, the processing proceeds to 
the next step S20 shown in FIG. 6. Further, if the first byte of the 
selected record ACSRCD is 0 as represented by a NO at decision step S104, 
then this subroutine is forcibly ended and the processing proceeds to step 
S20 of the main routine. 
As shown in FIG. 6, in step S20, a record MAXRCD corresponding to the 
device No. DNO is selected from the maximum access information table 
(MAX) by using the device No. DNO within the 1st index register R1 as 
an index. 
Then, the processing proceeds to the next step S21, wherein the content of 
the maximum value register MAXR is overwritten on the selected record 
MAXRCD as it is. Specifically, the maximum access number CNT and the 
target track address LBA are stored in the selected record MAXRCD. 
In the next step S22, of the access frequency counting table, the contents 
of the file ACSFIL selected at step S3 are all cleared. For example, "0" 
is stored in the whole region of the file ACSFIL. Then, the processing 
proceeds to step S23, an initial value=0 is stored in the record TTLRCD 
within the count file (TTLCNT) selected at step S16. The processing 
proceeds to the next step S24, whereat a corresponding bit (i.e., bit 
corresponding to the device No. DNO) of the frequency detection flag 
(ACSFLG) is set and then the processing routine of the access frequency 
counting program is ended. 
Of the count file (TTLCNYT), if on the other hand the value of the record 
TTLRCD selected at step S16 is smaller than 64 as represented by a NO at 
decision step S18, then data necessary for detecting the maximum access 
frequency are not yet prepared, and the step S19 and the following steps 
are not executed. Thus, the processing routine of the access frequency 
counting programs is ended directly. 
If the point number is equal to 64 as represented by a YES at decision step 
S8, then it is determined whether or not all records ACSRCD concerning the 
selected file ACSFIL have registered data. Since however the track address 
which is requested to be accessed this time is not registered in the file 
ACSFIL, the processing routine of the access frequency counting program is 
ended directly. 
The access frequency counting program is successively activated after 8 
recording and reproducing apparatus are accessed (accessed to read out) by 
the host computer 32. When the access request is made frequently, 
information concerning the access request (pair of data composed of the 
device No. DNO and the track address data LBA thus access-requested) is 
temporarily stored in the latch region of the FIFO system. Each time the 
access frequency counting program is activated, the information concerning 
the access request is sequentially read out from the latch region and 
processed. 
The processing of the access frequency counting program will be summarized 
below. According to the access frequency counting program, after the 
access request from the host computer 32 is executed by the system 
controller 25, the track address of the access request is registered in 
the access frequency counting table (ACS). Specifically, the access 
number data CNT and the track address data LBA are written in the access 
frequency counting table (ACS). In this write processing, if the track 
address is already written in the table (ACS), then the access number 
data CNT concerning such track address is updated and registered. This 
registration is carried out at the same time when the point number is 
updated. The 64 records are logically allocated to each file so that 64 
kinds of different track addresses can be registered in the table 
(ACS). 
When the point number reaches to 64, the track address having the maximum 
access number and the access number are registered in the maximum access 
information table (MAX). Thus, the track address of maximum frequency 
in the 64 accesses is registered in the maximum access information table 
(MAX). 
At that time, the contents of the access frequency counting table (ACS) 
are cleared by the processing based on the above program, which means that 
the counting starts from the next access again. According to this method, 
it is possible to constantly detect the track address whose access 
frequency is maximum regardless of the cycle and order of the access. In 
addition, since the past 64 points are to be detected, there is then the 
advantage that, even if the track address of high access frequency is 
changed, the access frequency counting program according to the present 
invention can cope with such change readily. 
Access operation done by the system controller 25 when the track address of 
maximum access frequency is detected by the access frequency counting 
program will be described below. 
When the host computer 32 issues an access (read-out) request to the 8 
recording and reproducing apparatus, frequency detection information INF 
is inserted into access request information (ACSINF) shown in FIG. 9 and 
each recording and reproducing apparatus is accessed. As shown in FIG. 9, 
the access request information (ACSINF) is composed of synchronizing 
(sync) information SYC, device No. DNO, the frequency detection 
information INF, track address data LBA, sector address data SBA, and 
read-out record length (sector length) LENGTH, from the start portion in 
that order. 
An example of an insertion processing of the frequency detection 
information INF will be described with reference to a flowchart of FIG. 
10. Following the start of this flowchart, as shown in FIG. 10, it is 
determined in decision step S201 whether or not the track address of high 
access frequency is registered in the access target recording and 
reproducing apparatus. This decision is made by determining whether or not 
the bit corresponding to the access request device No. DNO of the 
frequency detection flag (ACSFLG) shown in FIG. 8D is "1" or "0". 
If the target bit is "1" and the track address of high frequency is 
registered as represented by a YES at decision step S201, then the 
processing proceeds to the next decision step S202. It is determined in 
decision step S202 whether or not the access request track address is the 
same track address registered in the corresponding record MAXRCD of the 
maximum access information table (MAX). If they are the same as 
represented by a YES at decision step S202, then the processing proceeds 
to step S203, whereat the frequency detection information INF is 
registered as "1". If they are not the same as represented by a NO, then 
the processing proceeds to step S204, whereat the frequency detection 
information INF is registered as "0". 
Then, the processing proceeds to step S205, wherein the registered 
frequency detection information INF is inserted into the access request 
information shown in FIG. 9, and the processing is ended. 
If on the other hand the track address of high access frequency is not 
registered in the access request target recording and reproducing 
apparatus as represented by a NO at decision step S201, i.e., the bit 
corresponding to the access request device No. DNO of the frequency 
detection flag (ACSFLG) shown in FIG. 8D is "0", then the processing 
proceeds to step S206, whereat "0" is registered as the frequency 
detection information INF. Thereafter, step S205 and the following steps 
are repeated. 
When the insertion processing of the frequency detection information INF is 
ended, the access request information (ACSINF) thus made is transmitted 
through the interface bus 31 to each recording and reproducing apparatus. 
Processing operation done by each recording and reproducing apparatus will 
be described with reference to a flowchart of FIG. 11. Initially, in step 
S301, each recording and reproducing apparatus temporarily stores the 
access request information (ACSINF) transmitted to the interface bus 31 in 
the RAM provided within the system controller 25. It is determined in 
decision step S302 whether or not its recording and reproducing apparatus 
is a target equipment of this time access request. This decision is made 
by comparing the device No. DNO of the recording and reproducing apparatus 
registered in the ROM provided within the ROM of the system controller 25 
and the device No. DNO within the access request information (ACSINF) 
supplied thereto through the interface bus 31. 
Then, only the recording and reproducing apparatus which is agreed with the 
device NO. DNO within the access request information (ACSINF) becomes the 
access request target equipment. In the next step S303, the system 
controller 25 of the corresponding apparatus reeds out data conforming to 
the request information from the optical disc in accordance with the 
access request information (ACSINF) latched in the RAM. In this data 
read-out processing, in order to detect the present position of the 
optical head on the track, data on the optical disc 1 is temporarily read 
out by the optical head 4, Then, data concerning the address is extracted 
from the data thus read out and supplied to the system controller 25. The 
system controller 25 calculates the moving amount of the optical head 4 by 
comparing the address thus read out and the access request address. 
Thereafter, the moving amount data thus calculated is supplied to the servo 
controller 24 and the optical head 4 is placed at the access request track 
under the control of the servo controller 24. Simultaneously, the optical 
head 4 reads out the data on that track based on the access request 
information (sector address and record length). The data thus read out by 
the optical head 4 is converted by the demodulator 22 to predetermined 
reproduced data which is supplied through the interface bus 31 to the host 
computer 32. 
In the next step S304, time data indicative of 3 seconds is set to the 
counter (not shown) provided within the system controller 25. 
It is determined in the next decision step S305 by the system controller 25 
on the basis of the frequency detection information INF provided within 
the access request information (ACSINF) latched in the RAM whether or not 
the accessed track is the track of maximum access frequency. This decision 
is made by detecting whether the content of the frequency detection 
information INF is "1" or "0". 
If the accessed track is the track of maximum access frequency as 
represented by a YES at decision step S305, i.e., the content of the 
frequency detection information INF is "1", then the processing proceeds 
to step S306, wherein a random number is generated. The random number 
falls within a range of track number within a visual field of the 
objective lens 12 in the optical head 4, i.e., an operation range (region 
d shown hatched in FIG. 2) of the objective lens 12 by the tracking coil 
and the magnet of the two-dimensional actuator 13. In this embodiment, the 
track is .+-.50 track and a random number of arbitrary numerical value in 
the range of .+-.50 may be generated. If on the other hand the accessed 
track is not the track of maximum access frequency as represented by a NO 
at decision step S305, then the processing proceeds to step S308. 
In step S307, the system controller 25 outputs the servo signal to the 
servo controller 24 to drive the two-dimensional actuator 13 such that the 
focusing of the objective lens 12 coincides the track of the numerical 
value indicated by the random number thus generated. When the 
two-dimensional actuator 13 is energized by the servo controller 24, the 
objective lens 12 is moved by a very small amount to the track array 
direction at the time unit of 1 msec/per track until the focusing of the 
objective lens 12 coincides with the track. 
It is determined in the next decision step S308 whether or not the access 
request is made. If the access request is made as represented by a YES at 
decision step S308, then the processing is ended as it is and the 
processing corresponding to the next access request is executed. If on the 
other hand the access request is not made as represented by a NO at 
decision step S308, then the processing proceeds to the next decision step 
S309. It is determined in decision step S309 whether or not the time set 
by the step S304 is elapsed. If the predetermined time is not elapsed as 
represented by a NO at decision step S309, then the processing returns to 
step S306, whereat a random number is generated again. If the 
predetermined time is elapsed as represented by a YES at decision step 
S309, i.e., 3 seconds are elapsed after the previous access was made, then 
the processing proceeds to step S310, whereat the optical head 4 is moved 
to the home position a (see FIG. 2). Then, the processing is ended. 
While an interrupt accompanying with the elapse of 3 seconds from the 
counter also is determined at step S309 as described above, the present 
invention is not limited thereto and the interrupt accompanying with the 
next access request, i.e., only step S308 may be determined as an 
interrupt target. In this case, the steps S309 and S310 may be omitted and 
the processing may directly be returned to step S306 if a NO is output at 
decision step S308. 
As described above, according to the recording and reproducing apparatus of 
the present invention, when the access request is made on the track of 
high access frequency, after the access on the corresponding track is 
finished, the optical head 4 is not stopped on the track for a 
predetermined time but moved very slightly to the arbitrary track within 
the range d of .+-.50 tracks. Thus, until the interrupt accompanying with 
the elapse of 3 seconds from the counter or the interrupt accompanying 
with the next access request occurs, the optical head 4 is swingably moved 
around the track of the maximum access frequency. 
Accordingly, it is possible to prevent in advance the optical disc 1 from 
being heated when the optical disc 1 is radiated at the same position by 
the laser beam L emitted from the optical head 4 for a long period of 
time. Specifically, the laser beam L emitted from the optical head 4 
radiates around the track of the maximum access frequency so that 
radiation of the laser beam L can be avoided from being concentrated on 
the same track. In addition, since the movement of the optical head from 
the center of the track of the maximum access frequency to the surrounding 
tracks is determined by the random number, the laser beam L can be 
equivalently distributed to the surrounding tracks. Thus, it is possible 
to disperse the occurrence of heat generated by the laser beam L over the 
surrounding tracks. Also, it is possible to prevent heat from being 
accumulated on the optical disc when the laser beam L radiates the same 
track of the optical disc for a long period of time. 
Further, since the optical head 4 is swingably moved around the track of 
the maximum access frequency, as compared with the case that the optical 
head 4 is frequently returned to the home position a, the movement of the 
optical head 4 in the next access and the access to the track of the 
maximum access frequency can be made at higher speed. Thus, the access 
speed of the optical head 4 can be increased. 
A further embodiment of the present invention will be described below with 
reference to a flowchart of FIG. 12. In this embodiment, processings from 
steps S401 to S407 are similar to those of the embodiment shown in FIG. 11 
and therefore need not be described. According to this embodiment, it is 
determined in decision step S408 whether or not the access request is 
made. If the access request is made as represented by a YES at decision 
step S408, then the processing is ended and the processing corresponding 
to the next access request is executed. If on the other hand the access 
request is not made as represented by a NO at decision step S408, then the 
processing proceeds to the next decision step S409. It is determined in 
decision step S409 whether or not the time set at step S404 is set. If the 
predetermined time is not elapsed as represented by a NO at decision step 
S409, then the processing returns to step S408. If the predetermined time 
is elapsed as represented by a YES at decision step S409, then the 
processing proceeds to step S410, whereat the optical head 4 is moved to 
the home position a and the processing is ended. 
In the case of this embodiment, although only the track other than the 
maximum access track is accessed for 3 seconds, no such large influence is 
exerted upon that track. It is rather important that the maximum access 
track can be accessed in a short period of time when the maximum access 
track is accessed again within 3 seconds. Even when the maximum track is 
accessed continuously at the interval of less than 3 seconds, the optical 
head 4 is moved near the track. Thus, unlike the prior art, the optical 
head can be prevented from continuously accessing only the maximum access 
track. 
While the system controllers 25 execute the processings in the flowchart 
shown in FIGS. 11 and 12 as described above, the present invention is not 
limited thereto and the interface command controller 43 may execute such 
processings. In this case, the processings in the steps S302 and S402 may 
be replaced with processings in which a target equipment is selected. 
While the time data indicative of 3 seconds is used as the data set to the 
counter as described above, the present invention is not limited thereto 
and the following variant also is possible. Because there is then no risk 
that heat is accumulated on the optical disc, the value of the time data 
can be increased and arbitrary values, such as 4 seconds and 6 seconds can 
be freely used as the time data. Thus, it is possible to make the access 
speed of the optical head 4 high. 
While the phase-change type optical disc 1 is used as the recording medium 
as described above, the present invention is not limited thereto and a 
magneto-optical disc may be used as other recording media. Also in this 
case, it is possible to prevent in advance the film from being changed by 
heat accumulated in the magneto-optical disc. 
While there is provided only one maximum access track, the present 
invention is not limited thereto and a plurality of maximum access tracks 
may of course be provided. In this case, since the maximum access track is 
updated and two tracks or more will not be the maximum access tracks for a 
long period of time. There is then the small possibility that a serious 
trouble will occur. 
As described above, since the recording and reproducing apparatus according 
to the present invention comprises the access head for accessing an 
information signal from the recording medium, the detecting means for 
counting frequency with which the access head accesses the same recording 
unit region of the recording medium and detecting the recording unit 
region of high access frequency and the swinging means for swinging the 
access head on the recording medium until the next access request when the 
access head accesses the recording unit region of the high access 
frequency detected by the detecting means, it is possible to prevent the 
access head from staying at the same position for a long period of time. 
In addition, it is possible to achieve high access speed. 
When the above-mentioned recording and reproducing apparatus comprises the 
moving means for moving the access head to the outside of the region in 
which the recording unit regions are collected on the basis of the 
detected result representing that the access head is stopped at least on 
the arbitrary recording unit region for a predetermined period of time, it 
becomes possible to reduce a power consumption and to extend mechanical 
lifetime of the servo system. 
Further, when the swinging means is energized to swingably move the access 
head within the pseudo-region allocated about the recording unit region of 
the high access frequency detected by the detecting means, it is possible 
to simplify the arrangement of the recording and reproducing apparatus 
itself. 
Furthermore, when the recording medium is formed of the phase-change type 
optical disc, the access head is formed of the optical head, the swinging 
means is formed of the actuator for swingably moving the objective lens of 
the optical head along the direction in which the tracks of the 
phase-change type optical disc are arrayed, the moving means is formed of 
the mechanism for moving the optical head in the diameter direction of the 
phase-change type optical disc and the recording unit region of the high 
access frequency detected by the detecting means is formed of the track of 
the phase-change type optical disc, it is possible to prevent in advance 
from heat being accumulated in the phase-change type optical disc when 
laser beam emitted from the optical head radiates the same position of the 
optical disc for a long period of time. In addition, the optical head can 
be moved at high speed to access the optical disc next and can access the 
track of high access frequency at high speed. Thus, the access speed of 
the optical head can be increased. 
Having described preferred embodiments of the invention with reference to 
the accompanying drawings, it is to be understood that the invention is 
not limited to those precise embodiments and that various changes and 
modifications could be effected therein by one skilled in the art without 
departing from the spirit or scope of the invention as defined in the 
appended claims.