CA1083257A - Rotating head recorder with different recording and playback speeds - Google Patents

Abstract

ROTATING HEAD RECORDER WITH DIFFERENT RECORDING
AND PLAYBACK SPEEDS

Abstract Of The Disclosure A recording and reproducing system capable of recording at one speed and playback at another speed in-cludes a capstan linear drive for a tape, and a headwheel drive means to drive heads in a transverse direction over the tape. Recording and/or playback is accomplished at any speed within a first given two-to-one speed range by operating the capstan linear drive at a corresponding speed, and by operating the headwheel at a speed which has a first given constant ratio with the linear speed. Recording and/or playback is accomplished over a second different adjacent two-to-one speed range by operating with the capstan linear drive at a corresponding proportional speed, with the headwheel at a speed which has a second different constant ratio with the linear speed, and with the rotating headwheel physically tilted by a given small angle relative to the transverse direction.

Description

- RCA 70,779 ,.:
Backgroun~ Of The Inv_ntion -~ -A magnetic recording system widely used for recording television vi~eo and audio signals and used also for digital signals, is called the quadraplex system and it ~-involves a magnetic tape about two inclles wide which is driven past a transversely rotating headwheel carrying four equally-spaced magnetic heads. The heads move across the tape at right angles witll the direction of linear movement of the tape, and each recorded track or path on the tape is at an angle ~ on the tape with the directlon of linear movement of the tape. The angle ~ ~epends on the speed each head goes transversely across the tape relative to the linear speed of the tape. The transverse and linear speeds used for recording are used also for playback to insure that .. .
the heads will follow the recorded tracks at the angle ~.
; It is sometlmes very desirable,~particularly wlth ` ~-di~gi~tal~signals, to be able to record the signals at one speed and play back~the slgnals at anot~herhigher or~lower speed.;~
~ ; Summary Of The Invention~
A rotating head recording system in which recording an~d playback can be at different speeds over a limited range -~
of~speeds, such as~two-to-one, by main~taining a constant ratio between the transverse speed of the heads and the Iinear speed of the tape. Recording and playback can be at dlfferent speeds over a large range o~speeds by changing -,:
the ratio of transverse to linear speeds, and slightly ; ;
altering the angle the headwheel makes with the linear direction of the tape.

,~

-2-I~CA 70,779 !

1C~83Z57 1 Brief Descri~tion Of 1`he Drawing FIG. l is an elcvation of a rotating head recorder constructed according to t]1C teachings of the invention;
FIG. 2 is a vie-~ looking in the dircction 2 at the headwlleel in the recorder of FIG. l;
IIG. 3 is a diagram illustrating the effect of transverse head speed and linear tape speed on the angle .
of the tracks on the recording tape;
FIG. 4 is a block diagram of a servo system for con-trolling the speed of the headwheel and the speed of the ::~ recording tape in the apparatus of FIG. l;
1IG. 5 is a chart from which one can select the con~ditions for recording signals at any desired speed, and select the condit1ons for playback of the signals at any ~ ;
:15 other desired speed;
FIG. 6 is a tabulation of headwheel tilt angles for:~the six reg1ons 1n the chart of F1G. 5;
IG. 7 is a series of charts which will be referred t~o ln describing the operation of the~apparatus:in FIG. l ::20 :: when operated to record signals at a given high speed, and to playback the recorded signals at selected slower sp~eds;
and FIG. & is a diagram which will be referred to in :~
:descr1bing the reason for tilting the headwheel when 2S recording or playing back at certain data rates~
: Description:Of The Preferred Embodiment ~ .
-~ Referring now 1n greater detail to FIGS. l and 2, the rotating head type recording apparatus shown includes a base lO supporting a magnetic tape supply reel 12 and motor 13, and a tape take-up reel 14 and motor 15. A .

RCA 7 0 , 7 7 9 magnetic tapc l.6 extending between reels 12 and 14 is about two inches wide and is ~Iriven by a capstan 18 between idler rollers 17 and 19. Thc capstan 18 is driven by a capstan motor 20.
A headwheel platform 22 has an end 23 mounted at 24 a fixed distance above the base 10. The other end 25 of the platform 22 is connected by a link 26 to an eccentric connection 28 on an adjusting wheel 30. The wheel 30 is rotatably mounted at 31 on a bracket 32. The wheel 30 has I0 a knurled edge at 33 to facilitate its manual rotation ~.
for the purpose of moving the link 26 to cause the end 25 of platform 22 to pivot about its end 23 fixed to the : base 10. The periphery of wheel 30 is provided with notches 34 for engagement by the end of a spring-loaded pawl 36 ~;
to provide detents for six predetermined positions of the wheel 30 and the platform 22. --~
The platform 22 carries a headwheel motor 40 having a headwheel 42 on one end of the motor shaft, and having a tone wheel 44 on the other end of the motor shaft. A ~ -~: 20 vacuum tape guide 46 ispositioned on the side.of the magnetic tape 16 opposite from the headwheel 42 to give the ~; ; tape an arcuate shape corresponding with the peripheral surface of the headwheel. The headwheel carries four magnetic Ileads 48 which scan across the magnetic tape in : . .
~: 25 a~direction at right angles to the direction of linear .. ~.. -~: tape motion. The tonewheel 44 cooperates Wit}I a fixed .~
pick-up 49 in a usual manner to constitute a tachometer providing a si~nal indicative of the speed of rotation o .
the headwheel 42.- :
A control magnetic head 49'is positioned at one ., ' . '~ ` .' '.

RCA 70,779 edge of the magnetic tape 16 for the purpose of recording and playbac~ of a tape servo control signal for insuring in-phase registration of transverse scans over recorded tracks during data playback.
FIG. 3 shows magnetic tracks 50 made on a tape 16 by the combined rotation of the ~adwheel 42 and the capstan 18. The tracks 50 make an angle ~ with the linear direction of motion of the tape. The angle ~ is determined by the ratio of the transverse speed VT of the heads across the tape and the linear speed VL of the tape. The heads must follow paths 50 on playback at exactly the same angle as the paths followed during recording. This condition is satisfied by the present apparatus even though the playback speed is greatly different from the recording speed, FIG. 4 shows a servo system form~int~ining the ~ .
headwheel motor 40 and the capstan motor 20 at speeds necessary for recording at a desired data rate and for playback of the recorded data at a desired data rate.
Operation at a desired data rate, whether for recording or reproducing, is determined by a scan clock oscillator ~not shown) having a frequency variable between 20 and 10 ~H7.
~ .
The scan clock signal is applied at 54 to a known sub-synchronous power servo drive for three phase motor operation 25~ ~of the headwheel motor 40. The headwheel motor 40 is driven ~ .
by a motor driver 56 which is supplied with three-phase power from a generator 58 producing frequency which causes the motor to rotate at a rate about 50 per cent higher than the desired rat~. A frequency and phase detector 60 -supplies an error slgnal to the motor driver 56 to cause ~- :

RC~ 70,779 the motor to rotate at the desired spee~. The frequency and phase detcctor generates the error signal by comparing a reference frequellcy signal divided down from the scan clock frequcncy with a frequency derived from the tonewheel 44 and representing tlle actual speed of the headwheel. The headwlleel is thus made to rotate at a speed directly pro-portional to the scan clock signal applied at 54.
The right-hand side of FIG. 4 shows a servo system for maintaining the speed of the capstan motor 20 at a constant, but adjustable, ratio with the speed of the head-wheel motor 40. The headwheel motor speed indicated by the frequency signal from the tonewheel 44 is applied to an adjustable divider 62 which divides the frequency by 2N 1 , 1,2,4,8,16 or 32 in dependence on an N input at 64 of 1,2,3,4,5, or 6, respectively. The six values N represent six regions of operation which will be described in connection wlth FIG. 5. Each successive region has a transverse/
near speed ratio double that of the preceding region.
; ~ The capstan servo system on the right-hand side of .
~ 20 FIG. 4 also includes means operative during recording to ~ `
:
record a control track along one edge of the tape 16 and means operative durlng playback to insure that the magnetic heads will sweep paths phased with the recorded transverse tracks, rather than between the recorded tracks. For this purpose, the tonewheel frequency signal divided by 2N 3 from divider 62 is applied over line 66 to a control track .~ .
` recording circuit 68 and through a switch 70 to the cnntrol ~- `
head 49 on the tape 16. This causes the recording of a capstan servo control signal appropriate to the operating region N which marks the positions of the transverse scan .

~ . : - - : .
- . . .. .. . . .

RCA 70,779 tracks on tlle tape 16.
During this timc that data and a servo control signal are recorded on the tape 16, a switch 72 completes a loop 74 from and to a frequency and phase detector 76, whereby to produce at 77 a capstan reference frequency having a desired subharmonic or harmonic relationship with the tonewheel frequency representing headwheel speed. The capstan reference frequency at 77 is applied to a frequency and phase detector 80 which also receives a signal from a IO capstan tachometer 82 via a tachometer amplifier 83. The capstan error signal produced by frequency and phase detector 80 is applied to a motor driver 84 which supplies electric power to the capstan motor 20. The capstan 20 is driven at a speed such that the linear speed of the magnetic tape bears a fixed ratio (determined by operating region N) with the transverse speed of heads across the tape 16.
When it is desired toplay back the data recorded on the tape, the switches 70 and 72 are placed in their playback positions P. Then the servo control signal recorded ~ on an edge of the tape is read from head 49 through switch 70 to a playback servo control clrcuit 86, from which a signal lS applied through switch 72 to one input of frequency and phase detector 76. The error output of detector 76 is translated in frequency to a capstan reference signal at 25 ~ ~ 77 which is applied to the frequency and phase detector 80 where it is compared with the capstan tachometer signal. The capstan error signal from detector 80 is applied through motor driver 84 to the capstan motor, The capstan motor is driven at a speed such that the linear speed of the magnetic tape bears a fixed ratio ~determined by thecperating region ~.... . .
. . . .
. , .
- - . .' . .. : ,...... ;

RC~ 70,779 N) with thc transverse speed of heads across the tape 16, and tile transverse scan~ are positionally phased in regis-tration along the linear ~imension of the tape with the previously recorded tracks.
FIC. 5 shows the operating conditions of the described illustrative apparatus for a range of recording and playback speeds from 40 megabits per second to 0.625 megabits per second. At the highest data rate of 40 megabits per second, the headwheel is operated at 305 ~ ,;
revolutions per secnnd ( a point on the head speed curve 90), the capstan is operated to provide a linear tape speed of 20 inches ~50.8 cm) per second ~a point on the linear tape speed curve 92), and the headwheel 42 is positioned by adjusting wheel 30 so that the~eadwheel rotates in a plane which is at exactly 90 degrees with the direction of linear movement of the tape 16. Under these conditions, the relative speeds of the transverse and linear motions cause the heads on the headwheel 42 to sweep paths 50 shown in ~ :`
~ , ~ FIG. 7a at an angle Q with the linear dimension of the ~
~, :
tape 16. Data recorded under these speed conditions can, of course, be played back under the same speed conditions.
If the data recorded at 40 megabits per second is `
desired to be played back at half speed, at 20 Mb/s, the speed of the headwheel is halved to 152.5 rps, and the ~ `~
linear speed of the tape is halved to 10 ips. The paths `
followed on the tape by the heads are at exactly ~he same angle ~ during playback ~FIG. 7b) as during recording (FIG. 7a). It is also true as indicated on FIG. 5, that data recorded at any speed between 40 and 20 Mb/s can be played back at any other speed between 40 and 20 Mb/s. It is merely ; . - . - . -~,. ;. .. -.: . .

"I~CA 70,779 necessary to maintain a constant ratio between the headwheel syeed ~curve 90) and tl~e capstan spee~ (curve 92), i.e., the transverse spee~ V.l ~nd the linear speed VL. The speeds at W}liC]I recording and playback are performed are determined by proportional frequencies of scan clock signals applied at 54 to the servo system of FIG. 4, and the constant ratio between headwheel and capstan speeds is maintained by the servo system so long as an N=l signal is applied to the servo system.
loPlayback as described can be at any speed down to about one-half of the recording speed before the speed of the heads over the magnetic tape surface gets so slow that ~ -the induced voltage equal to d~/dt is too low to reliably reproduce the stored information. If the difference lS between recording and playback speeds is greater than a two-to-one ratio, playback can be accomplished by approp-riately reducing the line~ar~tape speed (curve 90) while malntaining the headwheel speed sufficiently high Ccurve 94) to~plck up the recorded lnformation and be at a speed which 20 ~ produces two transverse scans o the tape for every one -"
recorded scan. For example, referring to FIG. S, data; `~
; recorded at 40 Mb/s can be played back at 20 Mb/s by using a headwheel speed of 305 rps and a linear tape speed of lO~ips, and an~input N-2 to the servo system o~ FIG.`4.
; 25 ~. :Then, as shown in F~IG. 7c~, there are tw~o pIayback scans per recording scan, and the angle ~ remains substantially ; the~same a~s during recording. The angle ~ is made exactly the same as durlng~recording by tilting the plane of the headwheel from 90 degrees to 89.6594 degrees relative to 30the direction of linear tape motion. This is done by g , : . -- RCA 70,779 1~83ZS7 1 turning the a~justing ~ eel 30 to a next adjacent detent position. ;
In ad~ition to the playback described at 20 Mb/s, the record~d information can be played back at any rate from 20 Mb/s to lO Mb/s by merely changing the input scan clock signal applied to at 54 in FIG. 4 so that the head speed 94 and tape speed 92 have values corresponding with the desire~ data rate in Mb/s. At a data rate of lO Mb/s the conditions are as shown in FIG. 7d. ~
If an even greater reduction in playback speed is ; ~' desired to a rate between lO Mb/s and 5 Mb/s, the scan ` -, clock signal is cllanged to a value producing speeds along ~ ~-curves 96 and 92 corresponding with the desired data rate, the signal N is changed to N=3, and the headwheel tilt ~ -angle is changed to 89.4892 degrees. FIGS. 7e and 7f ;- -show two examples at the ends of this third data speed range. In this case there are four ~2N l) playback scan lines for each record scan line. Solely, the signal pickup `~
during the one playback scan going over the recording track is utilized. In a similar manner, even lower playback rates can be obtained at speeds where N-4, N-5, and N~.
FIG. 6 tabulates the headwheel tilt angles employed in ~ . :
each of the six speed regions N=l through N=6.
Recording may be a* any data rate shown in FIG. 5, and playback also~may be at any data rate shown. The headwheel tilt angle used during recording and during playback must be set to a value appropriate to the rate .
. ~ .
at which data is recorded or played back as indicated in FIG. 5. The various headwheel tilt angles differ by very small amounts, but the use of an indicated tilt angle in . . - .. , . , . , , , -RCA 70,779 I the exemplary apparatus is necessary for optimum operation of the apparatus at very high information packing density.
For an explanation of tlle reason why headwheel tilt angles are important, reference is made to FIG. 8 where line 100 represents a recording scan line across the magnetic tape 16 at an angle ~. If the headwheel speed is doubled so that two scan lines are used during playback without any change in the linear tape speed, the two playback scan lines may be as shown by lines 102 and 104, which are necessarily at an angle ~1 different from ~. To make the playback scan line occur at the same angle ~ as the recorded tracks, it is necessary to tilt the head~heel an amount ~2 which is approximately equal to one-half of the angle 90-~. When this is done, one of the two playback scans can be made to exactly follow the one recorded track. The ~-signal picked up durlng the one registered playback scan ~ is selected to the excluslon of signals occurring during r~ the unregistered playback scan~by appropriate utllization ; electronic apparatus not shown.
~ ~ While recording at a high data rate and playback st a low data rate has been described, it will be understood al$o that recording can be at a low data rate with playback at a high d~ta rate. ~It~will also be understood that the data~rates, headwheel speeds~;, number of heads per headwheel, capstan speeds, spe~ed ratios, and tilt angles herein described are glven solely by way of~example, and that other suitable values may be selected and em~loyed by those skilled in the art.
` ' ' ::

'

Claims (3)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A recording and reproducing system capable of recording data at any data rate within a wide continuous range including a plurality of N successive 2-to-1 sub ranges, and playback at any data rate within the same wide continuous range, comprising:
linear drive means to drive an elongated recording medium in a linear direction at any selected speed in a continuous range including a plurality of N successive 2-to-1 sub ranges, transverse drive means to drive heads on a rotating headwheel over the recording medium in a transverse direction at any selected transverse speed in one 2-to-1 speed range, speed control means responsive to a speed control signal for any data rate within a first given sub range where N equals 1 to operate said linear drive means at a corresponding speed, and to operate said transverse drive means at a speed which has a constant ratio K with the linear speed, whereby at all speeds in said first given sub range each head follows a path across said medium having the same angle .theta. with the direction of linear motion of the medium, said speed control means being responsive to a speed control signal for a data rate within a second different sub range of speeds where N is equal to 2 to operated said linear drive means at a corresponding speed proportional to the data rate, and to operate said transverse drive means at a speed which has a constant ratio 2K with the linear speed, and RCA 70,779 (claim 1 continued) means operated before recording or reproducing at a data rate in said second sub range to physically tilt the plane of said rotating headwheel through a given angle relative to the transverse direction to a position such that at speeds in said second different sub range each head continues to follow a path across said medium at said angle .theta. with the direction of linear motion of the medium.

2. A system as defined in claim 1 wherein said given angle is substantially equal to one-half of the angle 90 - .theta..

3. A recording and reproducing system capable of recording data at any data rate within a continuous range including N 2-to-1 sub ranges, and playback at any data rate within the same continuous range, linear drive means to drive an elongated recording medium in a linear direction, transverse drive means to drive heads on a rotating headwheel over the recording medium in a transverse direction, means to adjust the plane of rotation of said head-wheel to N progressively slightly different predetermined transverse tilt angles corresponding respectively with said N sub ranges, so that each head always follows a path across said medium having the same angle .theta. with the direction of linear motion of the medium, and speed control means responsive to a speed control signal for any selected data rate within the continuous range to operate said linear drive means at a corresponding speed, and to operate said transverse drive means at a speed having a ratio NK with said linear speed, where K is a constant and N is the sub range of the selected data rate.