High speed information retrieval apparatus

A high speed information retrieval apparatus that carries out program retrieval and reproduction on the basis of program numbers used as subcodes corresponding to individual information programs recorded on the magnetic tape. Two high speed search operations are used in moving the tape from a current position to an object position. A memory is used to store code representations of program positions, and a position information calculation circuit determines tape position based on a detection of tape reel rotation. In one high speed search mode, the memory and calculation circuit output are compared to determine position. In another high speed search mode, the subcode on the tape is compared to a current tape position. When the object program number is stored in the memory, the mechanism block is set to a second high speed running mode by a control circuit. The block stays in that mode until the current tape position comes within a threshold distance of the object position. When the object position is not stored in the memory, or the threshold distance is reached in the second mode, the mechanism block is set to a first high speed running mode.

FIELD OF THE INVENTION 
The present invention relates to a high speed information retrieval 
apparatus which retrieves and reproduces desired information programs at a 
high speed based on the use of program numbers. The numbers comprise 
subcode information that corresponds to individual information programs 
recorded on a magnetic tape in an R-DAT (rotary head type digital audio 
tape recorder) or 8 mm video tape recorder. 
BACKGROUND OF THE INVENTION 
One example of an apparatus that can realize the retrieval of desired 
information programs based on the program number (PNO) is illustrated in 
FIG. 6. In this figure, a mechanism block 1 contains a magnetic tape 2 
having program numbers corresponding to a plurality of information 
programs. The magnetic tape is wound on supply reel 7 and take-up reel 8. 
The tape runs along the circumferential surface of a rotary drum 3, within 
a section having an angular range of 90.degree.. The tape loads a pair of 
heads 4a, 4b arranged with an angular interval of 180.degree.. capstan 5 
and pinch roller 6 operate to drive the magnetic tape 2 in a conventional 
manner. For example, when the magnetic tape 2 is run at an ordinary speed 
for reproduction or even at an intermediate speed (about 10 times or more 
than the ordinary speed). the driving force of he capstan 5 and pinch 
roller 6 is adequate. However, when the tape is run at a high speed (about 
100 times to 200 times the ordinary speed for reproduction) it is driven 
by the supply reel 7 or take-up reel 8. 
A reproduction amplifier 9 is connected to the block 1 and amplifies 
reproduced signals alternately picked up from the heads 4a, 4b. A program 
number reproducing circuit 10 receives the amplified signals and operates 
to reproduce program numbers, as subcode information, from the heads 4a, 
4b sent via reproduction amplifier 9. A current program number holding 
circuit 11 holds program numbers of the current position reproduced by the 
program number reproducing circuit 10. 
An operation part 12 sends to a control circuit 15 and an object PNO 
holding circuit 13 a program number input identifying a desired search 
position. Control circuit 15 produces an initiation instruction input for 
controlling the reproducing operation of the information program and the 
search operation. Object program number holding circuit 13 operates to 
hold program numbers identified as a search position input by the 
operation part 12. Program number comparison circuit 14 acts to compare 
values of the program numbers held in the current program number holding 
circuit 11 and object program number holding circuit 13. Control circuit 
15 controls a mechanism drive circuit 16 based on an output sent from the 
operation part 12 and program number comparison circuit 14. Circuit 15 
also controls the mechanism block 1 in an operation mode, such as a 
reproduction mode, and in a search mode, such as a search operation for 
information programs. 
The operation of an apparatus having the structure of FIG. 6 may be easily 
explained. Let it be assumed that a program number of the desired search 
position is designated by the operation part 12. A program number 
reproduced by the program number reproducing circuit 10 is held in the 
current program number holding circuit 11. Let it also be assumed that the 
program number of the search position is held in the object program number 
holding circuit 13. 
When initiation of a search operation is designated by the operation part 
12, the control circuit 15 Will shift the mechanism drive circuit 16 to 
the high speed search operation mode in the FWD or REV direction based on 
the output from the program number comparison circuit 14, namely the 
result of a comparison of values of the current program number and object 
program number. In this manner, the mechanism drive circuit 16 
controllably drives the mechanism block 1. 
During the high speed search operation, the control circuit 15 always 
Watches the output of the program number comparison circuit 14. When the 
program numbers in the current program number holding circuit 11 and the 
object program number holding circuit 13 match, the control circuit 15 
controls the mechanism drive circuit 16 to set the mechanism block 1 to an 
intermediate speed running condition. In this manner the apparatus 
initiates a so-called "precise quick-start of reproduction". 
When the object program number is detected during preparation for a precise 
quick-start of reproduction, the search operation at the desired search 
position is completed. However, if the starting end or terminating end of 
the magnetic tape is detected by a detection means (not illustrated) 
during the high speed search operation, the high speed search operation is 
interrupted. 
In one approach, while the magnetic tape 2 is caused to run at a high speed 
in a high speed search operation, the program numbers recorded on the 
magnetic tape 2 are reproduced by the program number reproducing circuit 
10 and, simultaneously, the search position in which the object program 
number is recorded is retrieved. However, in the case of the R-DAT format 
identified above, the program numbers are recorded only in the 300 frames 
(9 seconds at the speed of ordinary reproducing operation) at the heading 
section of individual information programs. Therefore when the magnetic 
tape is caused to run at 200 times the speed of the ordinary reproducing 
operation, for example, during the high speed search operation, the head 
passes the part recording the program numbers only during a period of 45 
msec. 
To solve this problem for the R-DAT format, a so-called relative speed 
servo technique is employed for realizing the high speed search operation. 
In particular, the number of rotations of rotary drum 3 is changed in 
accordance with the running speed of magnetic tape 2. Thus, the relative 
speed of recorded patterns with respect to the head during the high speed 
search operation in the R-DAT is fixed. Specifically, during the high 
speed search operation, the drum rotates at about 200 times its speed in 
the ordinary reproducing operation. The high rotational speed is used 
primarily in the REV direction. However, the signal reproduced from the 
magnetic tape includes a variety of distortions and does not appear in an 
ideal condition. Therefore, the magnetic tape running speed in the actual 
high speed search operation has been set to a speed slightly lower than 
200 times that of the ordinary reproduction speed. The lower speed is 
designed to provide a margin for always realizing a stable high speed 
search operation. 
As explained previously it is necessary in the above-described approach to 
always read the program numbers recorded on the magnetic tape during the 
high speed search operation. It also is necessary for the running speed of 
magnetic tape to be set to a speed significantly lower than the upper 
limit defined by mechanism limitations (for instance, the speed at which 
the magnetic tape runs stably and is not subject to damage). This speed 
occurs, for example, at only 150 times the ordinary reproducing speed in 
order to always read, under a stabilized condition, the subcode 
information such as program numbers on the magnetic tape. 
Because of these competing considerations, the high speed retrieval 
technique used in the current R-DAT system may not provide sufficient high 
speed retrieval performance. Moreover, it also has been difficult to 
exceed the upper limit of the retrieval speed, due to the format used in 
R-DAT. 
SUMMARY OF THE INVENTION 
The present invention has been proposed to eliminate problems of the 
above-described approach. Therefore, it is an object of the present 
invention to provide an information high speed retrieval apparatus which 
realizes high speed retrieval of desired information programs based on 
program numbers recorded on a magnetic tape corresponding to individual 
recorded information programs. 
The high speed information retrieval apparatus of the present invention 
comprises a rotation detector which detects the rotation of both the 
supply reel and the take-up reel or either one of them. It also comprises 
a position information calculation circuit which performs a calculation 
based on the rotation information from the rotation detector and, thereby, 
obtains the current position on the magnetic tape. It further comprises a 
program number reproducing circuit which controls the magnetic tape and 
head speed at a level equal to the speed in the ordinary reproducing 
operation. 
For example, when the magnetic tape runs at a speed 200 
times the speed of the ordinary reproducing operation, the relative speed 
of the recording patterns with respect to the head according to the 
relative speed servo technique can be made constant by setting a number of 
rotations of the rotary drum to about 3000 rpm in the FWD direction and 
about 1000 rpm in the REV direction. When a high speed search operation is 
required, i.e., an operation at 200 times the speed of an ordinary 
reproducing operation in the REV direction, the rotation frequency of 
rotary drum becomes about 60 msec, based on the number of rotations of the 
rotary drum. 
When such running speeds are used for magnetic tape, the head passes the 
tape portion recording program numbers in only 45 msec. Therefore, during 
the high speed search operation at 200 times or more the speed of an 
ordinary reproducing operation, the tape portion that contains the program 
numbers passes the head during a single rotation of the rotary drum. As a 
result, the readout frequency of the program number can be lowered 
significantly. 
In general, multiplex matching of readout data is checked in order to 
provide reliability to the readout of a subcode during the high speed 
search operation. Also, at the upper limit of the running speed of the 
magnetic tape, program numbers recorded on the magnetic tape may be 
reproduced by using a memory which stores program numbers obtained by 
reproduction through the program number reproducing circuit and 
corresponding position information sent from the position information 
calculation circuit. Using this system the mechanism block is placed into 
a first high speed running mode when the object program number position is 
not stored in the memory during the high speed retrieval operation and the 
mechanism block is placed into a second high speed running mode in which 
the tape runs at a higher speed than the first high speed running mode 
when the object program number position is stored in the above memory, 
thereby significantly improving the retrieval speed in the high speed 
information retrieval operation.

DETAILED DESCRIPTION OF THE INVENTION 
An embodiment of the present invention is explained hereunder with 
reference to the accompanying drawings. 
FIG. 1 is a block diagram of a preferred embodiment of a high speed 
information retrieval apparatus of the present invention. The embodiment 
is for high speed information retrieval in R-DAT. The elements similar to 
those in FIG. 6 are given an identical reference number and a detailed 
explanation of these elements is omitted. 
In FIG. 1, a rotation detector 17 detects the rotation of the supply reel 7 
and a rotation detector 18 detects rotation of the take-up reel 8. A 
position information calculation circuit 19 carries out a calculation 
based on rotation information which is output from the rotation detectors 
17 and 18 and obtains a current position of the magnetic tape 2. A memory 
20, which receives an output from the position information calculation 
circuit 19. stores, position information concerning the magnetic tape 2, 
and a corresponding program number for every reproduction of a program 
number generated by the program number reproducing circuit 10. 
FIG. 3 illustrates the storage in the memory 20 of the program numbers, 
obtained by reproduction through the program number reproducing circuit 
10, and corresponding position information on the magnetic tape 2 obtained 
as an output of the position information calculation circuit 19. Memory 20 
stores the program numbers (1-11) recorded at the heading part of 
individual information programs. The numbers increase in value from the 
starting end of the magnetic tape 2 to the end thereof. Also stored is the 
corresponding position information on the magnetic tape 2 (e.g., 
0010-1200). The position information "EEEE", corresponding to the program 
number "12"in FIG. 3, indicates that the position of such program number 
on the magnetic tape is still unknown. .In this example, the position of 
program number "12"is unknown. 
The operation of an apparatus having such structure may be explained with 
reference to the flowcharts of FIG. 2A and FIG. 2B. 
When an instruction for operations such as PLAY, FF, REW, CUE, REVIEW is 
issued from the operation part 12, the control circuit 15 controls the 
mechanism drive circuit 16. In this operation mode, circuit 16 drives and 
controls the mechanism block 1 in the designated operation mode. 
For each detection and reproduction of program number information from the 
magnetic tape 2 by the program number reproducing circuit 10 under the 
operating condition such as PLAY, FF, REW, CUE and REVIEW. the memory 20 
stores outputs of the position information calculation circuit 19. 
Specifically, the position information on the magnetic tape 2 where the 
program number information is recorded, corresponding to program numbers 
obtained by the reproduction as explained above, is stored. 
In operation of the invention, program numbers will be reproduced from the 
magnetic tape 2 by the program number reproducing circuit 10. Also, a 
search operation for a program number will be designated by the operation 
part 12. Such program number will be held in the current program number 
holding circuit 11. 
In a first case, the position of an object program number recorded on the 
magnetic tape may not be known. Specifically, the position information 
corresponding to the object program number is not stored in the memory 20. 
In this case, operations similar to these explained with regard to the 
disadvantageous approach are conducted. The magnetic tape during the high 
speed search operation is operated in a first high speed running mode. 
However, as previously explained, the actual speed is reduced in order to 
permit stable reading of the subcode information, such as the program 
number. For each detection and reproduction of a program number, as a 
search is being conducted for an object program number, the memory 20 
stores outputs of the position information calculation circuit 19 
corresponding to the reproduced program number. 
Referring to the flowchart of FIG. 2A, when the search operation start 
instruction is input to the step S1 from the operation part 12, it is 
decided in the step S2 by the control circuit 15 whether or not the object 
program number position is stored in the memory 20. When it is decided 
that the position information for the object program is not stored, the 
current program number is compared with the object program number by the 
program number comparison circuit 14 in the step S3. 
When the current program number is equal to the object program number, the 
precise quick-start operation is carried out in the step S4. In case the 
current program number is larger than the object program number, in step 
S5. a running (first high speed running mode) in the REV direction is 
started. This first high speed is only 150 times the operational speed. 
During this search operation, it is decided in the step S6 whether or not 
the current program number is equal to the object program number. When 
both program numbers are equal, the operation moves to the step S4 and a 
precise quick-start operation is carried out. When the two program numbers 
are not equal, a determination is made in the step S7 of whether or not 
the tape is at an end. When the tape is found to be at an end, the search 
operation is suspended in the step S8, resulting in the stop condition. 
When the tape is not at an end, the process returns to step S6 where a 
comparison of the two program numbers is again conducted. 
When it is decided in the step S3 that the current program number is 
smaller than the object program number, step 9 begins and the tape is run 
at a speed of 150 times the operational speed in the FWD direction (first 
high speed running mode). Once this step begins, it is also decided in 
step S10 whether or not the current program number is equal to the object 
program number during the search operation. When both program numbers 
become equal, the operation moves to step S4 and the precise quick-start 
operation is carried out. If both program numbers are not equal, it is 
decided in the step S11 whether or not the tape end has been detected. 
When the tape end is detected, the search operation is suspended, 
resulting in the stop condition in the step S8. When the tape end is not 
detected, the process returns to step S10 where a comparison of the two 
program numbers is again conducted. 
In the second case, the position on the magnetic tape recording the object 
program number is known. In this case, the control circuit 15 compares an 
output of the position information calculation circuit 19, namely the 
current position on the magnetic tape, with the magnetic tape position of 
object program number stored in the memory 20. When it is decided that the 
difference is smaller than a threshold value, namely the object program 
number is sufficiently close to the current position, the search operation 
is carried out at the speed of 150 times the operational speed in a manner 
explained previously. 
However, when the distance between the current position and the object 
program number position is larger than threshold value, the control 
circuit 15 controls the mechanism drive circuit 16 based on the result of 
the comparison between the current position information as an output of 
the position information calculation circuit 19, and the object program 
number position information stored in the memory 20. The drive circuit 16 
will set the mechanism block 1 to the high speed running mode in the FWD 
or REV direction, as appropriate. 
In this case, the running mode need not always be set to a high speed mode 
in which the subcode information, such as program number, may accurately 
be read out. Therefore, the running is in the second high speed running 
mode, which is higher than the first high speed running mode, as explained 
previously. In this second high speed running mode, the control circuit 15 
always compares an output of the position information calculation circuit 
19 and the object program number position information stored in the memory 
20. When the difference between them is smaller than a threshold value 
that is, the object program number position is sufficiently close to the 
current position, the control circuit 15 controls the mechanism drive 
circuit 16 to set the mechanism block 1 to the first high speed running 
mode as explained above. Thereafter, the search operation is carried in 
the same way as that explained for the case where the position of object 
program number recorded on the magnetic tape is unknown. 
Referring to the flowcharts of FIGS. 2A and 2B, when it is decided in the 
step S2 that the object program number position is known, the operation 
moves to the step S12. There the difference between the current position 
and object program number position is determined. The symbol d in FIG. 2B 
indicates a threshold value and it is used as an index for deciding 
whether or not the object program number position is sufficiently close to 
the current position. In case it is decided in the step S12 that 
difference is smaller than or equal to d, the operation moves to the step 
S3 and the first high speed operations, as previously explained, are 
carried out. 
When difference is larger than the threshold value d, the values of the 
current position and the object program number position are compared in 
step S13. When the current position is larger than the object program 
number position, in the step S14 running in the speed of 300 times (second 
high speed running mode) in the REV direction is started. In the step S15, 
the current position is compared again with the object program number 
position. When it is decided that the difference becomes equal to or 
smaller than the present value d, the speed is changed to 150 times the 
operation speed in the step S16. Thereafter, the operations explained 
above are carried out beginning at step S6. 
If in the step S13 it is decided that the current position is smaller than 
the object program number positions, the process moves to step S17 and 
running (second high speed running mode) is started in the speed of 300 
times the operational speed in the FWD direction. In the step S18, the 
current position is compared with the object program number position. When 
difference is equal to or smaller than the threshold value d, the speed is 
changed to 150 times in the step S19 and thereafter operations are carried 
out in the step S10. 
FIG. 4 shows the running condition of a magnetic tape during the high speed 
information retrieval explained above. In this example, the object program 
number is set to "11". A solid line shows the case where the position 
information of the object program number is known. At the beginning of the 
object program number position search (right-most portion of the plotted 
.running condition graph), the magnetic tape is caused to run in the speed 
of 300 times the operational speed (second high speed running mode). The 
tape speed is then changed based on the preset value d, to 150 times the 
operational speed (first high speed running mode) at a time when the 
object program number position is found to be sufficiently close to the 
current position. 
A dashed line shows the case where the object program number position 
information is unknown and the magnetic tape is caused to run at the speed 
of 150 times the operational speed (first high speed running mode) for the 
entire section. Moreover, the dashed line also indicates the running 
condition of magnetic tape in above-described disadvantageous approach. 
In the embodiment explained previously, when the position information of 
object program number is unknown, the tape is run in the first high speed 
running mode, which is rather lower than the second high speed running 
mode, in order to read the subcode information, such as program number, 
under the condition that the magnetic tape is always stabilized. 
The operation of the present invention can further maximize operational 
efficiency by making fully use of the position information of program 
numbers which are already known. As an example, if the position 
information of the object program number is not known while the position 
information of a program number in the vicinity of object program number 
is known, the tape is run at the second high speed running mode, wherein 
the subcode information such as program number is not always read until 
close to the vicinity of the known program number position, and thereafter 
the tape is run in the first high speed running mode. Thereby, a more 
useful result can be obtained. 
FIG. 5 shows the magnetic tape running condition in such a case. The 
position information having an object program number "11" is unknown and 
the position information having a program number "10" is known. 
In the embodiment explained above, the rotation information of both supply 
and take-up reels is used as the input to the position information 
calculation circuit. However, in case such accuracy as detecting rotations 
of both reels and making calculation is not required, rotation of any one 
reel is detected and calculation is carried out in order to obtain the 
position information and thereby realize low cost. 
In addition in the embodiment explained previously, writing position 
information of program number to the memory is gradually carried out when 
a user makes operations of PLAY, FF and REW. etc. However, it is also 
possible to automatically carry out the FF or REW operation at the time of 
loading the magnetic tape and writing is carried out at a different time. 
According to the present invention explained earlier, when the position 
information of object program number is unknown, the magnetic tape is 
controlled to the first high speed running mode and when the position 
information of object program number is known, the magnetic tape is 
controlled to the second high speed running mode which is higher than the 
first running mode. Thereby, information retrieval operation speed can be 
improved significantly.