CA1048146A - Speed and phase control system - Google Patents
Speed and phase control systemInfo
- Publication number
- CA1048146A CA1048146A CA210,385A CA210385A CA1048146A CA 1048146 A CA1048146 A CA 1048146A CA 210385 A CA210385 A CA 210385A CA 1048146 A CA1048146 A CA 1048146A
- Authority
- CA
- Canada
- Prior art keywords
- speed
- counting
- count
- phase
- signals
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02P—CONTROL OR REGULATION OF ELECTRIC MOTORS, ELECTRIC GENERATORS OR DYNAMO-ELECTRIC CONVERTERS; CONTROLLING TRANSFORMERS, REACTORS OR CHOKE COILS
- H02P29/00—Arrangements for regulating or controlling electric motors, appropriate for both AC and DC motors
- H02P29/0016—Control of angular speed of one shaft without controlling the prime mover
- H02P29/0022—Controlling a brake between the prime mover and the load
Landscapes
- Engineering & Computer Science (AREA)
- Power Engineering (AREA)
- Control Of Velocity Or Acceleration (AREA)
- Television Signal Processing For Recording (AREA)
- Adjustment Of The Magnetic Head Position Track Following On Tapes (AREA)
- Control Of Electric Motors In General (AREA)
- Indexing, Searching, Synchronizing, And The Amount Of Synchronization Travel Of Record Carriers (AREA)
Abstract
SPEED AND PHASE CONTROL SYSTEM
ABSTRACT OF THE DISCLOSURE
In video reproducing apparatus having a rotating head, a pulse generator produces pulses synchronously with the rotation of the head. A counter begins counting clock signals at the time of each of the pulses and continues counting until the next pulse. The final count at the end of each counting cycle is converted to an analog signal to control the speed of ro-tation of the head. The phase angle of the head is controlled by control pulses recorded on the tape, which are compared with pulses from the pulse generator to affect incrementally the same speed control mechanism. The starting count of each counting cycle is varied in accordance with the time between successive control signals so that the final count will be the same as long as rotation of the head is synchronous with the control signals. This allows the length of counting cycles to vary if the tape is run at a different speed than normal during the recording and permits the speed to be controlled during playback without adversely affecting the phase. The starting count can be determined by counting clock signals between suc-cessive control signals and using the count thus obtained to set the initial count value for counts made during the time between successive pulses from the pulse generator.
ABSTRACT OF THE DISCLOSURE
In video reproducing apparatus having a rotating head, a pulse generator produces pulses synchronously with the rotation of the head. A counter begins counting clock signals at the time of each of the pulses and continues counting until the next pulse. The final count at the end of each counting cycle is converted to an analog signal to control the speed of ro-tation of the head. The phase angle of the head is controlled by control pulses recorded on the tape, which are compared with pulses from the pulse generator to affect incrementally the same speed control mechanism. The starting count of each counting cycle is varied in accordance with the time between successive control signals so that the final count will be the same as long as rotation of the head is synchronous with the control signals. This allows the length of counting cycles to vary if the tape is run at a different speed than normal during the recording and permits the speed to be controlled during playback without adversely affecting the phase. The starting count can be determined by counting clock signals between suc-cessive control signals and using the count thus obtained to set the initial count value for counts made during the time between successive pulses from the pulse generator.
Description
,'~,,i ~ BACKGROUND OF THE I~VENTION
.
Field of the Invention This invention relates to the field of video tape appara-tus and particularly to means for controlling both the phase . ~
. 5 and speed of the rotary head of such apparatus by the same means, such asa brake but wlth means to derive the speed sig-nal independently of the phase signal so that, if the informa--i tion was recorded at a speed different from the customary . ., - speed, the tape can be run at such different speed during play-back without adversely affecting the phase of the rotating - head.
:
~; The Prior Art :;
Video tape apparatus normally includes a supply of tape - on which information signals may have been recorded previously or may be recorded by the apparatus itsel~. The tape is , ~ .
wrapped at least partially around a drum in which a head that includes one or more video transducers is located. The head is supported so that it can rotate to move the transducer :,.
means in a circular path in a plane that intersects the longi-. .
tudinal direction of the helically wrapped tape. The tape is .
~ drawn along this helical path by a capstan that normally oper-,: ~
i ates at a fixed speed. Information signals are recorded in :: :
-~ slant tracks on the surface of the tape, and control signals are recorded by a fixed transducer along one edge of the tape.
Both the information signals and the control signals are re-corded while the tape is moving and so their actual positions :~..-.
on the tape are determined by the speed at which the tape is moving. Thelcontrol signals may be derived from pulses gene-rated in a magnetic pick-up device located adjacent the rotary ,-.~i .",.~
.
Field of the Invention This invention relates to the field of video tape appara-tus and particularly to means for controlling both the phase . ~
. 5 and speed of the rotary head of such apparatus by the same means, such asa brake but wlth means to derive the speed sig-nal independently of the phase signal so that, if the informa--i tion was recorded at a speed different from the customary . ., - speed, the tape can be run at such different speed during play-back without adversely affecting the phase of the rotating - head.
:
~; The Prior Art :;
Video tape apparatus normally includes a supply of tape - on which information signals may have been recorded previously or may be recorded by the apparatus itsel~. The tape is , ~ .
wrapped at least partially around a drum in which a head that includes one or more video transducers is located. The head is supported so that it can rotate to move the transducer :,.
means in a circular path in a plane that intersects the longi-. .
tudinal direction of the helically wrapped tape. The tape is .
~ drawn along this helical path by a capstan that normally oper-,: ~
i ates at a fixed speed. Information signals are recorded in :: :
-~ slant tracks on the surface of the tape, and control signals are recorded by a fixed transducer along one edge of the tape.
Both the information signals and the control signals are re-corded while the tape is moving and so their actual positions :~..-.
on the tape are determined by the speed at which the tape is moving. Thelcontrol signals may be derived from pulses gene-rated in a magnetic pick-up device located adjacent the rotary ,-.~i .",.~
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~14~ 6 shaft of the rotary transducers to éorrelate the speed and phase angle of the rotating head and the speed and linear ~ position of the tape.
: During playback of the recorded tape, the same type of ~ 5 pulse generator produces pulses according to the speed of ro-- tation of the magnetic transducers. These pulses also indi-cate a specific angular, or phase position of the rotating head at the time each pulse is generatedO These pulses are compared with signals produced from the control pulses record~
. lO ed along the tape to determine the relative position, or phase, i~- of the rotating head and the linear position of the tàpe.
. The information thus derived is applied to a brake to slow down the rotation of the transducers to a greater or less de-. gree as necessary to cause the head to rotate relative to the -~ 15 control signals so that the transducers will always start to :: scan a slant area of the tape at a point that corresponds to ~ .:
.~ the start of one of the slant tracks.
~;; The apparatus further includes means to use the pulses :,-:-.` generated to produce a signal responsive to the speed of rota-~- 20 tion of the head so that the slant areas traversed by the :
: transducers will not only start a* the same point as the beg-- ginning of each of the slant tracks previously recorded, but ~- will continue directly along each of the slant tracks. The .~ speed control requires a further comparison of signals derived from the pulse generator and the control signals. Both the speed responsive signal and the phase responsive signal are applied to the brake mechanism to aff~ct its operation.
If the information signals were recorded in a mechanism . in which the rotating transducers were turning at a fa.ster speed than 303z, for example 30 l~z, the spacing between con-., ., ~ .
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~ trol pulses recorded along the edge of the tape would be i~ changed correspondingly from the normal spacing between such ~`- pulses. In order for the tape recorded at this incorrect speed to be played back, the speed responsive signal must be used to control the speed of rotation of the rotary trans--` ducers in the playback mechanism. However, the speed respon-- sive signal for a higher speed is lower in magnitude than the speed responsive signal for a lower speed. This signal of different magnitude, when applied to the brake, adjusts the -- 10 brake pressure to cause the head to rotate at the required ~ synchronous speed to reproduce information on the tape. Since -~ the brake responds not only to the speed responsive signal .
but also to the phase responsive signal, a change in the ,:
: speed responsive signal offsets the phase condition and, al-. 15 though the speed may be changed to the required different synchronous speed, the phase is likely to be offset so that ~-- the transducers will not scan precisely the correct slant ` track areas but will scan areas that are somewhat offset when the apparatus is required to operate at a speed other ;,~, 20 than the normal 3~0~z-~-speed.
.,. ~ :
It is one of the objects of the present invention to separate the effects of the speed responsive signal and the phase responsive signal so that tapes can be played back at a required different synchronous speed than is customary, without adversely affecting the phase condition of the rotary head.
SUMMARY OF T~IE INVENTION
;~ In accordance with the present invention pulse signals -~ generated from the apparatus associated with the rotating head control a counter that counts the number of clock signals ',' ''' ..
, . between successive signals from the pulse generator. The re-sulting final count oE each counting cycle is converted to an analog signal that represents the rotational speed of the . head, and this signal is used to control the speed to the proper value.
Instead of having the count start over at zero in each . counting cycle and count to a number that depends on the speed, which in turn depends on the time between successive :. recorded control signals, the initial count may be made de-pendent on the time between successive control signals so that, if the speed is synchronous, the counter will always :~ count to the same final number, which will be converted into ., .~ a constant analog value. Thus, a change in the speed, such . as is required to obtain the necessary synchronous operation, , .
-- 15 will not affect the phase relationship, and the phase angle . of the head relative to a linear position of the tape will be controlled independently of the speed control although the -. same mechanism is affected by both the speed and phase con-.~` trol signals.
More particularly there is provided in an apparatus for reproducing information signals recorded in successive paral-~; lel tracks on a record medium along with respective control . signals recorded on the record medium in predetermined posi-tional relationship to said tracks, and in which the appara-tus includes rotary transducer means for scanning said tracks in succession so as to reproduce the information signals re-corded therein as the record medium is advanced, and fixed transducer means for reproducing said control signals with a repetition rate that is dependent on the speed of advancement . ~
`. 30 of the record medium: a speed and phase control system for .~ said rotary transducer means-comprising rotational speed de-. ~ - 5 -:
.,',:
, ; tector means for producing pulse signals representative of the rotational position of said rotary transducer means and having a repetition rate that is a function of the rotational speed of said rotary transducer means; phase comparison means for producing a phase responsive signal having a voltage ,~ level that is varied in response to changes in the relative timing of said reproduced control signals and said pulse sig-nals; means for producing a speed responsive signal including a source of clock pulses, counting means for counting said -` 10 clock pulses for time intervals determined by said repetition rate of said pulse signals from the rotational speed detector means, means for converting the count of said counting means, at the end of each of said time intervals, to a corresponding voltage level of said speed responsive signal, and means for establishing the initial count of said counting means a-t the , commencement of each of said time intervals in dependence on ,~- said repetition rate of said reproduced control signals so that the voltage level of said speed responsive signal is ~, varied in response to changes in said repetition rate of the -- 20 pulse signals only when said changes occur without correspond-ing changes in said repetition rate of the reproduced control signals; and means for controlling the rotation of said ro-tary transducer means in response to the voltage levels of ; said phase responsive signal and said speed responsive signal BRIEF DESCRIPTION OF THE DR~WINGS
Fig. 1 is a block diagram of a conventional phase and speed servo loop.
Fig. 2A and 2B show the relationships between pulse sig-nals in the conventional phase and speed servo loop of Fig. 1 Fig. 3 is a block diagram of a speed responsive circuit according to this invention.
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~ Fig. 4 is a block diagram of the combination of an auto-- matic preset circuit according to this invention and the ro-. . .
tational speed responsive circuit of Fig. 3.
; Fig. 5, appearing with Fig. 3, shows waveforms obtained in the operation of the circuits in Figs. 3 and 4.
Fig. 6A and Fig. 6B show waveforms ~f signals illustrat-ing operation of the preset circuit in Fig. 4.
Fig. 7, appearing with Fig. ~, is a schematic block dia-gram of a control system according to this invention.
.... .
-` The prior art control circuit in Fig. 1 represents sche-matically only the speed responsive and phase responsive sec-tions of apparatus such as is used in video tape playback de-' vices to reproduce video signals recorded on tape. Such sig-~ 15 nals are normally recorded in slant tracks relative to the longitùdinal direction of the tape and are accompanied by control signals recorded along one edge of the tape and de-signated as CTL signals. The CTL signals are recorded to ~ provide an indication of the angular position of the rotating ; 20 head, which is used in both the recording and playback appa-ratus relative to the instantaneous linear position of the ~-tape being acted upon by that apparatus.
In Fig. 1 the reproduced CTL signals are applied by way , ~ . .
of an input terminal 11 to a comparison circuit 12. The out-put of the comparison circuit 12 is applied to an error signal generator 15O The output of the error signal generator is, .,, . ~ .
in turn, applied to a control circuit 13 connected to a ro-`;,tating assembly 14. The rotat~ing assembly includes a rotary ... . . .
head, a motor to drive the head, and a brake to govern the ...
speed of rotation of the head. A pulse generator 16 usually .; .
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, in the form of a maynetic pick-up coil, is actuated by the ;
rotating assembly 14. Normally this is accomplished by A
magnet on the shaft between the brake mechanism and the ro--- tary headO Once each revolution of the shaft, the field of ' ~ 5 the magnet intersects the pick-up coil and produces a pulse - voltage that identifies the shaft as having a certain angular -~ position at the time the pulse is generated.
. .
'~ Two control loops s and _ are connected to the pulse ~<~- generator 16. The control loop s controls the speed of the ` 10 rotating assembly 14 and applies pulses identified as PG sig-nals from the pulse generator 16 to a phase converter 17 that ; has a conversion factor -kl. The output of converter 17is connected to the circuit 13. The phase control loop _ in-cludes an integrating circuit 18 connected to the pulse gene-rator 16 and having an output signal connected to the com-parison circuit 12.
uring normal operation of the apparatus, the ro-tating assembly 14 operates at a constant, designated speed, which : ,.
`~ is usually 30 revolutions per second. The pulses from the :
pulse generator 16 are converted by the converter 17 to a feedback voltage es applied to the circuit 13. At the same time the pulses from the pulse generator 16 are integrated by the integrating circuit 18 and applied to the comparison circuit 12 to be compared with control pulses of the input control signal applied to the terminal 11. The resulting com-parison signal actuates the error voltage generator 15 to generate a phase responsive signal ep. This signal is com-bined in the circuit 13 with the speed responsive signal es ~; to generate a braking signal _ to be applied to the brake in the rotating assembly 14.
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A typical relative timing between the control pulses ap-plied to the input terminal ll and the pulses generated by the pulse generator PG when the speed of rotation of the recording head is correct is shown in Fig. 2A. As indicated, . 5 the speed of rotation is 30Hz and the difference in timing -~ between the control pulses and the pulses from the pulse gene-rator is indicated by ~. When the apparatus is operating cor-rectly the relative timing difference ~ causes the production `- of a certain value of the phase responsive voltage e and the proper rotating speed causes the production of a certain speed responsive voltage es. The combination of the phase responsive voltage and the speed responsive voltage causes a certain voltage e to be applied to the brake in the rotary assembly 14, to keep both the phase and the speed of rotation : . 15 correct.
If the rotating speed of the rotating assembly 14 is varied, for example by being slowed down momentarily, the voltage es and the voltage ep both change to act upon the brake in the rotating assembly 14 to bring the operation back to the correct phase and speed relationships.
However, if the information was originally recorded on the tape with an incorrect rotating speed of the rotary head, a different set of phase conditions results. These conditions .;
are illustrated in Fig. 2B for a rotating speed of 30.lHz.
V 25 The control pulses are spaced incrementally closer together `~ than in the case where the speed was correct, and the pulse,. . .
generator pulses are also spaced in a corresponding manner as :, ~ is required by the fact that the speed of rotation of the .
rotating assembly 14 must be synchronous with the repetition ` 30 rate of the control pulses. The voltage es changes with the ,. -l - 8 -, .......... .
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:' increase of the rotational speed ~ of the rotating assembly ' 14, but since this speed ~ is necessarily higher in order to follow the recorded signals, the voltage applied to -the brake ; in the rotating assembly 14 must be constant and thus the phase responsive signal ep compensates for the change of the speed responsive feedback voltage e . To obtain the compen-- s sation voltage, a phase difference ~' is created between the control signal and the PG signal~ As a result/ the rotary , . . .
head in the assembly 14 cannot accurately scan the tracks on the magnetic tape.
. ~
Fig. 3 shows a circuit for generating a speed responsive signal using digital circuits. Pulses PG from a pulse genera-tor such as the pulse generator 16 in Fig. 1 are applied to an --- input terminal 19 connected to three four-bit counters 21-23.
Clock pulse CP having a much higher repetition rate than the ,.
` pulses PG are applied to another input terminal 24, which is connected to the counters 21-23. The counters also have a number of preset terminals Po~Pll, one for each of the four bits of each counter.
Output terminals of the counters 21-23 axe connected to :'.~.;
respective hold circuits 26-28 to which the pulses PG are also connected by way of an input terminal l9a. The hold circuits , 26~28 have four-bit output terminals corresponding to the four-~' bit output terminals of the counters 21~23, and the output -~ 25 terminals of the hold circuits are connected to suitable in-put terminals of a digital-to-analog (D/A) converter 29. This converter has an output terminal 31 from which the speed re-:.:.
~' sponsive signal es is obtained.
; The operation of the circuit in Fig. 3 will first be considered with respect to the signals represented by the wave-. .
,~ _ g , , - . .
, forms in Fig. 5. Fig. 5(a) represents the pulse signals PG
- from the pulse generator 16 in Fig. 1 when the time between -: . .
successive ones of these pulses increases. The clock pulses ;~ CP applied to the input terminal 24 are counted by the count-ers 21-23. This counting is actually binary coùnting but is represented in Fig. 5(b) as if each clock pulse produced an incremental increase in the voltage level and was returned to zero at the occurrence of each pu~se PG. The level returns to zero because it is considered for the moment that the pre-set starting count levels applied to the terminals Po~Pll are - zero. The increments may be considered so small and the clock pulse frequency so high that the voltage level appears to increase smoothly Between the first pulse PGl and the second pulse PG2 the ~ 15 voltage level rises to a certain value that may be considered the standard value. Between pulses PG2 and PG3 the rotating assembly 14 in Fig. 1 starts to slow down and so the voltage ; level has time to build up to a higher level as the counters ' 21-23 count to a larger number. This continues during the ;;
intervals from the pulse PG3 to the pulse PG4 and from the pulse PG4 to the pulse PG5.
~` The peak values of the count at the end of each counting - cycle are converted by the D/A converter 29 to a voltage re-presented by the step wave in Fig. 5(c). Corresponding to ,-- 25 the increasing counts, the level of the speed responsive volt-~, age es increases. This increasing voltage would act on the brake in the rotating assembly 14 in Fig. 1 to release the `~ brake enough to speed up the rotation.
If the starting count values applied to the terminals ` 30 Po~Pll are different from zero, the counters 21 23 will, ;~ !
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within the same counting cycles illustrated in Fig. 5, count `~ to a different maximum level. Whatever the starting count level, the final count in each cycle will change if the ro-tating assembly 14 in Fig. 1 momentarily changes speed.
- 5 Fig. 4 shows a circuit to preset the starting count levels of the counters 21-23, which are the same as in Fig. 3, to a value that depends on the length of time between successive CTL pulses. This permits the system to handle tapes record-ed with the rotary head rotating at speeds somewhat different from the standard 30Hz speed.
In Fig. 4, the control pulses are applied via an input terminal 32 to three four-bit counters 33-35. These counters ; also have preset terminals 37-39 and a clock signal input terminal 24a. The four-bit output terminals of the counters ~ 15 33-35 are connected to respective input terminals of three -~ hold circuits 41-43. The CTL pulses are also applied through an input terminal 32a. Separate inverters, 44-55 connect the respective four output terminals of the hold circuits 41-43 to the automatic preset terminals Po~Pll of the counters 21-23. The lower part of the circuit in Fig. 4 is identical with , the circuit in Fig. 3.
The operation of the circuit in Fig. 4 will be described with respect to waveforms in Figs. 6A and 6B. The waveform (a) in Fig. 6A represents the CTL pulses at the normal repe-. ~
` 25 tition rate of 30Hz. The waveform (b) represents the CTL
pulses recorded at a high repetition rate, which is indicated as 30.1~1z. The preset terminal~ 37-39 are all set to the same starting value n' and, as the counting of the clock - pulses CP takes place during each counting cycle, the output signals from the counters 33-35 decrease, in effect. IE the -'~ - 11 -.
, .
CTL frequency is 30Hz, the count value decreases to nl along the line a. If the CTL frequency is 30.1~z, the count value only decreases to the level n2.
The final count value, whatever its level may be, of each cycle is applied to the preset terminals Po~Pll to determine corresponding starting count leve:Ls of the counters 21-23. As - illustrated in the waveforms (c) in Fig. 6A, the 30Hz CTL
pulse causes the counters 33-35 to count to the level nl, which produces a starting count level nOl in the counters 21-23. The count level n2 for 30.1Hz CTL pulses produces a starting count level nO2. In each case, the counters 21-23 : . .
count to the same final level n. As a result the speed re-sponsive signal es does n~t change for tape recorded at a different speed, but it does change in the manner previously described if the speed of the rotating mechanism in the play-back device changes momentarily.
.
i Fig. 7 schematically shows a control circuit that pro-duces the effects according to this invention. Many of the components are similar to those in Fig. 1 and have been given the same reference numerals. The speed control loop s includes ; a speed comparator 56 which has one input terminal connected -~ to the pulse generator 16. A differentiating cirauit 57 connects the CTL signal input terminal 11 to a second input terminal of the speed comparator 56. The output terminal of , 25 the comparator 56 is connected to the converter 17 to produce a speed responsive signal es, and the error signal generator ,~., .
15 and converter 17 supply the phase responsive signal ep and the speed responsive signal es to the control circuit 13.
In the operation of the circuit in Fig. 7 since the ~; 30 repetition rate of the PG signal from the pulse generator 16 :;
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~0~8~6 varies with the repetition rate of the CTL signal pulses, - the speed responsive signal es does not change if the record-- int speed dhanges. Therefore, the value of the voltage _ applied to the brake in the rotating assembly 14 remains constant unless the speed of the rotating assembly varies from the speed required by the CTI. pulse signal.
; Although this invention has been described with respect to the speed and phase control system for a rotary head drum having video magnetic transducing means, this invention can be applied to thP speed and phase control system for the capstan. Also, the CTL signal as the reference signal may be replaced by a signal synchronized by an external vertical .
synchronizing signal. Other changes and modifications can be effected therein by one skilled in the art without depart- r ing from the scope and spirit of the invention as defined in - the appended claims.
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~14~ 6 shaft of the rotary transducers to éorrelate the speed and phase angle of the rotating head and the speed and linear ~ position of the tape.
: During playback of the recorded tape, the same type of ~ 5 pulse generator produces pulses according to the speed of ro-- tation of the magnetic transducers. These pulses also indi-cate a specific angular, or phase position of the rotating head at the time each pulse is generatedO These pulses are compared with signals produced from the control pulses record~
. lO ed along the tape to determine the relative position, or phase, i~- of the rotating head and the linear position of the tàpe.
. The information thus derived is applied to a brake to slow down the rotation of the transducers to a greater or less de-. gree as necessary to cause the head to rotate relative to the -~ 15 control signals so that the transducers will always start to :: scan a slant area of the tape at a point that corresponds to ~ .:
.~ the start of one of the slant tracks.
~;; The apparatus further includes means to use the pulses :,-:-.` generated to produce a signal responsive to the speed of rota-~- 20 tion of the head so that the slant areas traversed by the :
: transducers will not only start a* the same point as the beg-- ginning of each of the slant tracks previously recorded, but ~- will continue directly along each of the slant tracks. The .~ speed control requires a further comparison of signals derived from the pulse generator and the control signals. Both the speed responsive signal and the phase responsive signal are applied to the brake mechanism to aff~ct its operation.
If the information signals were recorded in a mechanism . in which the rotating transducers were turning at a fa.ster speed than 303z, for example 30 l~z, the spacing between con-., ., ~ .
.
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~:`
....
~ trol pulses recorded along the edge of the tape would be i~ changed correspondingly from the normal spacing between such ~`- pulses. In order for the tape recorded at this incorrect speed to be played back, the speed responsive signal must be used to control the speed of rotation of the rotary trans--` ducers in the playback mechanism. However, the speed respon-- sive signal for a higher speed is lower in magnitude than the speed responsive signal for a lower speed. This signal of different magnitude, when applied to the brake, adjusts the -- 10 brake pressure to cause the head to rotate at the required ~ synchronous speed to reproduce information on the tape. Since -~ the brake responds not only to the speed responsive signal .
but also to the phase responsive signal, a change in the ,:
: speed responsive signal offsets the phase condition and, al-. 15 though the speed may be changed to the required different synchronous speed, the phase is likely to be offset so that ~-- the transducers will not scan precisely the correct slant ` track areas but will scan areas that are somewhat offset when the apparatus is required to operate at a speed other ;,~, 20 than the normal 3~0~z-~-speed.
.,. ~ :
It is one of the objects of the present invention to separate the effects of the speed responsive signal and the phase responsive signal so that tapes can be played back at a required different synchronous speed than is customary, without adversely affecting the phase condition of the rotary head.
SUMMARY OF T~IE INVENTION
;~ In accordance with the present invention pulse signals -~ generated from the apparatus associated with the rotating head control a counter that counts the number of clock signals ',' ''' ..
, . between successive signals from the pulse generator. The re-sulting final count oE each counting cycle is converted to an analog signal that represents the rotational speed of the . head, and this signal is used to control the speed to the proper value.
Instead of having the count start over at zero in each . counting cycle and count to a number that depends on the speed, which in turn depends on the time between successive :. recorded control signals, the initial count may be made de-pendent on the time between successive control signals so that, if the speed is synchronous, the counter will always :~ count to the same final number, which will be converted into ., .~ a constant analog value. Thus, a change in the speed, such . as is required to obtain the necessary synchronous operation, , .
-- 15 will not affect the phase relationship, and the phase angle . of the head relative to a linear position of the tape will be controlled independently of the speed control although the -. same mechanism is affected by both the speed and phase con-.~` trol signals.
More particularly there is provided in an apparatus for reproducing information signals recorded in successive paral-~; lel tracks on a record medium along with respective control . signals recorded on the record medium in predetermined posi-tional relationship to said tracks, and in which the appara-tus includes rotary transducer means for scanning said tracks in succession so as to reproduce the information signals re-corded therein as the record medium is advanced, and fixed transducer means for reproducing said control signals with a repetition rate that is dependent on the speed of advancement . ~
`. 30 of the record medium: a speed and phase control system for .~ said rotary transducer means-comprising rotational speed de-. ~ - 5 -:
.,',:
, ; tector means for producing pulse signals representative of the rotational position of said rotary transducer means and having a repetition rate that is a function of the rotational speed of said rotary transducer means; phase comparison means for producing a phase responsive signal having a voltage ,~ level that is varied in response to changes in the relative timing of said reproduced control signals and said pulse sig-nals; means for producing a speed responsive signal including a source of clock pulses, counting means for counting said -` 10 clock pulses for time intervals determined by said repetition rate of said pulse signals from the rotational speed detector means, means for converting the count of said counting means, at the end of each of said time intervals, to a corresponding voltage level of said speed responsive signal, and means for establishing the initial count of said counting means a-t the , commencement of each of said time intervals in dependence on ,~- said repetition rate of said reproduced control signals so that the voltage level of said speed responsive signal is ~, varied in response to changes in said repetition rate of the -- 20 pulse signals only when said changes occur without correspond-ing changes in said repetition rate of the reproduced control signals; and means for controlling the rotation of said ro-tary transducer means in response to the voltage levels of ; said phase responsive signal and said speed responsive signal BRIEF DESCRIPTION OF THE DR~WINGS
Fig. 1 is a block diagram of a conventional phase and speed servo loop.
Fig. 2A and 2B show the relationships between pulse sig-nals in the conventional phase and speed servo loop of Fig. 1 Fig. 3 is a block diagram of a speed responsive circuit according to this invention.
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- 5a -,~
., .
~ Fig. 4 is a block diagram of the combination of an auto-- matic preset circuit according to this invention and the ro-. . .
tational speed responsive circuit of Fig. 3.
; Fig. 5, appearing with Fig. 3, shows waveforms obtained in the operation of the circuits in Figs. 3 and 4.
Fig. 6A and Fig. 6B show waveforms ~f signals illustrat-ing operation of the preset circuit in Fig. 4.
Fig. 7, appearing with Fig. ~, is a schematic block dia-gram of a control system according to this invention.
.... .
-` The prior art control circuit in Fig. 1 represents sche-matically only the speed responsive and phase responsive sec-tions of apparatus such as is used in video tape playback de-' vices to reproduce video signals recorded on tape. Such sig-~ 15 nals are normally recorded in slant tracks relative to the longitùdinal direction of the tape and are accompanied by control signals recorded along one edge of the tape and de-signated as CTL signals. The CTL signals are recorded to ~ provide an indication of the angular position of the rotating ; 20 head, which is used in both the recording and playback appa-ratus relative to the instantaneous linear position of the ~-tape being acted upon by that apparatus.
In Fig. 1 the reproduced CTL signals are applied by way , ~ . .
of an input terminal 11 to a comparison circuit 12. The out-put of the comparison circuit 12 is applied to an error signal generator 15O The output of the error signal generator is, .,, . ~ .
in turn, applied to a control circuit 13 connected to a ro-`;,tating assembly 14. The rotat~ing assembly includes a rotary ... . . .
head, a motor to drive the head, and a brake to govern the ...
speed of rotation of the head. A pulse generator 16 usually .; .
~; 6 .....
.",~ .
' ~ . .
,:
'`'',' ,.:
.
, in the form of a maynetic pick-up coil, is actuated by the ;
rotating assembly 14. Normally this is accomplished by A
magnet on the shaft between the brake mechanism and the ro--- tary headO Once each revolution of the shaft, the field of ' ~ 5 the magnet intersects the pick-up coil and produces a pulse - voltage that identifies the shaft as having a certain angular -~ position at the time the pulse is generated.
. .
'~ Two control loops s and _ are connected to the pulse ~<~- generator 16. The control loop s controls the speed of the ` 10 rotating assembly 14 and applies pulses identified as PG sig-nals from the pulse generator 16 to a phase converter 17 that ; has a conversion factor -kl. The output of converter 17is connected to the circuit 13. The phase control loop _ in-cludes an integrating circuit 18 connected to the pulse gene-rator 16 and having an output signal connected to the com-parison circuit 12.
uring normal operation of the apparatus, the ro-tating assembly 14 operates at a constant, designated speed, which : ,.
`~ is usually 30 revolutions per second. The pulses from the :
pulse generator 16 are converted by the converter 17 to a feedback voltage es applied to the circuit 13. At the same time the pulses from the pulse generator 16 are integrated by the integrating circuit 18 and applied to the comparison circuit 12 to be compared with control pulses of the input control signal applied to the terminal 11. The resulting com-parison signal actuates the error voltage generator 15 to generate a phase responsive signal ep. This signal is com-bined in the circuit 13 with the speed responsive signal es ~; to generate a braking signal _ to be applied to the brake in the rotating assembly 14.
` .': f ~ - 7 -:, , .,, ", , ~
~;.
A typical relative timing between the control pulses ap-plied to the input terminal ll and the pulses generated by the pulse generator PG when the speed of rotation of the recording head is correct is shown in Fig. 2A. As indicated, . 5 the speed of rotation is 30Hz and the difference in timing -~ between the control pulses and the pulses from the pulse gene-rator is indicated by ~. When the apparatus is operating cor-rectly the relative timing difference ~ causes the production `- of a certain value of the phase responsive voltage e and the proper rotating speed causes the production of a certain speed responsive voltage es. The combination of the phase responsive voltage and the speed responsive voltage causes a certain voltage e to be applied to the brake in the rotary assembly 14, to keep both the phase and the speed of rotation : . 15 correct.
If the rotating speed of the rotating assembly 14 is varied, for example by being slowed down momentarily, the voltage es and the voltage ep both change to act upon the brake in the rotating assembly 14 to bring the operation back to the correct phase and speed relationships.
However, if the information was originally recorded on the tape with an incorrect rotating speed of the rotary head, a different set of phase conditions results. These conditions .;
are illustrated in Fig. 2B for a rotating speed of 30.lHz.
V 25 The control pulses are spaced incrementally closer together `~ than in the case where the speed was correct, and the pulse,. . .
generator pulses are also spaced in a corresponding manner as :, ~ is required by the fact that the speed of rotation of the .
rotating assembly 14 must be synchronous with the repetition ` 30 rate of the control pulses. The voltage es changes with the ,. -l - 8 -, .......... .
'.,~
... .
; ' , . ' . . ! ;. .:.
'-',': " .
:' increase of the rotational speed ~ of the rotating assembly ' 14, but since this speed ~ is necessarily higher in order to follow the recorded signals, the voltage applied to -the brake ; in the rotating assembly 14 must be constant and thus the phase responsive signal ep compensates for the change of the speed responsive feedback voltage e . To obtain the compen-- s sation voltage, a phase difference ~' is created between the control signal and the PG signal~ As a result/ the rotary , . . .
head in the assembly 14 cannot accurately scan the tracks on the magnetic tape.
. ~
Fig. 3 shows a circuit for generating a speed responsive signal using digital circuits. Pulses PG from a pulse genera-tor such as the pulse generator 16 in Fig. 1 are applied to an --- input terminal 19 connected to three four-bit counters 21-23.
Clock pulse CP having a much higher repetition rate than the ,.
` pulses PG are applied to another input terminal 24, which is connected to the counters 21-23. The counters also have a number of preset terminals Po~Pll, one for each of the four bits of each counter.
Output terminals of the counters 21-23 axe connected to :'.~.;
respective hold circuits 26-28 to which the pulses PG are also connected by way of an input terminal l9a. The hold circuits , 26~28 have four-bit output terminals corresponding to the four-~' bit output terminals of the counters 21~23, and the output -~ 25 terminals of the hold circuits are connected to suitable in-put terminals of a digital-to-analog (D/A) converter 29. This converter has an output terminal 31 from which the speed re-:.:.
~' sponsive signal es is obtained.
; The operation of the circuit in Fig. 3 will first be considered with respect to the signals represented by the wave-. .
,~ _ g , , - . .
, forms in Fig. 5. Fig. 5(a) represents the pulse signals PG
- from the pulse generator 16 in Fig. 1 when the time between -: . .
successive ones of these pulses increases. The clock pulses ;~ CP applied to the input terminal 24 are counted by the count-ers 21-23. This counting is actually binary coùnting but is represented in Fig. 5(b) as if each clock pulse produced an incremental increase in the voltage level and was returned to zero at the occurrence of each pu~se PG. The level returns to zero because it is considered for the moment that the pre-set starting count levels applied to the terminals Po~Pll are - zero. The increments may be considered so small and the clock pulse frequency so high that the voltage level appears to increase smoothly Between the first pulse PGl and the second pulse PG2 the ~ 15 voltage level rises to a certain value that may be considered the standard value. Between pulses PG2 and PG3 the rotating assembly 14 in Fig. 1 starts to slow down and so the voltage ; level has time to build up to a higher level as the counters ' 21-23 count to a larger number. This continues during the ;;
intervals from the pulse PG3 to the pulse PG4 and from the pulse PG4 to the pulse PG5.
~` The peak values of the count at the end of each counting - cycle are converted by the D/A converter 29 to a voltage re-presented by the step wave in Fig. 5(c). Corresponding to ,-- 25 the increasing counts, the level of the speed responsive volt-~, age es increases. This increasing voltage would act on the brake in the rotating assembly 14 in Fig. 1 to release the `~ brake enough to speed up the rotation.
If the starting count values applied to the terminals ` 30 Po~Pll are different from zero, the counters 21 23 will, ;~ !
.. i -- 1 0 i:.
.
';'' .';' ' ' ' ' ' ' ' :~
',: ' . ... ' . ,, :
within the same counting cycles illustrated in Fig. 5, count `~ to a different maximum level. Whatever the starting count level, the final count in each cycle will change if the ro-tating assembly 14 in Fig. 1 momentarily changes speed.
- 5 Fig. 4 shows a circuit to preset the starting count levels of the counters 21-23, which are the same as in Fig. 3, to a value that depends on the length of time between successive CTL pulses. This permits the system to handle tapes record-ed with the rotary head rotating at speeds somewhat different from the standard 30Hz speed.
In Fig. 4, the control pulses are applied via an input terminal 32 to three four-bit counters 33-35. These counters ; also have preset terminals 37-39 and a clock signal input terminal 24a. The four-bit output terminals of the counters ~ 15 33-35 are connected to respective input terminals of three -~ hold circuits 41-43. The CTL pulses are also applied through an input terminal 32a. Separate inverters, 44-55 connect the respective four output terminals of the hold circuits 41-43 to the automatic preset terminals Po~Pll of the counters 21-23. The lower part of the circuit in Fig. 4 is identical with , the circuit in Fig. 3.
The operation of the circuit in Fig. 4 will be described with respect to waveforms in Figs. 6A and 6B. The waveform (a) in Fig. 6A represents the CTL pulses at the normal repe-. ~
` 25 tition rate of 30Hz. The waveform (b) represents the CTL
pulses recorded at a high repetition rate, which is indicated as 30.1~1z. The preset terminal~ 37-39 are all set to the same starting value n' and, as the counting of the clock - pulses CP takes place during each counting cycle, the output signals from the counters 33-35 decrease, in effect. IE the -'~ - 11 -.
, .
CTL frequency is 30Hz, the count value decreases to nl along the line a. If the CTL frequency is 30.1~z, the count value only decreases to the level n2.
The final count value, whatever its level may be, of each cycle is applied to the preset terminals Po~Pll to determine corresponding starting count leve:Ls of the counters 21-23. As - illustrated in the waveforms (c) in Fig. 6A, the 30Hz CTL
pulse causes the counters 33-35 to count to the level nl, which produces a starting count level nOl in the counters 21-23. The count level n2 for 30.1Hz CTL pulses produces a starting count level nO2. In each case, the counters 21-23 : . .
count to the same final level n. As a result the speed re-sponsive signal es does n~t change for tape recorded at a different speed, but it does change in the manner previously described if the speed of the rotating mechanism in the play-back device changes momentarily.
.
i Fig. 7 schematically shows a control circuit that pro-duces the effects according to this invention. Many of the components are similar to those in Fig. 1 and have been given the same reference numerals. The speed control loop s includes ; a speed comparator 56 which has one input terminal connected -~ to the pulse generator 16. A differentiating cirauit 57 connects the CTL signal input terminal 11 to a second input terminal of the speed comparator 56. The output terminal of , 25 the comparator 56 is connected to the converter 17 to produce a speed responsive signal es, and the error signal generator ,~., .
15 and converter 17 supply the phase responsive signal ep and the speed responsive signal es to the control circuit 13.
In the operation of the circuit in Fig. 7 since the ~; 30 repetition rate of the PG signal from the pulse generator 16 :;
,:
~ - 12 -,~ .
~;".
, .:' ' ' ' . . .
~0~8~6 varies with the repetition rate of the CTL signal pulses, - the speed responsive signal es does not change if the record-- int speed dhanges. Therefore, the value of the voltage _ applied to the brake in the rotating assembly 14 remains constant unless the speed of the rotating assembly varies from the speed required by the CTI. pulse signal.
; Although this invention has been described with respect to the speed and phase control system for a rotary head drum having video magnetic transducing means, this invention can be applied to thP speed and phase control system for the capstan. Also, the CTL signal as the reference signal may be replaced by a signal synchronized by an external vertical .
synchronizing signal. Other changes and modifications can be effected therein by one skilled in the art without depart- r ing from the scope and spirit of the invention as defined in - the appended claims.
:
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;' , . , :, : . , :
,,~ ~ ,.
.,,1 ,', ';
.
: .
.".
~ - 13 -;' :
., : i.
... . . ..
., ~ ' ' ' : , " ' " ' ' ', . .
Claims (6)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. In an apparatus for reproducing information signals recorded in successive parallel tracks on a record medium along with respective control signals recorded on the record medium in predetermined positional relationship to said tracks, and in which the apparatus includes rotary transducer means for scanning said tracks in succession so as to reproduce the information signals recorded therein as the record medium is advanced, and fixed transducer means for reproducing said control signals with a repetition rate that is dependent on the speed of advancement of the record medium: a speed and phase control system for said rotary transducer means comprising rotational speed detector means for producing pulse signals representative of the rotational position of said rotary transducer means and having a repetition rate that is a function of the rotational speed of said rotary transducer means; phase comparison means for producing a phase responsive signal having a voltage level that is varied in response to changes in the relative timing of said reproduced control sig-nals and said pulse signals; means for producing a speed respon-sive signal including a source of clock pulses, counting means for counting said clock pulses for time intervals determined by said repetition rate of said pulse signals from the rotational speed detector means, means for converting the count of said counting means, at the end of each of said time intervals, to a corresponding voltage level of said speed responsive signal, and means for establishing the initial count of said counting means at the commencement of each of said time intervals in dependence on said repetition rate of said reproduced control signals so that the voltage level of said speed responsive signal is varied in response to changes in said repetition rate of the pulse signals only when said changes occur without corresponding changes in said repetition rate of the reproduced control signals; and means for controlling the rotation of said rotary transducer means in response to the voltage levels of said phase responsive signal and said speed responsive signal.
2. An apparatus according to claim 1, wherein said means for controlling the rotation of said rotary transducer means comprises braking means for braking said rotary transducer means.
3. An apparatus according to claim 2, wherein said means for controlling the rotation of said rotary transducer means further comprises an adder connected to said phase comparison means and to said means for converting the count of said counting means, the output of said adder being connected to said braking means for regulating the latter.
4. An apparatus according to claim l; wherein said counting means includes a first digital counter, and said means for converting the count includes a digital-analog converter.
5. An apparatus according to claim 4; wherein said means' for establishing the initial count of said counting means includes a second digital counter for counting said clock pulses for time intervals determined by said repetition rate of said reproduced control signals and correspondingly establishing said initial count of the first digital counter.
6. An apparatus according to claim 1, in which the record medium is in the form of a tape which is advanced longitudinally and has said successive parallel tracks extending obliquely thereacross, said information signals are video signals having predetermined intervals thereof recorded in said successive tracks, respectively, said rotary transducer means includes a rotary drum having the tape guided in a helical path about a portion of the drum periphery and at least one reproducing head on said drum to repeatedly scan across the tape in said path, and said means for controlling the rotation of the rotary transducer means includes braking means for braking the rotation of said drum and each said head and an adder receiving said phase responsive signal and said speed responsive signal for producing a brake control signal by which the braking force of said braking means is regulated.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP48110338A JPS5062008A (en) | 1973-10-01 | 1973-10-01 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1048146A true CA1048146A (en) | 1979-02-06 |
Family
ID=14533209
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA210,385A Expired CA1048146A (en) | 1973-10-01 | 1974-09-30 | Speed and phase control system |
Country Status (6)
| Country | Link |
|---|---|
| JP (1) | JPS5062008A (en) |
| CA (1) | CA1048146A (en) |
| FR (1) | FR2246933B1 (en) |
| GB (1) | GB1484715A (en) |
| IT (1) | IT1021674B (en) |
| NL (1) | NL7412983A (en) |
Families Citing this family (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS54102474A (en) * | 1978-01-27 | 1979-08-11 | Sony Corp | Digital servo circuit |
| US4355266A (en) * | 1980-07-31 | 1982-10-19 | Ampex Corporation | Eddy current servo system for controlling the rotation of disk packs |
| KR930007793B1 (en) * | 1991-01-09 | 1993-08-19 | 삼성전자 주식회사 | Method of detecting tape driving speed in vtr |
-
1973
- 1973-10-01 JP JP48110338A patent/JPS5062008A/ja active Pending
-
1974
- 1974-09-30 CA CA210,385A patent/CA1048146A/en not_active Expired
- 1974-09-30 GB GB42388/74A patent/GB1484715A/en not_active Expired
- 1974-10-01 IT IT53297/74A patent/IT1021674B/en active
- 1974-10-01 NL NL7412983A patent/NL7412983A/en not_active Application Discontinuation
- 1974-10-01 FR FR7433085A patent/FR2246933B1/fr not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| DE2446817B2 (en) | 1977-01-20 |
| NL7412983A (en) | 1975-04-03 |
| IT1021674B (en) | 1978-02-20 |
| FR2246933B1 (en) | 1983-08-19 |
| DE2446817A1 (en) | 1975-08-21 |
| FR2246933A1 (en) | 1975-05-02 |
| JPS5062008A (en) | 1975-05-27 |
| GB1484715A (en) | 1977-09-01 |
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