Memory guided magnetic tape tracking

A self-aligning configuration for establishing precisely where each of any number of tracks is to be recorded on a magnetic tape, utilizes therefor a photosensitive element (of perhaps even coarser structure than that of a given track), the signal output of which constitutes a measure of the location of the track(s). Thereafter, tracking control, say during playback, is pursuant to such signal, which is memorized.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates in general to magnetic recording and more 
particularly to improved apparatus for providing tracking control during 
the playback of recorded signal information. 
2. Description Relative to the Prior Art 
There is a trend toward the packing of greater and greater amounts of data 
on magnetic tape. Implicit in such trend is the requirement that data 
tracks on such tape be as narrow, and as closely spaced together, as 
possible. It is clearly of concern, therefore, that during playback of 
recorded information, that the information so recovered be from the 
correct track, and not from a neighboring one. 
It is known in the art to record tracking control signals on a magnetic 
tape as a vehicle for preventing head-to-tape wander during playback of 
information recorded on the tape. Representative prior art in this 
connection may be found in U.S. Pat. No. 3,474,432, which depicts the use 
of various prerecorded frequencies in respective tracks, the signals being 
mixed in such a way as to cause head position error signals to be 
generated in response to head-to-tape wander. Similarly, more recently 
issued U.S. Pat. No. 4,258,398 calls for the use of paired pre-recorded 
tracks as signal-sources for head orienting/positioning in connection with 
a multitrack configuration. Other and varied tracking control techniques 
have been demonstrated and taught in the art, albeit that such techniques 
exhibit less than optimally tight-control and, accordingly, are wanting 
when it comes to the matter of sensitivity. 
SUMMARY OF THE INVENTION 
The present invention provides a self-aligning configuration for 
establishing precisely where each of any number of tracks is to be 
recorded on a magnetic tape, and utilizes therefor a photosensitive 
element (of perhaps even coarser structure than that of a given track), 
the signal output of which constitutes a measure of the location of the 
track(s). Thereafter, tracking control, say during playback, is pursuant 
to such signal, which is memorized. In a presently preferred embodiment of 
the invention, the photosensitive element is a charge-coupled device 
(CCD). A set-up tape having a pre-recorded track (or tracks) thereon is 
read, with signals corresponding to the head position for such 
pre-recorded track, or tracks, being stored in respective PROMs. Given 
that such PROMs are set-up with "true" track location information, 
recording and playback thereafter is under control of output signals from 
the PROMs.

DETAILED DESCRIPTION 
Referring to FIGS. 1 and 2, a multitrack Read/Write head 10 is depicted as 
having, by way of example, three Write cores 12, and three corresponding 
Read cores 14. Note that the Read cores 14 have narrower geometries than 
their corresponding Write cores 12. The spacing between Write cores 12, in 
this embodiment of the invention, is such that the core pitch is n (number 
of Write cores) times the track width (TW), thereby effecting what would 
be contiguous tracks on recording tape 16. Because they have narrower 
geometries than their corresponding Write cores 12, the Read cores are 
ensconced "within" recorded tracks 18, rather than overlapping such 
tracks. This means that the Read cores during playback do not pick up 
unwanted signals from adjacent tracks. 
A laser 20, utilizing feedback 22 for purposes of uniform output, 
illuminates, via optics 23, the edge 24 of the tape 16, and part of a 
photosensor 26, which partially falls in the shadow of the edge of the 
tape. The output of the photosensor 26 is applied to a control circuit 28 
for controlling the relative trackwise positioning between the head 10 and 
tape 16. 
Operation is as follows: with the tape 16 threaded up, the tape edge 24 
shadows the photosensor 26 so as to cause its signal output to be at a 
certain level. Such signal level is quantized (analog-to-digital converter 
30), and then applied to both a counter 32 (via a set-up gate 33) and a 
comparator 34. The counter 32 effectively memorizes the widthwise start 
location of the tape, and thereafter (as the tape 16 is run) has its 
output continuously compared to the instantaneous widthwise location of 
the tape. As a result of such comparison, an actuator 36 (solenoid or 
equivalent) continuously keeps the head 10 (Write cores 1, 2, 3 on their 
"self-aligned" tracks. 
At the end (EOT) of the first set of three tracks being recorded, a "count 
change" is applied to the counter 32, thereby causing the comparator 34 to 
produce a head-position correction signal for application to the actuator 
36. Attendantly, the head indexes over so that a second set of three 
tracks may be recorded, this time under control of the up-dated counter 32 
output. The second set of three tracks is contiguous with respective 
tracks of the first set of three tracks, and in perfect alignment 
therewith as a result of the comparison between the up-dated count of the 
counter 32 and the instantaneous output of the A/D converter 30. Again, at 
the end of the second set of three tracks (EOT), a new count-change is 
effected, whereby a third set of three tracks is recorded in like manner. 
At the end of the third set of three tracks, an end-of-recording signal 
(EOR) is generated, causing the counter 32 and the actuator 36 to reset to 
their respective start conditions, in readiness for playback, or a new 
recording. 
As aforesaid, the invention in its presently preferred form utilizes a CCD, 
cooperative with PROMs, for set-up and control of tracking: With reference 
to the schematic showing of FIG. 3, consider the edge 24' of set-up tape 
16' as shadowing a linear CCD 26', as indicated. (Character designations 
in FIG. 3, which correspond to related parts appearing in FIG. 1, are 
indicated by the use of primes.) Given that the set-up tape is run while 
tracking a first pre-recorded track of the set-up tape, the CCD is clocked 
to produce periodic samples (sample and hold circuit 40) of the location 
of the edge 24' of the set-up tape. Such samples are quantized 
(analog-to-digital converter 42), and applied, in cooperation with a PROM 
selecting matrix 45 (under addressing control of a counter 44), to a first 
PROM T-1. (Note that the edge 24' of the tape 16' falls within a cell c of 
the CCD 26'. While the cells a, b of the CCD 26' produce analog signals of 
one level, and the cells n, n-1, n-2 produce analog signals of a different 
level, the CCD cell c produces an analog signal level precisely indicative 
of the location of the tape edge 24' therewithin, and can be used for 
precise tracking control, irrespective of tight trackwidth dimensions.) 
Thus, during the first running traversal of the tape 16', the PROM T-1 is 
loaded with tracking control information corresponding to the location of 
a first track that is widthwise of the tape 16'. 
At a pre-selected count of the counter 44, which count corresponds to an 
end-of-tape (EOT) situation, the counter is reset, and the head indexed to 
a new location corresponding to a second track of the set-up tape. 
Attendantly, the edge 24' of the tape 16' shadows a new cell of the CCD 
26'. As the tape is run again, the CCD is again clocked to produce a new 
set of tracking control signal information that is loaded into a second 
PROM T-2, cooperative with the PROM-selecting matrix 45, and under 
addressing control of the counter 44. 
The above procedure is repeated for each track location of the set-up tape, 
so that eventually each PROM T-1 through T-N is loaded with tracking 
control signal information respective of the recorded set-up tracks. With 
the PROMs so set-up, the set-up tape is then removed . . . and two set-up 
switches thrown. Now, when a tape to be recorded is run, the clocked 
output of the CCD 26' is continually compared (comparator 34') with 
memorized tracking information stored in the PROM that is respective of 
the track being recorded. Attendantly, tracking control for both recording 
and playback is as tight as was employed with the set-up tape. 
The invention has been described in detail with particular reference to a 
presently preferred embodiment, but it will be understood that variations 
and modifications can be effected within the spirit and scope of the 
invention. For example, while various compensating delay devices are not 
indicated in connection with either FIGS. 1 or 3, it is obvious that such 
may be provided as required.