Method and apparatus for video signal recording

A method and apparatus for video signal recording comprises helically scanning a plurality of transducer heads sequentially along separate parallel paths of equal width on a record medium at a rate such that a plurality of the scans occur within a field interval, and diverting the signal in predetermined sequence to different ones of the heads. The scanning of said heads and diverting of the signal to different heads is arranged to cause some redundant recording of information in different ones of the paths, information recorded in a path that is adjacent an edge of the medium having corresponding redundant information recorded in an internal path that is bounded by other parallel paths. The apparatus includes a rotary scanner having at least three transducer heads spaced along and around the axis of rotation of the scanner whereby each head scans along a different circular orbit and at a different time across a segment of a cylindrical surface defined by the plural orbits, and a transport for moving a recording tape across a segment of such cylindrical surface in timed relation to scanning rotation of the heads and at an angle to the axis of rotation such that each head traces a series of helical scans on the medium within non-overlapping paths along the direction of motion of the medium. The heads rotate at a speed sufficient to separate each scan of a head along the corresponding path.

BACKGROUND OF THE INVENTION 
This invention relates to a wide band magnetic recording system and 
particularly to types of scanners and scanning formats for magnetic 
recorders in which the transducer heads are continuously scanned at a 
relatively higher velocity past a moving record media, such as recording 
tape, which is moving at a substantially lesser velocity. 
A number of different types of scanners have been known. One of the first 
in wide commercial use was the socalled transverse scan, quad format, 
which is typified by the many presently used studio television recorders. 
It is disclosed in U.S. Pat. Nos. 2,912,518, and 2,956,114. A relatively 
wide tape is moved along its length, and at the recording station the 
cross section of the tape is formed to take the shape of a section of a 
cylinder. The arc of the section may be slightly in excess of 90 degrees. 
The transducer heads are mounted on a wheel which has an axis of rotation 
parallel to the longitudinal center line of the tape path, ad the 
transducer heads rotate in a common circle or orbit, consecutively 
scanning transversely of the recording tape. The tape motion spaces apart 
the successive scans of the heads and the "wrap" of the tape around the 
transducer orbit is such that one head begins recording interface with the 
tape before the preceding head leaves the tape. Each head scans 
essentially the full width of the tape, and the angle of the scans with 
respect to the length of the tape is a relatively large angle, usually in 
excess of 60.degree. and closer to 90.degree.. This angle, of course, will 
vary with differences in velocities of tape movement and head rotation. 
Another form of scanner is commonly referred to as the helical scan, and it 
in turn is embodied in several different ways. In most cases the scans are 
at a much lesser angle to the tape length, such as between 30.degree. and 
60.degree.. For example, a single head is rotated in a circle or orbit, 
and the recording tape is wrapped around the mandrel or drum on which the 
head rotates, either with the drum itself rotating or the head rotating in 
a slot around the drum surface. The tape is wrapped completely around the 
drum (360.degree. wrap) and the single head thus produces successive scans 
at an angle across the tape. This angle will depend again on the relative 
head and tape velocities, and also on the diameter of the head orbit and 
the width of the tape, each of these being a factor in determining the 
helix angle at which the tape wraps around the drum. 
Another version of the helical scan recorder utilizes the so-called omega 
wrap, wherein the tape extends around the scanner drum or mandrel in a 
loop which is slightly open, a few degrees less than 360.degree.. Again, 
it is most common in this type of system to utilize a single head, and the 
scanner diameter, tape width, and the head and tape velocities are 
selected and correlated such that when used for television recording, this 
system normally scans at a rate such that one scan of the head at an angle 
across the tape corresponds in time to one field of video information. 
Another version of scanner utilizes a tape wrap slightly in excess of 
180.degree. and two diammetrically opposed heads, as in U.S. Pat. No. 
3,418,424. The heads transduce the same signal, and due to he wrap of 
slightly over 180.degree., there is a small amount of redundancy where one 
head leaves the tape and the other enters into interface with the tape. 
Scanners of this type have been proposed for single field recording, and 
in addition some such scanners have utilized a format where each scan 
occurs so rapidly that only a segment of any video field is recorded. In 
such instance the scanner system has been known in the art as the 
"segmented field" recorder and scanner. 
Various other scanner arrangements have been proposed utilizing three 
transducer heads instead of two, with a 120.degree. wrap, or four heads 
with a wrap slightly in excess of 90.degree.. Such scanners have been 
found, for example, in systems which were introduced to the commercial 
market, but have since been discontinued for one reason or another. 
As mentioned previously, some of these scanners utilize a rotating drum or 
wheel (the terms are often used synonymously, but larger diameter rotating 
members have also been called wheels), to carry the heads, while in units 
with smaller diameters the heads rotate in slots formed in stationary 
drums or mandrels. With a few exceptions, however, when a plurality of 
heads is used they have been arranged to follow the same orbit or circle. 
One exception to the common orbit scanner is a single field omega wrap 
scanner, disclosed in U.S. Pat. No. 3,188,385, where two heads are 
utilized spaced axially of the scanner as well as circumferentially. The 
circumferential spacing is non-uniform, one head lagging the other by an 
acute angle in the order of 8.degree. to 10.degree.. In video recording, 
one head receives the video information for an entire field, and the other 
head receives only vertical synchronizing information which is recorded in 
a separate path or track along one edge of the tape. These vertical sync 
scans are substantially lesser in width than the main scans on which full 
field information is recorded. 
Another exception is the skip field recorder such as disclosed in U.S. Pat. 
No. 3,588,378. There a single head is used to scan helically and record 
one of every three fields of a television signal. The scan extends the 
full width of the tape. Three playback heads are used, spaced 120.degree. 
apart. The head to tape relation is mechanically phase shifted from record 
position to playback position, so that each of the three playback heads 
tracks in sequence the same single scan previously followed by the record 
head. For this purpose, the playback heads are axially displaced a small 
amount, but the scanning helix angle is such that each of the heads scans 
fully across the tape. 
All of the above mentioned scanners, except the transverse scan quad 
format, require either a substantial change in elevation of the tape in 
passing around the scanner drum, or use of a rather large drum mounted 
with its axis of rotation at a small angle to the tape path. The 
transverse scan, of course, requires a semicylindrical forming of a 
longitudinal section of a wide tape, bending it generally about its 
longitudinal axis, and this presents increasing difficulties as narrower 
tape is used. As a rule, four inch wide tape is used with the transverse 
scan quad format. 
When change in tape elevation is encountered with narrower tapes (e.g., two 
inch or less) helical scan formats which use a smaller diameter and 
greater angle of scan, complex rollers, guides, etc., are required to 
control precisely the movement of the tape onto, around, and exiting from 
the scanner. 
Various proposals have been made for scanners which cooperate with a 
cartridge or cassette (the terms are sometimes used interchangeably) which 
provides a convenient mechanism for storing and handling the recording 
tape. A number of systems have become known commercially, as follows. 
The first system involves a two-head scanning wheel with mechanism that 
reaches into a cassette and withdraws the tape, forming the tape into a 
loop of more than 180.degree. around the scanner. Such a system is 
utilized commercially by a number of companies such as Sony, Phillips and 
JVC. 
A second arrangement, marketed by a company known as Cartridge Television, 
Inc., utilizes a scanning wheel with three heads. The tape is again, 
however, withdrawn from the cassette and formed into a turn of slightly 
more than 120.degree. around the scanning wheel. 
A third system, which has been proposed by companies such as Ampex and 
Matushita, involves the use of a cartridge with a single spool, having a 
free end of tape extending from the cartridge with a leader thereon, 
together with a self-threading mechanism that directs the leader and tape 
around a two head scanning wheel, wrapped in excess of 180.degree., and 
thence to a take-up spool which is separate from the cartridge. 
A fourth type of cartridge system was introduced by RCA, and utilizes a 
cartridge with an opening that can be uncovered in one of its edges to 
expose a span of tape, the space behind such span being somewhat open 
within the cartridge, and a four head scanning wheel. This is shown in 
U.S. Pat. No. 3,766,328. The cartridge is inserted around the circular 
periphery of the scanning wheel, such that the span of tape forms a turn 
within the cartridge contacting the scanning wheel over an arc slightly in 
excess of 90.degree.. 
All of the aforementioned cartridge (or cassette) systems, however, utilize 
rather large scanning wheels, having diameters in the order of six to nine 
inches, such that the tape wrapped around the scanning wheel is of 
considerable extent. 
SUMMARY OF THE INVENTION 
The present invention provides a novel recording format, a novel wide 
bandwidth magnetic recorder, and a novel scanning mechanism and method for 
such a recorder, together with several embodiments of recorder 
arrangements including a cassette version, in each of which embodiments 
the amount of recording media, e.g., magnetic tape occupies a 
substantially high percentage of the total volume of the recorder than has 
heretofore been possible. This, in turn, results in a recorder which 
provides maximum capacity for the space which it occupies. 
The combination of the novel format, scanner, and tape handling mechanisms 
of the recorder, provide a type of segmented helical scan system in which 
recording tape changes elevation only an insignificant amount, thereby 
providing a unit which has an unusually low total thickness. This is 
significant in a number of respects, including the provision of a 
relatively thin cassette in a wide band width recorder which is fully 
capable of color video recording. 
The scanner provided by this invention incorporates at least three, 
preferably four, simultaneously rotating transducer heads. These may be 
supported for rotation in a number of ways, but a most convenient 
arrangement is to mount the heads spaced equally around a rotating 
scanning drum, and also spaced longitudinally of the axis of rotation of 
the drum. The longitudinal and axial spacing of the heads, and the 
diameter of their orbits, are correlated to the angle which the scanner 
axis of rotation assumes relative to the longitudinal axis (and hence the 
path) of the recording tape, and to the angle of wrap of the tape around 
the scanner. The heads are spaced apart far enough in the axial direction 
that each head revolves in a scanning circle or orbit which traces 
separate helical scan paths longitudinally of the tape. In other words, 
the successive scans, or scanning paths, of any one head nevery occupy a 
position on the tape overlapping scans, or scanning paths, of the other 
heads. 
This results in a novel recording format. In the handling of television 
signals, for example, the scanner rotation and tape speed is selected such 
that each field is recorded in several scans of different heads, located 
in different paths along the tape, e.g., a new type of segmented field 
recording. The format is, of course, useful also in other recording than 
television. 
It is possible to arrange the circumferential and axial spacings of the 
heads such that any redundant information occurs where the scan paths are 
adjacent, rather than nearer to the edges of the tape where it is possible 
that head to tape contact might at times not be consistent. 
The scanner and format also provide a novel arrangement of head scanner 
interface which uses significantly less than 180.degree. of tape turn. 
Thus, a short length of tape can be exposed along a side of a cassette, 
and the cassette inserted only slightly around the scanner to achieve the 
necessary interface. It is not necessary to draw a loop from the cassette, 
nor to provide any complex guide rollers, etc., in the cassette which 
would require precision location to the scanner. The invention thus 
includes provision of a novel cassette type wide band magnetic recorder. 
In two forms of the system, one a reel-to-reel and the other a cassette 
version, the tape is guided and fed by a belt system, generally of the 
type disclosed in U.S. Pat. No. 3,305,186. This system is sometimes known 
as the Isoelastic Drive. It maintains the tape under complete control and 
proper tension at all times.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
FIG. 1 shows a length of recording tape 10 approaching a schematically 
represented scanner 12 which may be in the form of a drum 15 rotatably 
supported on a base 16. The axis of rotation 18 of the drum is located at 
a relatively small angle to a line perpendicular to the tape edges. Stated 
another way, the axis of rotation 18 is at a substantial angle, in the 
order of 80.degree., to the longitudinal center line of the tape and thus 
to the path of motion of the tape as it is transported to and around the 
scanner. 
A plurality of transducers, shown as four, 20, 21, 22, and 23, are mounted 
at the surface of drum 15. Rotation of the drum, as indicated by the arrow 
in FIG. 1, causes each transducer to follow a different orbit, due to 
their axial spacing along the drum. The tape is guided through a turn 
contacting the drum over a scanning field, represented by the area 25, 
which is such that each transducer scans repeatedly a separate and 
discrete part of this field. In the embodiment shown, the turn of the tape 
is about 96.degree., and the scanner drum diameter may be in the order of 
1.125 inches (286 mm), thus each transducer scans about 0.94 inch (2.387 
mm) on the tape, at an acute angle (about 10.degree.) to the tape length, 
along a separate independent track lengthwise of the tape. The change in 
elevation of an edge of the tape moving around the drum is about 0.160 
inches (0.406 mm). 
The four scan tracks are indicated in FIG. 1 at 30, 31, 32 and 33, and each 
contains a sequence of helically scanned recordings. Preferably there are 
narrow guard bands 35 between the tracks, and somewhat larger bands 36 at 
the sides of the tape for longitudinal recording of audio and/or control 
(e.g., servo) information. 
FIGS. 2, 3, and 4 illustrate the general arrangement of a miniature tape 
recording unit embodying the features of the present invention. Referring 
to FIG. 3, the unit comprises a generally rectangular housing 40 including 
a power and electronics package 42 in one corner thereof. This package may 
contain, for example, a drive motor 43 together with one or more 
electronic circuit assemblies (not shown) which provide the necessary 
circuitry for preamplification of head output, etc. With a unit of this 
small size, a multi-circuit output connection can be provided for 
connecting through a cable to a remote battery or similar power supply, 
and to power amplifier and other conventional circuits used with such tape 
recording devices. 
Mounted in the housing 40, on a deck surface 44, is a take-up spool 45 
having one end of the tape 10 fastened thereto, and a supply spool 47 
mounted in spaced relation to the take-up spool 45, and having a quantity 
of the tape wound thereon. In FIG. 3, the supply spool 47 is shown full of 
tape, illustrated in solid lines, and the take-up spool 45 is shown empty, 
its diameter indicated in solid lines. The dot-dash lines indicate the 
diameter of a full take-up spool. It will be noted that there is some 
overlap of the full diameters, however, as one enlarges the other 
decreases such that there is no interference in fact. 
Tape is transported from the supply spool to the take-up spool by the 
motion of a driving belt 50 which may be of the type disclosed in the 
aforementioned U.S. Pat. No. 3,305,186. This belt extends around a power 
driven capstan 52 and around four guide rollers 54 which guide belt 50, as 
shown in FIG. 3, around the tape on each of the spools, into the space 
therebetween, and back to the drive capstan 52. Thus, constant speed 
rotation of capstan 52 produces a constant velocity movement of the 
driving belt 50, and it in turn advances the recording tape 10 at a 
constant velocity. The tape 10 leaves the supply pack on spool 47 and 
passes around a pair of guide rollers 56, thence around a pair of flanged 
straightening and guiding posts 58 and 60, then to a further guide roller 
62 and on to the take up spool 45. The scanner 12 is mounted between the 
guiding posts 58 and 60, such that a turn of the tape 10, as previously 
explained, wraps around a portion of the surface of a rotating scanner 
drum, in the order of 96.degree.. 
FIG. 2 illustrates a suitable construction of the scanner drum. The 
mounting block 70 is arranged with a lower surface 72 adapted to be 
supported on the deck surface 44. A hollowed out upper surface 73 is 
constructed at the precise angle of inclination desired for the axis of 
rotation of the scanning drum, for example, 80.degree. from the horizontal 
surface 72. The central portion of the mounting block 70 is provided with 
a bore which receives a spindle 75, this spindle extending upwardly beyond 
the surface 73, and being provided with a bore which receives a spindle 
75, this spindle extending upwardly beyond the surface 73, and being 
provided with a cap 76 at its upper end. The central part of the upper 
block surface 73 is provided with a cavity 78 containing a rotary 
transformer 80, parts of which are later described. 
The drum structure itself is comprised of a central cylindrical hub 82 and 
a plurality of disc members 83, 84, 85 and 86 stacked together and fitted 
to the hub 82. Inside the hub, upper and lower ball bearings are fitted, 
with these bearings indicated generally by reference numerals 88 and 89, 
the inner races of these bearings being fitted to support spindle 75, with 
the inner race of the upper bearing 88 precisely located with respect to 
the spindle cap 73 by one or more shims 90. 
A drive pulley 92 is fastened to the cap 76, and a retainer ring 94 is 
bolted to the undersurface of the lower disc 86, and is fastened to the 
rotating part 80a of the rotary transformer. The stationary part 80b of 
that transformer is fitted around a central part of the block 72, in order 
to provide the required rotary coupling for the output signals from the 
respective heads. Each of the heads 20-23 is fitted to one of the rings 
83-86, the lowermost head being shown in FIG. 2, and these heads being 
spaced around the scanner assembly 90.degree. apart, in the case of the 
four-head arrangement shown. The drive for the scanner drum is provided by 
a belt 95 which extends around the pulley 92 and to the output pulley 96 
of the drive motor. 
FIGS. 5 and 6 show another form of recorder in accordance with the 
invention, wherein the tape holding and handling mechanisms are provided 
in the form of a cassette, separate from the deck which mounts the 
scanner, the scanner drive, the final tape guiding posts, and the drive 
for advancing the tape. 
The plan view of the deck 100 shows the drive motor 101 driving pulley 102 
which is coupled via belt 103 to a pulley 104 attached to the shaft of the 
scanner assembly 105. This assembly is of the same type as shown in FIG. 
2. The belt 103 also passes around an idler pulley 106 and to a speed 
changing set including the pulley 107 and output pulley 108 which in turn 
is connected via belt 109 to the tape drive pulley 110. It in turn, drives 
a capstan 115 which is journalled in the deck and operates, as later 
described, to advance the tape. On opposite sides of the scanner assembly, 
there are mounted primary straightening and guide posts 120 and 122 which 
function to guide the recording tape 125 precisely onto and off the 
scanner assembly. 
A protective cover (omitted from FIG. 5) may extend over the scanner 
assembly as well as the capstan and guide posts which are accessible 
within the cassette receiving area 126. The drive motor and the above 
described pulleys and connecting belts are all housed within the deck. 
The plan view of the cassette 13 shows the supply spool 132, carrying a 
full pack 134 of tape 125. Recording tape leaving the supply pack passes 
around a pair of end guide rollers 135, over a tension roller 137, which 
is carried on the end of a pivoting arm 138. The arm is spring-loaded by 
suitable spring (not shown) to the position shown in full lines in FIG. 5, 
and can pivot under tension applied to the tape, as subsequently 
explained, to the position shown in FIG. 6. 
From the tension pulley the tape passes around the rollers 135 across an 
opening 140 at one end of the cassette. The opening 140 is somewhat 
greater in width than the space occupied by the scanner assembly 105 with 
respect to the edge of the cavity in the deck. The cassette, when 
withdrawn from the deck, has a span of the recording tape extending across 
this opening. From the exit post 135 the recording tape passes to a rewind 
guide post or roller 142, and thence around the take-up spool 145. 
The supply and take up spools are driven simultaneously by a drive belt 
system, which includes a tensioned drive belt 150 passing around the tape 
on the take up spool 145 and around intermediate guide rollers 152, then 
around the capstan backup or pinch roller 155, around the supply tape pack 
134, over a tension roller 156. The tension roller is carried on a 
spring-loaded pivoting arm 157. The belt passes from the tension roller to 
a guide roller or post 158, then to a secondary driving and guide roller 
160, and back to the take up spool 145. 
The pinch roller 155 and the secondary drive roller 160 are connected by a 
belt 162, on the opposite side of the cassette body from the supply and 
take up spools. The diameters of rollers 155 and 160 are so related (as 
explained in U.S. Pat. No. 3,305,186) that, in conjunction with the 
tensioning roller 156, the belt is kept under tension which is reflected 
to the entire length of tape from the supply spool to the takeup spool. 
Thus, when the cassette 130 is inserted into the cavity of the deck, the 
free span of the recording tape is drawn around the scanner 105 and into 
contact with the primary guide posts 120 and 122, precisely locating the 
recording tape with respect to the scanner. At the same time, the capstan 
115 engages the drive belt 150 at the pinch roller 155. When the motor is 
energized it rotates the scanner at the desired speed, and also, through 
the capstan and the drive belt, rotates both the supply pack of recording 
tape and the take up pack (clockwise as viewed in FIG. 5). The take up 
pack gradually enlarges as recording continues, thereby moving the 
recording tape past the scanner at a constant velocity, which is correctly 
correlated to scanner rotation. As the cassette is inserted and the free 
span of the recording tape is drawn around the scanner assembly and the 
primary guide posts, the arm 138 pivots, carrying the tension roller 137 
with it, thereby accommodating the change in tape path. 
FIG. 7 shows the same scanner assembly incorporated into a reel to reel 
tape deck. The same reference numerals with suffix a are applied to like 
parts. The location of the supply 132a and take-up 145a are reversed. The 
take-up is driven via belt 162a, and capstan 115a is on an idler set which 
also drives the belt which is tensioned as necessary by the roller 175, 
link 176, and tape tension sensor 177. The drag member 180 and arm 182 
react from tension sensing roller 184 to keep the correct drag resistance 
on supply 132a. 
While the method and forms of apparatus herein described constitute 
preferred embodiments of this invention it is to be understood that the 
invention is not limited to these precise method and forms of apparatus, 
and that changes may be made therein without departing from the scope of 
the invention.