CA1127295A - Servo control apparatus - Google Patents

Abstract

SERVO CONTROL APPARATUS

ABSTRACT OF THE DISCLOSURE

Servo control apparatus for controlling the speed and phase of a driven member. Reference signals, having a frequency determinative of the speed at which the member is driven, are compared to actual speed-representing signals in a servo loop, whereby the member is driven at the speed determined by the reference signals. An actual position-representing signal, representing the position, or phase, of the driven member, is derived. A window pulse generator generates window pulses corresponding to desired positions of the driven member. The occurrence of these position-representing signals within the duration of the window pulses is detected. A frequency modulat-ing circuit modulates the frequency of the reference signals if the position-representing signals occur outside the window pulses, so as to adjust the speed and position, or phase, of the driven member until this member is driven such than its actual positions correspond to the desired positions. In accordance with a further aspect of this invention, the phase of the reference signals is adjusted such that the position-representing signals occur at a predetermined location within each window pulse. The driven member can be a rotary transducer or a movable record medium in, for example, a video signal recording/reproducing system.

Description

~ ~ ~27~5 BACKG~OUND OF THE INVENTION
This lnvention relates to servo control apparatus and, more ~articularly, to such appara~us which finds ready applica~
tion in a video signal record-~ng/repxoducing system, where~y the driven member, which may be a xotar~ transducer ~or t~e movable record medium, has its speed and phase contxolled ~n synchronism with the horizon~al and vertical synchronizing signals included in the ~ideo signal.
In a video signal recording/reproducing system, such as a video tape recorder (V~, a transducer, such as a rotary magnetlc head, scans the record medium, such as mag~etic tape, as the medium is mo~ed. I~ the VT~, vldeo s~gnals are recorded on the head in parallel, skewed record tracks; and these vides slgnals subsequen~ly are reproduce~ to result in a corresponding video picture. For improved quali~y in a VTR, either ~or use in television broadcast applications or for home entertainment~ ~he rota~ion o~ the magnetic head and/or the movement o the tape should be synchronize~ with external s~nchronizing signals~ That is, and wit~ xespect to t~e rotary head, ~or exa~pl~, t~e rotational ~0 speed of the head, as well as its phase, or position, shou~d be.
synchronized. Wit~ respec~ to the tape, w~ich generally is dri~en ~y a caps~an, t~e spee~ and pos~tion of that tap~ like~ise ~should be synchronized.
In one type o synchronizing control apparatus, known as servo control apparatus, for controlling the rotary speed and posit~sn of the ma~ne~ic head~ the speed is controlled ~y one servo loop and the position is controlled ~y anot~er. For exæmple, a frequency generator, suc~. as a m~gn~iG-~oothed wheel and a mag-netic pick-up, i5 provide~ on or driven ~t~ the ~haf~ w~ch dr.~es the rotary magnetic h~ad. The fre~uency of the signal produced by .~ 1 ~

~:~Z7~2~15 this frequency generator is a function of the rotary speed o~
the head. This ~requency is compaxed ~ith a re~er~nce ~r~quenGy, such as the frequency of a signal derived ~rom the horiæontal synchronizing signal included in a video signal, and any dLfex-ence there~etween is used to adj U5~ the speed at which the headis driven. In the pos~tion-control servo loop, a pos~tion pulse generator, such as a magnetic element secured to the rotary head drive-shaft and a magnetic pick-up, generates a position pulse each time that ~he head rotates into a predete~mine~ position ~ith respect to the tape, suc~ as into initial magnetic co~tact with the tape. The posi~ion pulse is phase-compared to thP
vertical synchronizing signal included in the video sisnal; and any phase difference therebetween is used to ~riefly change the speed of the head so as to adjust its phase. The two servo loops cooperate first ~y adjusting t~e phase of the rotary head to within a predetermined desired range, and then to con~rol the ro~ar~ speed while maintaining the phase wit~i~ t~is desired range.
How~er, since the speed and phase control of the afore-mentioned servo control apparatus requires the use of t~o separate and independent servo ~oops, th}s appar~tus is o~ xelative:Ly com-plex construction. Furt~ermore, if the gain of the phase :ontrol servo loop is large so as to lim~t t~e`accep~a~le ra~ge o~ desired position, hunting o~ten occurs whexe~y the p~ase of t~e rotar~
head overshoots and unders~oots, i~e. r hunts, a~out ~s desired, ~5 limited range. Conversely, if the gain o~ the phase contral ser-vQ
1QP is reduced so as to avoid such undesired hun~i:ng ~ it may re~uir~ a long time delay until proper phasing, or posi~ioning, ~f the head is attained . These factors must be ta}cen ; nto accourlt in designing servo contxol apparatus, thus making t~.e design o:E
30 ~uch apparatus quite ~ifficult~
., .

-2~

~1 ~272~5 ~BJECTS OF THE INVENTION
Therefore, it is an o~ject o the present inven~ion tQ provide impxoved servo control apparatus which avoids the aforenoted pro~lems attending prior art appara~us, and which i~
of relatively simple construction, low in cost and small in siæe.
Another object of this invention is to provide improved servo control apparatus for controlling the speed and posi~ion of a driven member, and wherein t~e positioning of that mem~er is at~ained rapidly within a desired range without undesired over-shooting and undershooting of that range; and without requiringan unde~ired lon~ delayed time in attaining the proper positioning of the driven member.
A further o~ject of this invention i~ to provide improved ser~o control apparatus which utilizes digital techniques lS for high accuracy and speed.
An additional object of this inven-~ion is to provide servo control apparatus for use in a ~ldeo signal recording/reproducing system of the tvpe wherein a rotary transducer scans across a mov~ble record medium, and wher~n the position o the transducsx relative to the medium is synchronized with the vertical synchroniz-ing si~nal of t~e video signal.
Yet another o~ject o thi~ invention is to pro~ide servo control apparatus of the aforedescribed type wherein the position of the h~ad or meaium is controlled to be -~ithin a pre~
~5 d0termined limited ran~e at the time of occurrPnce o the vertical synchr~ni~ing signal.
A s~ill further object of this invention is to pxovide servo control appar tus of the aforementioned type whexein the position of th~ he~d or medium, once wïthin the pred~termined rang~
is adjustable so as to correspond to a predetermined locatlon at the ~2~:9S

time of occurrence of the vertical synchronizing signal.
Variou~ other objects, advantages and features o~ the present invention will become ~eadily apparent ~xom ~h~ ensuing detailed description, and the novel features will ~e particularly pointed out in the app~,nded claims.
SUMMARY OF TH~ INVENTION
-Ir. accordance wlth this invention, s~rvo control apparat-~s is provided for con~rolling a dri~en membex, such as a rotary trans-ducer or a movable record medium used in a video signal recording/
reproduclng system. S~gnals rspresenting the ac~ual speed a~ ~hich the motor is driven are derived, and these signals are compared to a sourc~ of reference signals having a frequency determinative o the speed at which the mem~er is to ~e driven. The re~erence signals may be synchronized w~th the horizontal and vertical synchronizing signals included in a viaeo signal. A single servo loop is provided for driving the mem~er~ ~he speed at which the membex is driven ~ei~g varied in accordance wi~h any phase differ-~ntial between the reference s~gnals a~d tha speed-repres~nting ignals. Signals represanti~g the actual position of the driven mem~er also are derived; and these position-representing signals are compared to ~;~ndow puises which correspond to desired positions of the driven mem~er~ In the even~ that the position-repr~senting signals occur outside the window pulses, the frequency of the reference signals i5 modulated so as to adjust the.speed and posi-tion or the driv~n member until the actual posit~.Qn of that me~bercorresponds to the desired po~ition. In accordance with one asp~ct of this invention, the phase of ~e r~erence signals is adjusted once the posi~ion-representins signals occur within the window pulses, so as to fur~her ad~ust ~he position of the driYen member, where~y ~he positior.-representing signals occur at precise, ~7Z~35 predetermined locations wi~hin the window pulses. In ~his manner, the position o.~ the rotary transduce~ rela~ive ~o ~h~
record medium ls synchronized to be at a desired location at the tlme of occurrence of, for ~xample, the vextical synchroniz-ing signal of the video signal.
. .
E~RIEF DESCRIPq~ION OF T~IE DRAWINGS
The following detailed description, given by way o ;~ example, will ~est be understood in conjunc~on with the accom-panyin~ drawings in whic~:
FIG~ 1 is a partial ~lock, partial logic diagram of one embodiment of the present invention;
FIG. 2 is a ~lock diagram of an alternative embodiment of this invention;
FIG. 3 is a graphical representation of the phase differ-ence between an actual positlon-representing pulse and a refer~nce position pulse, such as a vertical synchroniz.ing signal, and the error voltage produced ~y a p~ase comparator as a result of t~is phase difference;
FIGS~ 4A-4M are waveform d;agrams which are useful in understanding the operati`on of t~e em~odiment show~ in FIG. l;
FIGSo 5A-SI are additional waveform diagrams whic`h are useful in unders~and~ng the operation of this em~odiment;
FIGS. 6A-6F are wz~e~orm diagrams w~ich are use~ul in understanding the operation o~ ~e embodiment sho~m in FIG. 2, and FIGS. 7A-7~ are waverorm di~grams represent;ng diffe~ent operations or the ~mbcdiment shown in FIG. 2.

--S--~21~Z~5 DETAII~ED DE5CRIPTIOM OF CERTAIN PREF~:RRED EMBODIMhNTS
Re:ferring now to the drawin~s, ~herein like reerence numerals are used ~hroughout, FIG. L .illus~rates one em~od.Lment o servo control apparatus in accordance with the pre~nt inven-tion, which apparatus ~s used, for example, to control theposition of a rotary transduc~r, such as one or more rotary masentic heads, used in a video recording/reproducing system, such as a VTR. For ths purpose of explanation, t~e servo control apparatus is described in t~e environment of a VTR. However, it should be réadily appar~nt that the present invention can ~e use~
to control other members whic~ are driven in synchxonism ~ith reference signals such that the phase of the driven member is controlled. FIG. 1 illustrates a controllable motor 1 which is connected via a d.rive shaft to one or more magnetic heads and which serves to rota~e those heads at a con~rolla~le speed. A
frequency generator 2 is mechanically coupled to the drive shaft and is adapted to produce a signal whose fxequency represents the actual rotary speed o$ motor 1 and, thus, the actual rotary speed of the driven heads. As an e~ample, fxequency gensrator ~ may comprise a magnet-toothed w~eel which rotates with the dxive ~haft, and a magnetic pic~-up whic~ produces a pulse in response to the passage of each magnet~c tooth therepast. A num~er o~ such pulse~ is produced ~or each rotation of the drive qhart. Also secured to the drive shat IS a position pulse generator 3 which 25 is adapted to Generate a pulse r~presen~ing the actual position of the heads as such heads are ro~a~ed. As one example thereof, position pulse genPrator 3 may compx~se a magnetic element secured at a predekermined angular location on the drive shafk and a ma~netic pick-up wh~'ch generates a pulse ach time the magnetic elament rotates therepast. Depending upon the position of this 27~.S

magnetic element relative to the heads, position pulse gen~r~or 3 generates a position pulse that is disposed at a par-ticular phage when the heads ro~ate to a predetermined position.
The apparatus illustrated in FIG. 1 rurther includes a synchronizing signal separator 5, a phase locked loop 6, a control-lable frequency divider 10, a servo loop 11, a window pulse gen-erator 20 and a window detector 3~.. Synchronizing signal separator ; 5 may comprise a conven~ional synchronizing signal separator circuit and is connected to input ~erminal 4 to receive a video signal~
As is conventional, the ~ynchronizing signal separator operates to separate the horizQntal synchronizîng signal H~ and the.ve~tical synchronizing signal VD from the video signal which is 5uppl ied thereto~ The separated hori20ntal synchronizing signal HD de.r~ved from synchronizing slgnal separator 5 is ~upplied to phase locked loop 6 for locking the phase of higher frPquency reference pulse~
VN to the phase of the separated horizontal synchronizing signal.
The phase locked loop is comprised of a controllable osc.illator 7, such as a voltage controlled oscillator (VC0), a frequency divlder 8 and a phase comparat~r ~. The output of VC0 7, w~ich comprises Z0 higher requency pulses VN t is connected to frequency d_vi~;ier 8 which divides the freau~ncy of t~e higher frequency pulses by a pr~determined factor, suc~ as a divider ratio N~ The output of frequency divider 8 is conn~cted to one input of phase c~mparator 9, this phase comparator having another input connected to receive the separated horizontal synchroniz.ing signal HD~ D~pend.ing upon the phase differential de~ected by phase comparator 9 ~etween the divided pulses s-upplied thereto by frequency divider 8 an~ the horizontal synchroni~in~ signal, an error vol~age ~s suppl~e~ to VC0 7 to adjust the frequency of the VC0 and thus ~ring th~ phase o the higher fr2quency pulse~ V~ into synchronism with the phase ~L~2'~

of the horizontal synchronizing signal HD. As may be appreciated, the ~requency of the pulses generat~d by VCO 7 shoula be N ~imes the horizontal synchronizing frequency such kha~ phase comparator 9 is supplied with signals of e~ual ~requency.
The output of phase locked loop 5, that is, ~he higher ~re~uency pulses VN generated by VCO 7, is connected to controllable frequency divider 10 and, additionally, to window pulse generator 20. Controllable requency divider 10 may comprise a plural-stage count~r and is adapted to divide the frequency of the pulses VN supplied thereto ~y a predetermined factor M. Thîs factor M
may be increased ~o (M ~ 1~ or decreased to (M - 1), depending upon particular ratio control signals supplied there~o. For this purpose, controllable frequency divider 10 includes a first control input which, w~n supplied ~ith a xatio control pulse DU, reduces the di~i2er ratio from M to~11 . Controllable ~requency divider 10 includes another conkrol input for receiving a ratio control pulse DS, whereby the dlviding ratio of the frequency . .
divider is increased from ~ to ~ hese ratio control pulses are generated by ~indow detector 30, ~o be described.
~he output of controlla~le frequency di~ider 10 con-stitutes frequency-divided re~erence pulses C~, which are supplied to servo loop 11. The servo loop includes a phase comparator 1~, a drive circuit 13, motor 1 an~ frequency generator 2. The fre-quency-divided raference pulses CM are supplied to phase comparator 12 together wlt~ ~he sig~al ~G generated ~y frequency generator 20 It may be appreciated that ~he frequency o the sig~al FG repre-sents the actual speed of motor 1 and, there~ore, will ~e referred ; to herein as th~ speed-representing signalO 5erro loop 11 is adap~ed to adjust ~he spe2d of motor 1 such tha~ this motor is drirQn at the speed de~ermined by ~requency~divid~d referenee ~L~Z7~9S

pulses CM. In this regard, phase comparator 12 compares ~he phase o the frequency-di.vided referencé pulses to ~he phase of the speed-representing signal, and any phase di~eren~ial therebetween results in an error voltage which is applied to drive circuit 13. The drive circuit controls the speed o~
motor 1 in accordance with the magnitude a~d polarity o~ th~
error voltage. ~hus, the speed of motor 1 is controlled to be equal to that d~termined ~y t~e frequency of ~he frequency-divided reference pulses CM.
Window pulse generator 20 is adapted to generate a desired ~indo~ pulse ~a~ing a duration which establishes the range or the proper positionins of motor 1. That is, and as will be described in greater detail, this is t~e desired range during which a pos-ition pulse PG g~nerated ~y position pulse lS generator 3 should occur, Window pulse generator is comprised o~ counters 21, 22 and 23, ~istate circuits 24 and 25, and AND
gates 26 and 27. Each of counters 21, 22 and 23 includes a reset input connected to synchronizing signal separator 5 to receiv~
the separa~ed vertical synchron~zinq signal VD. Each counter also includes a clock input CK connected to the output of ~?hase locked loop 6 to receive t~e higher requency re~erence pu:Lse~ VN
generated by VCO 7. ~ach coun~er, after being reset to an initial - count, such as a co~mt of ~ero, is adapted to co~nt eacfi pulse supplied to ~he clock input CK thereof. Counter 21 ge~erat~s an output pulse CA after a predetermined num~er of hlq~r frequency pul~es VN ha~e ~e~n counted thereby. For example, if it is ~nown that a certain num~er x of refer~nce pulses VN are generatzd during each f ield inter~al of the video signals, that is, during the interval between adj acent vextical synchronlzing slgnals VD, counter 21 is ad~pted to CO~lt X/2 of these pulses. Hence, output ~7~3S

pulse CA is generated appro~imately midway between adJacent vertical synchronizing signals VD. Counter 22 i5 adapted to count another p~edetermined number o~ higher ~requency re~erence pulses VN. As a numerical exam~le, this counter coun~s 1,043 such pulses to produce an output pul~e CB. Coun~er 23 also is adapted to rount still anot~er prede~ermined number of high~r frequency reference pulses VN, for example, seven such pulses, to produce an output pulse CC.
~ Bistate circuits 24 and 25 each may comprise a conv0n-lO tlonal R-S flip-~lop circuit~ The reset input R o~ flip-~lop circuit 24 is connected to counter 21 for receiving outpu~ pulse CA therefrom, a~d ~.he set Input S of this flip-flop circuit is connected to the output of s~chroni3ing separator circuit 5 to receive the separated vertical synchronizing signal VD. Flip-flop circuit 25 has .~ts reset input R connected to the output ofcounter 23 to receive the output pulse CC therefrom, an~ its set input S ~onnected to t~e output of counter 22 to receive the output pulse CB. The Q ou~put of flip-flop circuit 25 is con-nected in common to respective inputs of AND gates 25 and 27.
~0 The other input of AND gate 26 is connected to the Q output: of flip-flop circuit 24, and the other input of AND gate 27 is con-n~cted to the Q output of fl;p flop circuit 24. As will be explained, flip-flop circuit 25 is adapted to generate the desired window pulse WX, ~Jhich is provided at t~e Q output 25 ~he~eof, and ~he complementaxy window pulse r~x is o~iained at its Q ou~put. ~ND gates 25 and 27 arP adapted to generate addi-tional wi~dow pulses, referred to herein as a delayed window pulse WY and an advanced window pulse WZ, respectivelyO Tha delayed window pulse is produced for a time duration following ~hP desired windGw pulse WX, and thus is dasisnated the delayed , window pulse; and the advanced window pulse is produced for a time duration preceding the desired window pulse, ~nd thus is desi~nated the ad~anced window pulse. The desired window pul~e ~X and its complement WX, toge~her with delayed window pulse ~Y
and advanced window pulse WZ are supplied to window de~ector 30.
~indow detector 30 is adapted to detect when the posi-; tion pulse PG generated by position ~ulse generator 3 occurs within the desired window pulse. Indica~ions are provided when this position pulse occurs during ~he dura~ion of the delayed window pulse and also during the duration of the advanced window pulse. The window detector is comprised of bistate c~rcuits 31, 32 and 33, each of which is illustra~ed herein as bein~ a timin~
pulse controlled flip-flop circuit~ such as a D-type flip-10p ; . circuit. Flip-flop circuit 31 se~ses when the position pulse occurs duri~g the adv~nced window pulse; and ~lip-10p circuit 33 senses when the position pulse occurs within the delay d window pulse WY. Flip-flop circuit 31 has its data input D connected to AND gate 27 to receive the advanced window pulse W~ ~hererom, ~nd its clock input CK connected via a delay circuit 14 to the output of pulse generator 3 to receive the position pulse PG.
Flip-flop circ~it 31 addit~onally includes a reset input R con-nected to the Q output o~ flip-flop circuit 25 to receive the com~lement of the desired window pulse WX. The Q output of flip-flop circuit 31 is connected to ~ control input of variable ~requency divider 10 to sup~ly the ratio control pulse DS thereto.
Flip-flop circuit 32 has its data inpu~ D connected to AND gate 26 to recei~e the delayed window pulse ~Y therefrom~
The clock input CX of this flip-~lop circuit is connected to receive the position puls2 PG su~plied from position pulse ~27;~315 ~enerator 3 via delay circuit l.4. The Q outpu~ oE 1ip-flop circuit 32 is connected to the data input D of flip~lop circUit 33, this flip-~lop circuit ha~in~ its clock input CK connected to the Q output of flip-flop circuit 25 to receive the desired window pulse WX therefrom, The reset input of 1ip-flop circuit 33 is connected to receive the position pulse PG supplied from position pulse generator 3 through dela,r cixcuit 14. The Q out-put of flip-flop circu;t 33 ;s connec~ed to the other control input o controllable frequency divider 10 to supply the ratio control pulse DU thereto. Delay circuit 14 imparts a constant time delay to the generated position pulse such that, when motor 1 is driven in synchronism with the horizontal and vertical synchro-nizing signals, the delayed position pu1s8 occurs in coincidence with the vertical synchronizing signal VD. Delay circuit 14 thus : 15 is provided to compensate for the particular positioning of the magnetic element~ included in position pulse generator 3, on the : motor drive shaft.
The manner in which th~ servo control apparatus illustrated in FIG. l operates now will be ~escxibed with refer-ence to the waveformc shown in FIGS~ 4A-4M. FI~,. 4A repre!;ents the vertical synchroniz~ng signal VD which is se.arated .~rom the video signal supplied to input ~erminal 4; and FIG. 4B represents the separated horizontal synchronizing signal. I~ îs ass~med that the vertical synchronizing s~gnal~ de~ine video f;eld intexvals, and that 262.5 line intervalsj- or horizontal synchronizing signals, are included in each field interval. It is further assumed that the frequency of the higher fre~uency re~erence pulses VN generated by VCO 7 is four times the horizontal synchronizing frequency.
Thus, during on6 field interval, that is, during the interval between two successive vertical synchroniziR~ si~nals VD; VCO 7 . --~12,7~j generates 1,050 synchronized higher frequency reEerence pulses Y~, as shown in FIG. 4C. Servo loop 11 synchronizes ~he operatlon o~
motor 1 with the frequency-divided re~erence pulses C~ produced by variable requency divider 10. It is recall~a that the frequency of signal FG, generated by ~requ~ncy generator 2, i5 equal to the fxequency of the frequency-divided reference pulses CM which are obtained at the output o~ divider 10~ If the divid-ing ratio o divider 10 is represented as M, and i the frequency of the higher frequency reference pulses UN is represented as NfH~
then the frequency of the position-representing signal FG should be equal to -~H~ wherein fH is the horizontal synchronizing frequency. Let it be assumed that motor 1 rota~es at ~e rotary speed of fO. Let it be furt~er assumed that the num~er of ma~netic teeth, or elements~ included in fre~u~ncy genera-~or 2, is repre-s~nted as G. ~ence, the frequency of the po~ition-representing signal FG may be represented as Gf~. S~rvQ loop 11 controls motor 1 such that the speed of t~is motor corresponds to the frequency -fH of the frequency-divided reerence PUlSeS CMo ~hus, Gf~=N~
Typical values for ~he NTSC sys~em are G=75, N=4, and M=14. In accordance with these numer~cal assumptions, the xo~ary speed fO
of motor 1 is equal to ~Q Hz, which is e~ual to th~ ield repetition rate. Of course, and a~ may ~e apprecia~ed, one or more o~ the factors G, N and M may ~e varied in the event that the rotarY
speed of motor 1 is, ~or example, 30 Hz, or any other rotary frequency. In the assumed example wherein the rotary speed of motor 1 is 60 Hz, this motor, tcgether with the magnetic head drive thereby, undergoes one rotation during each field interval.
As mentioned previously~ if there are x higher frequenc~
pul~es ~N generated during each ield interval, counter 21 countC
each such pulse until the count of x~2 is obtained. In the present ~7~S

example, it is. assumed that x=l,q5q. ~lence, aftex being reset by vertical sync~ronizing sLg~al VD, counter 21 counts 1,050/2, or 525 higher frequency pulses VN. When the coun~ o~ 525 is reached, counter 21 generates output pulse CA, as shown in FIG. 4D.
This output pulse CA occur~ su~stan~ially midway between two adja-cent vertical synchronizing signals VD, and i5 generated at the vertical synchronizing frequency. Flip-~lop circuit 24 is set in response to the separated vertical synchronizing si~nal VD, and is reset in response to the output pulse C~ to produce the pulse waveform RA at the Q output t~ercof, and the complementary pulse waveform RA a~ the Q thereof, as shown in FIG5. 4E and 4F, respectively.
After being reset by vertical synchronizing signal VD, counter 22 counts 1,043 higher frequency reference pulses VN.
Thus, and as shown in FI~ 4G, counter 22 produces the output pulse CB that leads the separated ~ertical sync~ronizins signal VD
by an interval equal to seven higher frequency refPrence pulses VN.
Counter 23, after being rese~ bv vertical synchronizing signal VD~
produces the output pulse CC after counting seven hLgher fre~usncy 2~ re~erence pulses V~. As shown i~ FI~ 4H, pulse CC lags v~rtical sy~chronizing signal V~ By an interval equal to seven higher ~re-quency reference pulses VN. Flip-flop circuit 25 i5 set in response to pulse C~, and reset in response to pulse CC. Thus, the Q output of flip-flop circuit 25 generates the des~red window pulse WX, as shown in FIG. 4I. It is seen that this desired window pulse is su~stan~ially centered with respe~t to the vertical synchronizing signal ~D. The complement WX of t~e desire~ window pulse is produced at the Q output of flip-~lop circui~ 25, as shown in FIG. 4~.

2~315 AND gate 26 produces the delayed windo~ pulse WY when the pulse waveform RA provided at the Q output o~ ~lip ~lop circuit 24 coincides with the complementary desired wind~w pulse WX, as shown in FIG. 4K. ~imilarly, AND yate 27 produces the advanced window pulse WZ when the pulse wave~orm RA (F~G. 4F) coincides w;th the complementary dssired window pulse WX,as shown in FI~. 4L.
When the phase, or position, of motor 1 is synchronized with vertical synchronizLng s;gnal VD, position pulse PG, obtained at t~e ou~p~t of delay circuit 14, occurs within the dur~tion of the desired windo~ pulse WX and, prefera~ly, coincides wi~h the.
separated vertical synchroni~ing signal VD, as shown in FIG. 4M.
The manner in which the spsed control servo loop 11 is further controlled to sync~roniæe the phase of motor 1 no~ will bP described ~ith reference to FIGS. 5A-5I. The vertical synchro-nizing signal VD, desired window pul~e WX, complementary desired window pulse WX, delayed ~indow-pulse ~, advanced window pulse WZ and position pulse PG, discussed previously with respsct to the wavefoxms shown in FIG~ 4, are represented in FI5S. SA-5F, respecti~ely. Let it ~a`assumed, initially, that the posi~ion pulse PG occurs in advance of, i.e., prior tot desired window pulse WX. This is represented as position pulse a i~ FIG~ 5F.
This means tha~ the magnetic head driven by motor 1 rotates into its predetermined positic~ at a time that is too early ~ith respect to vertical synchronizing ~ign~l VD.
A comparison between FIGS. 5E and 5F indicates t~at the ad~anced position pulse PG occurs during the dux~tion of ad~anced window pulse ~Z. The position pulse thus triggers flip-flop circuit 31 to the state correspondîng to ~hàt o~ the advancad window pulse. ~e~ce, t~e ~ outpu~ o flip-flop circuit 31 ls 1~.2~7~9Cj ~ provided with a binary "1", as shown in FIG. 5G. At the same : time, flip~flop circuit 3Z is triggered by posi~ion puls~ P~
: to the state determined by delayed window pulse WY. Since ~he delayed window pulse now is at its binary "0" level, 1ip-~lop circuit 32 remains reset.
Upon the occurrence o~ the positive transition in the complementary desired ~indow pulse WX, flip-10p circuit 31 is reset. Thus, and as shown in FIG. 5G, t~e ratio control pulse DS
is produced ~y ~lip-flop circuit 31 and supplied to varia~le frequency divider lO. This pulse has a duration from the time.
of occurrence of position pulse PG to the termination of desired window pulse WX. ~he purpos~ of this ratio control pulse DS is to increas~ the dividing ratio of frequency divider lO~ Thus, the higher frequency reference puls s V~ now are div~ded by the iS factor l/(M+1). In the foregoing example, it is assumed that Mal4.
Hence, varia~le frequency di~ider lO now i5 controlled to divide the frequenoy of the higher requency reference pulses VN by the factor 1/15. This reduces the fre~uency of f-equency-divided re~erence pulses CM. Servo loop 11 t~us drives motor 1 in accordance with this reduced fr~quency, so as to reduce th~.3 speed of the motor. This, in turn, delays t~e occ~rrence o~ pos:i~tion pulse PG relati~e to the time of occurrence of vertical synchroni2-ing siynal VD. That is, and w~len viewed in FIG. 5F, position pul~e a is shifted to the right ~ecause of the reduction in speed of Z5 motor l.
Position pulse b, as shown in FIG. 5~, is se2n to occur at a time t~at is closer t~ vertical synchronizing signal VD than before. Nevertheless, this pos;tion pulse occurs during the duration of advanced window pulse Wz. Hence~ as ~sfore, flip-flop circui~ 31 is set to ~he s~a~e determined by ~his advanced ~Z,7~2~35 .

window pulse and in respo~se to the posi-tion pulse PG so as to supply the ratio control pulse DS (~IG. 5G) to varia~le ~equ~ncy divider 10. Once again, the frequency o~ higher ~requency r0er-ence pulses VN is divided ~y ~he ~actor 1/15 for the durakion o the ratio control pulse DS. Th.~s, in turn, drive~ motor .L at a slower speed during this inter~al~ Consequently, t~e ~ime of occurrence of the position pulse is delayed; and, ultimately, i5 delayed to ~he point that ik occurs within the dura~ion of de~ired wLndow pulse WX. At that time, the phase o~ motor 1, that is, the position of the rotary ~agnet~c head driven t~ere~y, is within its desirea range.
The manner in which w-indow detector 30 operates to adjust the dividin~ ratio of varia~le fx~uency di~ider lQ so as to modify t~e operation of motor 1 whereby.the proper phase of lS that motor is attaine~ has been described with reference to the phase-leading occurrence of position pulse PG relativQ to desired window pulse WX. The manner in -wh;ch motor 1 is controlled in the event th~t the position pulse occurs in ~ phasa lagging rela-tionship with respect to the desired w~ndow pulse now will be 20 described with reerence to FIG5. 5R and 5I. Let it be assumed that position pulse c, s~own in FIG. 5F, oocurs during t~e duratio~
o delayed window pulse WY-. Flip-flop circuit 32 is set to the state of the delayed window pulse WY in response to this p~sition pulse. Henoe, the flip-flop circuit is set to produce the output 25 signal DT, shown ;n FIG. 5H, a~ its ~ outpu~. This signal DT is supplied to the D inpu o flip flop eircuit 33, whic~ i5 responsive ; to the commence~ent o~ the desired window pulse WX so as to ~e set to the state determined ~y sIgnal DT. As shown ~Il FIGu SI, flip-flop circuit 33 produc2s ths ratio control pulse DU at its 3Q Q output, and this pulse is supplied to the control inpu~ o ~17-~Z7~

~ariable fre~uency divlder 10. As mentioned abov~, ~atio control pulse DU sets the dividing ratio o~ thP ~reqUency divider to ~he factor l/(M-l), or l/13. ~Ience, the frequenc~f of the frequency-di~ided reference pulses CM is increased.
This, in turn, is used to drive motor 1 a~ an increased speed.
As ~he speed of the motor is increased, the time of occurrence of the position pulses PG is advanced relative to the desired window pulse WX. That is, and as viewed in FIG. 5F, t~e position pulses d, e, and so on, are shifted to the left.
Flip-flop circuit 33 is reset in response to the posi.~ion pulse PG which next occurs during the delayed window pulse WY, this position pulse being identified as position pulse d in FIG~ 5F. Hence, ratio con~rol pulse DU terminates in re--sponse to po~ition pulse d, as shown in FIG. 5I.
The occurrence of the next position pulse e also is assumed to be delayed relative to the desired ~indo~ pulse ~
Hence, flip-flop circuit 33 once again is set in response to the commencement of the desired ~indow pulse, and inasmuch as flip-flop circuit 32 had remained in its set state to cont.inue the application of signal DT ~o flip-flop 33. Con~equently, ratio control pulse DU once again is supplied to vaxiable :Ere-quency divider 10, this pulse being terminated in rssponse to the occurrenc of position pulse e. That is, the duration of ratio contxol pulse DU extends from the commencement of 'he desired window pulse WX to the.occurrence of the.next-following po~ition pulse PG. Once again, ratio con~rol pulse DU reduces the frequency-dividing ratia of divider 10 so as to increase the requencv of frequen~y-divided reerence pulses C~ his, in turn, increases the speed of motor 1 so as to advance the tim~
of occurrence of the position pulse.

~Z~ 5 Ultimately, posikion pulse P~ will be shifted so a~
to ocour within ~he duration of desired windo~ pulse W%. At that time, the occurrence Q~ the posi~ion pulse PG, as applled to the clock input CK o~ flip-flop circuit 32, will coincide with the binary "0" level of delayed windo~ pulse ~Y. This means that flip-flop circuit 32 will be reset so as to terminate signal DT, as shown in FIG~ 5H. Ne~ertheless, and as shown in ~IG. 5I, the ratio control pulse DU, al~eit very narro~, will ha~e ~een generated from the comm~ncement of the desired window pulse WX until the occurrence o the position pulse PG.
It is appreciated that the normal diviain~ ra~on o frequency aiv;der 10 is equal to 1/14. This normal dividin~
ratio is increased to th.e ~actor 1~15 only during the interval of each ratio control pulse DS, and i5 reduced to the factor 1/13 only during the inter~al of each ratio control pulse DU. During those times ou~side these intervals, the dividing ratio o vari-able requency divider 10 returns to its normal factor of 1/14.
~ence, the frequency of t~e fre~uency-divided refe~e~e pulses CM is seen to ~e reduced or ~ncreased only dur~ng those.brief 20 intervals wh~ch coincide ~t~ ~e durations of ratio pulse DS
and DU~ Never~eIess, such ~rief modulation~ in the ~requency of fre~uency-di~ided reference pulses ~.~ are suffIcient to adjust th~ operation of motor 1 such t~at t~e phase t~.ereof ~ecomes e~ual to a desired phase. That ;`5, t~ess adjustments to the operation Q~ motor 1 are successful in s~ifting position ~ulse PG so as to occur within the duration ~f th~ desired win~o~ pulse ~X.
.: -Xt should be appreciated that, since the. frequenc~ of fr~quency-di~ided xeference pulses CM is eq~al ~o t~ fraquency of speed-representing si~gnal ~G, the~paxiod of pul~es CM is equal to ~he p~riod of speed-repres~lting signal FG, i.e , t~.e ~itch of ~1%~ 35 the magnetic teeth of frequenc~ aenerator 2. The period o ~reauency-divided re~erence pulses C~l IS equal ~o one-ou~kee~th the period of higher frequency reerence pulses ~N. That is, fourteen reference pulses VN can be contai.ned ~i~hin the period of ~requency-divided reference CM~ It is xecalled that the dura-tion of desired ~indow pulse ~ is equal to ourteen higher fre-quency reference puls~s VN. Thus, the duration o~ desired,pulse WX is equal to th~ period of requency-d;vided reference pulses C~l which, in turn, is equal to the pitc~ of th~ magnetic teeth of frequency generator 2.
It is further appreciated that the'duration of ratio control pulses DS and DU is directly related to ~he phase differ-ence between position pulse PG and desired window pulse ~ As this phase error is reduc~d, the duration of the respectiYe rario control pulse likewise is red'uced~ FIG. 3 i5 a graphical represen-tation of the phase difference between positio~ pul~a PG and d~sired windQw pulse T~X ~ and ~h~ phase error volta~e pro~uced b~
phase comparator 1~ More particularly, curve 51 i~ a negative voltage p~oduced ~ comparator 12 to reduce the speed cf motor 1 2Q when position pulse PG is ~n a pha,se-leadin~ relation with respect to desired ~r.dow pulse WX~ Conversely, curve 52 i5 a pos:itiye ~oltage produced ~y comparat~r 12 to ;ncrease th speed of motor 1 w~en pos~tion pulse. PG ~s in a phase-lagging reIat~on with re~pe~t to the'des:irea w~ndo~ pulse~' It is s~e~ that t~e. erro~
~oltage 's reauced to zero ~h.e~ t~e posit~-on pu1se PG occurs within th~ durat~on o~ t~e.desired window pulse l*~.
FrQm the foregQ~ng description of t~e operation o~
FIG~ 1, t l`s seen tha,t. ~he'ser~Q control apparatus illustrated ~erein is e~fec'tive to control motor 1 suc~ t~at i~s phase, or pos;:tio~, occur~ with~n a desired range. When t~is apparatus i5 ~20-.

used in a V~R, t~e magne~ic h~ad is controlled so as to ~e within a d~sired range of, ~or example, ~hs.beginning o~ ~ ~ecord tracX, at the time of occurr0nce of the.video synchroni~ing signal. As will now be described, another aspect o~ this ir.vention is to pro~ide accurate control over m~tor 1 such that its phase corre-sponds precisely to a desired phase. Referring to FIGS. 6A-6F, the particular rela~ionship of t~e various signals used in the servo control apparatus, and discussed in de~ail above, is recrea~2d.
As mentioned previouslyt.the desire~ window pulse WX, sho~m in FIG. 6B, is gen~rated so as to be su~s~antially centered on the separated vertical sync~roni-zing signal VD, shown in FIG. 6A.
Furthermore, the duxa~ion of t~e desired window pulse WX, is sufficient to conta~n ~ourteen higfier frequency reference pulses VN,.as show~ in FIG. ~C. Eac~ of these fourteen hi~her frequency reference puls~s is numbered, for convenience. St~ll further, since the frequency o~ the freguency~divided reference puises C~
is equal to the ~re~uency of the speed-representing pulsas FG at the time that the phase of motor 1 is ~ithin its desired ran~e., t~ese pulses C~ and signal FG are synchronized, as shown in FIGS~ 6D and 6E. That ist servo. loop 11 opexates such that frequercy-aivided reference pulses C~ coincide ~ith speed-representing si~nals FG.
: The magnet~c. element which is încluded in position pulse generator 3 15 located suc~~that position pulse P~, s~lch as a~
the output of delay circuit 14, occurs within a prsdet2rmined tl~.e follo~ing the occurren.ce o.~ a speed-representin~ pulse s.isnal FG. For the purpos~ ofi the pr~sen-~ dîsucssion t this time i~terval between the o-currenc~ o~ tfie speed-representing pulse siqn~l and th~ posi.tion puls~ corresponds to ~ 5 ~.ig~er fr~quenc~ ref æ enee pulses VN~ Thîs r~latîons~ip i5 s~o~n in FIG. 6F~ T~us, mot¢r 1 -~7;;~5~"5 may be controlled such that when both a frequency-divided pulse CM and a speed-representing pulse signal P~ occur at, for example, the third reference pulse VN included in the desired windo~ pulse WX, position pulse P~, will occur between the eleventh and twelth reference pulse. Since vertical synchronizing signal VD occurs at the eighth reference pulse VN, it is seen that, în the example assumed herein, posi~ion pulse PG is phase displaced from the ver-tical synchronizing si~nal by 3.5 reference pulses. If the phase of motor 1 ca~ ~e adjusted such that the frequency-divided refer-ence pulses CM and coinciding sp~ed~representing pulse signals FGoccur at the location represented ~y the broken lines in FIGSo 6D
and 6~, that is, a~ the fourteenth highex frequency reference pulse VN, then posi~ion pulse PG, which is phase delayed from the speed represen~ing pulse siynal by 8.5 reerence pulses VN~ will occur between the eighth and ninth re~erence pulse. This is sub-stantially phase coincident with the vertical s~nchronizing signal VD .
The foregoin~ control over the phase of motor l such that position pulse PG is adjusted to coincide with vertical synchronizing signal vn i5 ~arried out by the embodiment ~ho~n in FIG~ 2. The servo control appa-atus shown in FIG. 2 is sub-stantially similar to that discussed previously with respect to FIG. 1, and like referenGe numerals are used to identify the same elements. he em~odiment of FTG. ~ also irLcludes a phase 25 modula~ing circuit for modulating the phase of the ~requency-divided reerence pulses CM produced by variable ~requency divider 10~ This phase modulating circuit is comprised of a counter 41, a latch circuit 42 and a decoder 43. Counter 41 i5 coupled to phase locked loop 6 to receive the higher requencY

30 reXerence pulses VN genera~ed by VCO 7. This counter is adapted 7~

to count cyclically to four-~een, the count being increme~-~ed ln response to each of the higher re~uency rsference pulses VN.
In addi~ion, counter 41 includes a reset ~exminal connected to synchronizing signal separator 5 to receive the separated vPrtical s~nchronizing signal VD. Thîs vertical sy~c~roni~ing signal is adapted to preset t~e count of counter 41 to a predetermined count, such as a count of eight. This synchxonizes the operation of counter 41 with the operat~on of window pulse generator 20 (FIG. 1) and insurPs that t~e count of this counter will be at the preset count thereo~ upon the occurrence of the vertical synchronizins signal.
Counter 41 may comprise a conventional digital _ounting circuit adap~ed to produce a 4-bit count, this count ~eing supplied, in parallel, to latch circuit 42. The latch circuit includes con-trol inputs connected to windo~ pulse generator 20 and to delavcircuit 14, respectively. These control inputs receive the ; desired window pulse ~ from windo~ pulse generator 20 and the position pulse P~ fxom delay circuit 14. La~ch c-rcuit 42 i~
adapted to "latch" or store, the count suppLied thæreto by count~r 41 in response to the occurrence of t~e desired window pulge r~x and the position pulse PG. The latch cir~uit t~u~ may include conventional storage elem~nts having inpu~ gates wh~ch are energi~ed, or opened~ w~en the posltion pulse PG occurs within the duration of the de~ired w-indow pulse WX. ~rhe output o~ latch circuit 42 is coupled to decoder ~3. The decoder may comprise conventional lo~ic c~rcuitry adapted to perform thc math~matical func.ion 14 ~ (8 - N)~ w~erein ~ is the count stored in latch ci~cuit ~2. This ~ecoded function i5 supplied by decoder 43 to another control input o~ variable requency d~id~r 10 50 as to varv the fre~uency dividing ratio o~ th latter. For example, 1~27;~:~35 i~ decoder 43 produces ~ decoded outpu~ corr~sponding to the.
digital count of 11, t~e dividing ra~io o~ variable requency divider 10 is changed from its normal d;vidin~ ra~io 1/14 to the dividing ra~io 1/1~. Similarly, i decoder 43 produces a decoded output corresponding to the digi~al count of, for exa~..ple, 17, the dividing ration of fr~uency divider 10 is changed from its normal ratio 1/14 to the decod~d ratio 1/17.
Latch circuit 42 and decoder 4~ are adapted to be reset, or cleared, in response to the termination of the desired window pulse WX.
The manner in whic~ t~e em~odiment shown in FIG~ 2 operates no~ will be des~rihed wit~ reference to FIG.S.7A-7D2.
It is appreciated that ~he illus~rated servo con~rol apparatus operates in the manner descri~ed pre~iously with respect to FIG. 1 in order to control motor 1 s~ch khat posi~ion pulse PG occurs within ~he dura~ion of the desired window pulse WX. It is re-called that this represents ~hat ~he phase of motor 1 is ~ithin a desired range. The phase o thi.s motor is controlled ~y the illustra~ed phase modulating circult so as to correspond to a precise, desired phase. Tn~ vertical synchronizing signal VD, de~ired ~indow pulse WX and hig~er ~re~uency refer~nce pulses ~JN r discussed in detail abov~, are presented aga~n in FIGS. 7A, 7B and 7C, respectively. ~et it ~e assumed that the.position pulse PG
occurs during the latter half portion ~ the desired window pulse WX, as re~resented by ~he position puls~s PG of ~IG. 7Dl. Coun~er 41 counts t~e h~gher frequency reference puls.~s V~ generated b~
~CO 7. This counter counts from 1 to 14, and then is recycled.
: This opera~ion o~ the co~ter is synchronized with tk gene~ation o~ desired window pul~e WX ~y r~setting the coun~ Q~ cour.ter 41 to a count of 8 in response ~o eac~ vex~ical synchronizing signal VD

~z~

~ hen position pulse PG occurs within the duration o desired window pulse ~X, the count then reached by count~r 41 is latched in latch circuit 42. In the example described ~lith.
respect to FIG. 7Dl, it is assumed that counter 41 has rea~hed S a count of ll at the time that position pulse P~ occurs. Hence, latch circuit 4Z latches this count of 11 therein. Decoder 43 performs the function of 14 ~ (8 - 11) = 11; and supplies this decoded signal as a ratio control pulse to frequency divider 10.
The dividing ratio of varia~le frequency divifler 10 thus is changed .or one dividing cycle thereof from a dividing ratio of : lJl4 to a dividing ratio of 1/ll. The resultant brie change ~n tha frequency of fre~uency-divided rersrence pulses CM resul~s in a phase shif~ of these pulses, as shown in FIG. 7Dl. Servo loop 11 now drives motor l such that ~peed-representing plllse 15 signals FG tend to co~ncide with the phase-shifted frequency-divided reference pulses C~. Of course, a~ the spee~-representing pulse signal is phase adjusted, the position pulse PG, which occurs at a time delayed by~ 8.5 reference pulses V~ ~rom pulse signal FG, likewise is phase adjusted. It is seen that, ini-~0 tially, position pulse PG occurs between the eleventh and t.welfthhigher frequency reference pulses VN. This corresponds wit:h the occurrence of fre~uency-divided reference pulse CM and speed-representing pulse signal FG at t~e third higher frequency refer-ence pulse. Decoder 43 operatPs variable fre~uency divlder lO so as to, effectively, shift the time of occurrence of the re~uency~
divided reference pulses CM to occur at the ourteenth hig~r fre-quency reference pulse VN. Servo loop ll driv~s motor 1 such t~a~
speed-represen~in~ pulse signals FG likewise occur at the lour-teenth higher frequenov re~erence pulse, as shown at t~e right-hand portion of FXG. 7D~ he~ ihe speed-~ep~esentiny pulse -2~

~P~ 95 signal FG occurs at the fourteenth higher frequency reference ; pulse, position pulse PG, ~ich.is delayed bv 8.5 hi~hex requency re~erence pulses, occurs between the eighth and ninth re~e~nce pulse VN. This is in su~stantial phase coincidence with ~e.r~ical synchroniæing signal V~. Hence, the phase modulating c~rcuit.
adjusts the phase o ~requency-di~ded reference pul.ses C~ so as to drive motor 1 to its precise, desired phase.
Now, let it be assumed that position pulse PG occurs during the ~irst half portion of desired windo~ pulse WX, as shown in FIG. 7D2. It ~ assumed herein that position pulse PG
occurs ~etween the fifth and sîxth higher requency reerence pulses VN. Since position ~ulse PG ~s delayed from s.peed-representing pulse signal FG ~y 8.5 of these h}gher frequency reference pulses VN, it is seen that the speed-representing pulse signal, which is ~ynchronized ~ith the frequency-divided pulses CM, occurs i~ coincidence ~ith the ele~enth high~r re-quency reference pulse VN.
As before, counter 41 counts the higher frequency re~rence pulses VN supplied t~ereto ~y ~CO 7. At ~he time of occurrence of the positi.~n puls~ P& (within, o~ course, the durat;on of the desired` ~ndo~ pulse ~X), latch c rcu~t 42 latches the count reached ~ co~ter 41. It is appreciateJd t~at latch circuit 42 no~ latc~es a count of 5. DecQder 43 per~orms th0 math~matical func~ n of 14 ~ (8 - 5) so as to ~upply the decoded count of 17 ~o ~aria~le frequenc~ d~v~der 10.
This decoded count functions as a ratio control pul~e to c~ange.
the frequency-dividing rat~o of frequency divider 10 frQm ~ts normal xatio of 1~14 to ~he ratio 1/17~ as dete~mlned ~y decoder 43. ~is c~ange in the ~re~uency di~idin~ ratio ~s carried out for only one cycle of varia~le frequency divider 10.

.~
:`
-2~-~ 272~5 From FIG. 7D2, it i5 seen that this c~ange in the dividing ratio of frequency div~der 10 delays the occurr~nce of the next frequency-divided reference pulse CM ~om its normal tLme o occurrence at the ele~enth hi~her ~requency re~erence pulse VN to the neT~ tLme of occurrence o~ the our-teenth higher fre~uency reference pulse. As before, servo loop : 11 drives motor 1 in response to these phase-shift2d frequency-divided reference pul~es C~ such that the phase of motor 1 is varied until t~e speed-representing pulse signals FG coincide with the frequency-divided reference pulses C~, a~ s~own at the right-hand portion o FIG. 7D2. When speed-representing reer-ence pulses FG occur at ~e fourteenth higher frequency reference ~ulse VN, the position pulse PG, which is displaced from the speed-representing pulse signal ~y 8.5 of the higher frequency reference pulses, now occurs between the eighth and ninth higher frequency reference pulses. This is in substantîal coincider.ce with ~he vertical synchronizi~ signal VD.
Thus, it is seen that the em~odiment illustrated in FIG. 2 serves to adjust t~e p~ase of motor 1, and more spec~f~cally, the member which i5` driv~n by mot~r 1, suc~ t~at the ~hase, or position, of that mem~er ~5 in precise synchronism wit~ th~
vertical synchronizing sis~al ~D~
While t~e present in~e~tion has ~een particularly shown and descri~ed ~it~ refere~ce to certain pre~erred embodi~
men~s, it should ~e rea~ily apparent to those o~ ordinary skill in the art that various changes and modifications ln form and details can ~e ir.adP w~ithout d~par-~ng ~rom the spirit and scope of t~e invention. For example, the sexvo control appar~tus dis-closed herein can be used in a VTR, ~or example/ ~o cc:ntrol 30 either t~e rotation of ~he magn~ic head or, alternatively, the .

9~5 mo~ement of the magnetic tape~ In t~e latter environment, motor 1 i5 used to dri~e the caps~an which, în kurn, dri~es the tape. Position pulse PG will, in ~ha~ en~ironment, be reproduced from the usual control pulse track tha~ is recorded on such a tape. The servo control apparatus nevertheless will control motor 1 such that the tape driven thereby is at its proper phase, or position, at the time of occurrence of the ~ertical synchronizing signal. Indeed, the present invention need not ~e limited soleIy to video si~nal recording or repro-ducing applications. Th~ present invention can ~e used readilyto control the phase o ot~er driven members. I~ is, ~herefore, intended that ~he appended cla~ms ~e interpre~ed as includin~
all such changes and modifications.

Claims (28)

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

1. Servo control apparatus for controlling a driven member comprising:
a source of reference signals having a frequency determinative of the speed at which said member is driven;
means for deriving signals representing the actual speed at which said member is driven;
a servo loop responsive to said reference signals and to the speed representing signals for driving said member at a speed determined by the frequency of said reference signals;
means for deriving signals representing the actual position of said driven member;
window pulse generating means for generating window pulses corresponding to desired positions of said driven member;
means for detecting when the position representing signals occur within the duration of said window pulses;
modulating means for modulating the frequency of said reference signals if said position representing signals occur outside said duration of said window pulses, to adjust the speed and position of said driven member until said member is driven such that the actual positions thereof correspond to said desired positions; and phase modulating means for modulating said reference signals to adjust the position of said driven member such that said position pulse occurs at a predetermined location within said window pulse.

2. In a video signal recording/reproducing system, servo control apparatus for controlling the speed and phase of a driven member in synchronism with the horizontal and vertical sychronizing signals, respectively, of a video signal, (Claim 2 con't.) comprising controllable oscillator means for generating relatively higher frequency pulses synchronized with said horizontal synchronizing signal;
controllable frequency divider means coupled to said controll-able oscillator means for dividing the frequency of said higher frequency pulse;
means for deriving speed representing signals having a frequency representing the actual speed of said driven member;
speed control means, including phase comparator means for comparing the phase of the frequency-divided pulses produced by said frequency divider means to the phase of said speed re-presenting signals, to control the speed of said driven member such that said frequency-divided pulses and said speed re-presenting signals are in phase synchronism;
means for producing a position pulse when said member is driven to a predetermined position, such that said position pulse re-presents the actual position of said member;
window pulse generating means responsive to said vertical synchronizing signal to generate a desired window pulse, an advanced window pulse, and a delayed window pulse, including means for determining the approximate mid-point between adja-cent vertical synchronizing signals and to generate said desired window pulse substantially centered on a vertical synchronizing signal, said advanced window pulse extending from said determined mid-point to said desired window pulse, and said delayed window pulse extending from said desired window pulse to said determined mid-point; and divider control means coupled to said window pulse generating means and responsive to said position pulse to sense whether said position pulse occurs within said desired window pulse and to increase or (Claim 2 Con't.) decrease the dividing ratio of said controllable frequency divider means if said position pulse occurs in advance of or delayed from said desired window pulse, respectively, whereby the speed of said driven member is reduced or increased, re-spectively, so as to correspondingly shift the phase of said driven member.

3. The servo control apparatus of claim 2 wherein said divider control means comprises increase control means for supplying an increase ratio pulse to said controllable frequency divider means having a duration extending from the occurrence of said position pulse to the termination of said desired window pulse, if said position pulse occurs during said advanced windowpulse, to increase said dividing ratio from a normal ratio by a constant, predetermined amount during the duration of said increase ratio pulse; and decrease control means for supplying a decrease ratio pulse to said controllable frequency divider means having a duration extending from the commencement of said desired window pulse to the occurrence of said position pulse, if said position pulse occurs during said delayed window pulse, to decrease said dividing ratio from said normal ratio by a constant, predetermined amount during the duration of said decrease ratio pulse.

4. Servo control apparatus for controlling a driven member, comprising a source of reference signals having a frequency determinative of the speed at which said member is driven;
means for deriving signals representing the actual speed at which said member is driven;
a servo loop responsive to said reference signals and to the speed representing signals for driving said member at a speed determined by the frequency of said reference signals;

(Claim 4 Can't.) means for deriving signals representing the actual position of said driven member;
window pulse generating means for generating window pulses corresponding to desired positions of said driven member, including advanced window generating means for generating a phase advanced window pulse, delayed window generating means for generating a phase delayed window pulse, and desired window generating means for generating a desired window pulse separating said phase advanced window pulse from said phase delayed window pulse;
means for detecting when said position representing signals occur within the duration of said phase advanced window pulse to produce a frequency reducing signal, when said position representing signals occur within the duration of said phase delayed window pulse to produce a frequency increasing signal, and when said position representing signals occur within the duration of said desired window pulse to produce a normal signal; and modulating means for modulating the frequency of said reference signals if said position representing signals occur outside said duration of said desired window pulses, to adjust the speed and position of said driven member until said member is driven such that the actual positions thereof corre-spond to said desired positions.

5. The apparatus of claim 4, wherein said modulating means includes means for supplying pulses at a substantially constant, higher frequency; and frequency divider means for normally dividing the frequency of said supplied pulses by one factor when said position representing signals occur within the duration of said desired window pulses and for dividing the frequency of said supplied pulses by a different factor when said position representing signals occur outside said duration of said desired window pulses, the divided pulses produced by said frequency divider means being used as said reference signals.

6. The apparatus of claim 5 wherein said frequency divider means is responsive to said normal signal to divide the frequency of said supplied pulses by a normal factor, whereby said reference signals have a normal frequency to cause said servo loop to drive said member at a normal speed; said fre-quency divider means is responsive to said frequency reducing signal to divide the frequency of said supplied pulses by a higher than normal factor, whereby said reference signals have a less than normal frequency to cause said servo loop to drive said member at a slower than normal speed so as to retard the occurrence of said position representing signals to within the duration of said desired window pulse; and said frequency divider means is responsive to said frequency increasing signal to divide the frequency of said supplied pulses by a lower than normal factor, whereby said reference signals have a greater than normal frequency to cause said servo loop to drive said member at a faster than normal speed so as to advance the occurrence of said position representing signals to within the duration of said desired window pulse.

7. In a video signal recording/reproducing system, servo control apparatus for controlling the speed and phase of a driven member in synchronism with the horizontal and vertical synchronizing signals, respectively, of a video signal, comprising:
controllable oscillator means for generating relatively higher frequency pulses synchronized with said horizontal synchronizing signal;
controllable frequency divider means coupled to said (Claim 7 Con't.) controllable oscillator means for dividing the frequency of said higher frequency pulses;
means for deriving speed representing signals having a frequency representing the actual speed of said driven member;
speed control means, including phase comparator means for comparing the phase of the frequency-divided pulses produced by said frequency divider means to the phase of said speed representing signals, to control the speed of said driven member such that said frequency-divided pulses and said speed representing signals are in phase synchronism;
means for producing a position pulse when said member is driven to a predetermined position, such that said position pulse represents the actual position of said member;
window pulse generating means responsive to said vertical synchronizing signal to generate a window pulse having a center portion that substantially coincides with said vertical synchronizing signal; and divider control means coupled to said window pulse generating means and responsive to said position pulse to sense whether said position pulse occurs within said window pulse and to increase or decrease the dividing ratio of said controllable frequency divider means if said position pulse occurs in advance of or delayed from said window pulse, respectively, whereby the speed of said driven member is reduced or increased, respectively, so as to correspondingly shift the phase of said driven member.

8. The servo control apparatus of claim 7 further comprising phase control means for controlling the phase of the frequency-divided pulses produced by said frequency divider means during said window pulse so as to adjust the phase of said position pulse.

9. The servo control apparatus of claim 8 wherein said phase control means comprises counting means for counting the higher frequency pulses generated by said controllable oscillator means during each said window pulse; detecting means for detecting the count of said counting means at the time of occurrence of said position pulse during each said window pulse;
and; and means for changing the dividing ratio of said con-trollable frequency divider means in accordance with said count, if said count differs from a predetermined count.

10. The servo control apparatus of claim 9 wherein said means for changing the dividing ratio is operative once during each window pulse.

11. Servo control apparatus for controlling a driven member, comprising:
a source of reference signals having a frequency determinative of the speed at which said member is driven;
means for deriving signals representing the actual speed at which said member is driven;
a servo loop responsive to said reference signals and to the speed representing signals for driving said member at a speed determined by the frequency of said reference signals;
means for deriving signals representing the actual position of said driven member;
window pulse generating means for generating window pulses corresponding to desired positions of said driven member;
means for detecting when the position representing signals occur within the duration of said window pulses; and modulating means for modulating the frequency of said reference signals if said position representing signals occur outside said duration of said window pulses, to adjust the speed and position of said driven member until said member is driven such that the actual positions thereof correspond to said desired positions.

12. The apparatus of claim 11 wherein said modulating means comprises means for supplying pulses at a substantially constant, higher frequency; and frequency divider means for normally dividing the frequency of said supplied pulses by one factor when said position representing signals occur within the duration of said window pulses and for dividing the frequency of said supplied pulses by a different factor when said position representing signals occur outside said duration of said window pulses, the divided pulses produced by said frequency divider means being used as said reference signals.

13. The apparatus of claim 12 wherein said speed representing signals are pulse signals having a frequency corresponding to the actual speed of said member; and wherein said servo loop comprises a phase comparator for comparing the phase of said speed representing pulse signals to the phase of the frequency divided pulse signals, and means for changing the speed at which said member is driven in accordance with the phase comparison.

14. The apparatus of claim 12 or 13 wherein said source of reference signals comprises a controllable oscillator for supplying said pulses at said higher frequency; means for pro-viding synchronizing pulses; and a phase-locked loop for synchronizing said controllable oscillator to said synchronizing pulses.

15. The apparatus of claim 11 wherein said driven member comprises a motor driven rotary transducer for recording and/
or reproducing video signals; and said means for deriving position representing signals comprises sensing means for sensing when said transducer rotates to a predetermined position and for generating a position pulse.

16. The apparatus of claim 11 wherein said driven member comprises a magnetic medium for recording and/or reproducing video signals, said magnetic medium having periodic control signals recorded thereon; and said means for deriving position representing signals comprises a sensing transducer for reproducing each control signal as a position pulse.

17. The apparatus of claim 15 or 16 wherein said source of reference signals comprises synchronizing separator means for separating the horizontal and vertical synchronizing signals included in said video signals.

18. The apparatus of claim 17 wherein said window pulse generating means comprises desired window generating means for generating a desired window pulse that is substantially centered with respect to a vertical synchronizing signal; advanced window generating means for generating an advanced window pulse commencing substantially midway between two successive vertical synchronizing signals and terminating at the commencement of said desired window pulse; and delayed window generating means for generating a delayed window pulse commencing at the termin-ation of said desired window pulse and terminating at the commencement of said advanced window pulse.

19. Servo control apparatus for controlling a driven member by which video signals are recorded and/or reproduced, comprising a source of reference signals having a frequency determinative of the speed at which said member is driven, said source including synchronizing signal separator means for separating the horizontal and vertical synchronizing signals included in said video signals;
means for deriving signals representing the actual speed at which said member is driven;

(Claim 19 Con't.) a servo loop responsive to said reference signals and to the speed representing signals for driving said member at a speed determined by the frequency of said reference signals;
sensor means for sensing when said member arrives at a pre-determined position and thereby providing position pulses representing the actual position of said driven member;
window pulse generating means for generating window pulses corresponding to desired positions of said driven member, including desired window generating means for generating a desired window pulse that is substantially centered with respect to a vertical synchronizing signal; advanced window generating means for generating an advanced window pulse commencing substantially midway between two successive vertical synchronizing signals and terminating at the commencement of said desired window pulse; and delayed window generating means for generating a delayed window pulse commencing at the termin-ation of said desired window pulse and terminating at the com-mencement of said advanced window pulse;
means for detecting when the position representing signals occur within the duration of said window pulses; and modulating means for modulating the frequency of said reference signals if said position pulses occur outside said duration of said desired window pulses, to adjust the speed and position of said driven member until said member is driven such that the actual positions thereof correspond to said desired positions, said modulating means including pulse generating means for gen-erating a train of pulses synchronized with said horizontal synchronizing signals and variable frequency divider means for dividing the frequency of said train of pulses by a predeter-mined factor when said position pulse occurs within said de-sired window pulse, for dividing the frequency of said train of pulses by a higher predetermined factor when said position pulse occurs within said advanced window pulse, and for dividing the frequency of said train of pulses by a lower pre-determined factor when said position pulse occurs within said delayed window pulse, the frequency-divided train of pulses being applied to said servo loop.

20. The apparatus of claim 19 wherein said desired window pulse generating means comprises bistate means; first counting means reset to an initial count by said vertical synchronizing signal for counting the pulses included in said generated train of pulses to produce a set signal when a first predetermined count is reached; and second counting means reset by said vertical synchronizing signal for counting the pulses included in said generated train of pulses to produce a reset signal when a second predetermined count is reached; said bistate means being set to a first state by said set signal and being reset to a second state by said reset signal.

21. The apparatus of claim 20 wherein said advanced window generating means comprises second bistate means;
additional counting means reset to an initial count by said vertical synchronizing signal for counting the pulses included in said generated train of pulses to produce a reset signal when a predetermined count is reached substantially midway be-tween successive vertical synchronizing signals, said second bi-state means being reset to a first state by the reset signal produced by said additional counting means and being set to a second state by said vertical synchronizing signal; and gate means for producing said advanced window pulse when said second bistate means is in its first state and the first-mentioned bistate means is in its second state.

22. The apparatus of claim 21 wherein said delayed window generating means comprises additional gate means for producing said delayed window pulse when said second bistate means is in its second state and said first-mentioned bistate means is in its second state.

23. The apparatus of claim 19 wherein said means for detecting comprises first divider control means for producing a first control pulse to cause said variable frequency divider means to divide the frequency of said train of pulses by said higher predetermined factor, said first control pulse commencing upon the occurrence of said position pulse within said advanced window pulse and terminating in response to the termination of said desired window pulse; and second divider control means for producing a second control pulse to cause said variable frequency divider means to divide the frequency of said train of pulses by said lower predetermined factor, said second control pulse commencing in response to the commencement of said desired window pulse if said position pulse has occurred within said delayed window pulse and terminating in response to the next occurrence of said position pulse.

24. The apparatus of claim 23 wherein said first divider control means comprises first bistate means being set to a first state during said advanced window pulse and in response to the occurrence of said position pulse, and being reset to a second state in response to the termination of said desired window pulse, said first control pulse being derived from said first state of said first bistate means.

25. The apparatus of claim 24 wherein said second divider control means comprises second bistate means being set to the same state as said delayed window pulse and in response to said position pulse; and third bistate means being set to a first state by a first state of said second bistate means and in response to the commencement of said desired window pulse, and being reset to a second state by said position pulse, said second control pulse being derived from said first state of said third bistate means.

26. The apparatus of claim 19 further comprising sensing means for sensing the relative location within said desired window pulse at which said position pulse occurs; and means for temporarily adjusting the factor by which said variable fre-quency divider means divides the frequency of said train of pulses as a function of said sensed relative location of said position pulse, whereby the driving of said member is temporarily adjusted to shift the occurrence of said position pulse to a predetermined location within said desired window pulse.

27. The apparatus of claim 26 wherein said sensing means comprises counting means for counting the number of pulses included in said train of pulses during the duration of said desired window pulse until the occurrence of said position pulse; and temporary storage means for storing the count ob-tained by said counting means.

28. The apparatus of claim 27 wherein said means for temporarily adjusting comprises decoding means for decoding the temporarily stored count and applying the decoded count to said variable frequency divider means, whereby the factor by which said variable frequency divider means divides the frequency of said train of pulses is changed in accordance with said decoded count so as to adjust the phase of said reference signals and, thus, the phase of said driven member.