ROTATION CONTROL DEVICE

1 2

ROTATION CONTROL DEVICE of the kind comprising a magnetic tape and a rotary head as

sembly including therein a plurality of magnetic transducers This invention relates to a rotation control device which is for the recording and reproduction of a wide-band signal, in effective for use in a magnetic recording and reproducing ap- which an AC synchronous motor driven by a commercial paratus of the rotary head type. Generally speaking, the 5 power supply is employed to serve as a common drive means present invention contemplates the provision of a rotation for the rotary head assembly and the magnetic tape, and a control device for use in an apparatus of the kind comprising a stepless speed change mechanism is employed to connect the magnetic tape and a rotary head assembly including a plurality common drive means with the shaft of the rotary head asof magnetic transducers for the recording and reproduction of sembly thereby facilitating the desired control of the rotation a wide-band signal, in which, in lieu of a complex and expen- 10 of the rotary head assembly and the magnetic tape with a suffisive structure well known in the art which includes therein in- cient degree of precision.

dividual exclusive motors and associated power amplifiers for Another object of the present invention is to provide a rota

separately driving the magnetic tape and the rotary head as- tion control device for use in an apparatus of the abovesembly, a single motor which is driven from a commercial described character, in which an AC synchronous motor power supply is employed to drive both the magnetic tape and 15 driven by a commercial power supply is employed to serve as a the rotary head assembly, and a unique stepless speed change common drive means for the magnetic tape and the rotary mechanism whose speed change ratio can precisely be con- head assembly, and a unique stepless speed change trolled by a very slight electrical power is operatively inter- mechanism whose speed change ratio can be precisely conposed between the motor and the shaft of the rotary head as- trolled by a very slight electrical power is interposed between sembly. 20 t^e common drive means and the shaft of the rotary head as

In a prior method of magnetic recording in which a signal sembly so that during the record mode the rotary head assuch, for example, as a television signal having extremely high sembly can be driven in a synchronous relation with a frequencies or ranging over an extremely wide frequency band reference signal delivered from a reference signal source havis directly recorded on a magnetic tape, the relative speed ing a periodicity thereby forming the desired tracks of record between a recording or reproducing head and a magnetic on the magnetic tape.

recording medium moving past the head gap had to be very A further object of the present invention is to provide a

high in order to satisfactorily record or reproduce the high rotation control device for use in an apparatus of the abovefrequency components of the signal. On the other hand, the described character adapted for the recording and reproducmagnetic recording medium such, for example, as a magnetic ^ tion of a television signal, in which the synchronizing signal in tape was requested to run at a normal low speed. As a com- the television signal having been recorded along one edge of promise for satisfying both these contradictory conditions, the the magnetic tape during the record mode is reproduced from desired purpose for obtaining a relatively high speed between the magnetic tape during the playback mode so that the the magnetic tape and the recording head was obtained by reproduced signal can be utilized as a reference signal for drivcausing the magnetic head to mechanically rotate at a high 35 ing the rotary head assembly for the reproduction of the tracks speed transversely across the magnetic tape. In U.S. Pat. No. of record of the television signal provided on the magnetic 2,916,546, for example, a rotary head assembly having a drum tape.

including therein four magnetic transducers is provided and a Another object of the present invention is to provide a rota

magnetic tape is advanced perpendicular to the plane of rota- tion control device for use in an apparatus of the abovetion of the rotary head, and a guide means cups the tape for 40 described character adapted for the recording and reproduccontact with the transducer units. More precisely, the mag- tion of a television signal, in which an AC synchronous motor netic tape is driven past the head in its longitudinal direction driven by a commercial power supply is employed to serve as a at a speed of 15 inches per second and a video signal is common drive means for the rotary head assembly and the recorded in the form of a series of transverse lines or tracks. magnetic tape, the common drive means being connected with

In a magnetic recording and reproducing apparatus having 45 the shaft of the rotary head assembly through a unique stepless such a rotary head, the rotating speed or the phase of rotation speed change mechanism whose speed change ratio can be of the rotary head was controlled, if so required, by comparing precisely controlled by a very slight electrical power, and dura signal which is dependent upon the rotation of the rotary ing the record mode, the rotary head assembly is driven in a head with a reference signal to derive an error signal synchronous relation with a control signal responsive to the therebetween, and utilizing the error signal to control the rota- 50 synchronizing signal in the television signal to be recorded tion of the rotary head. Further, in view of the requirement ac- thereby forming the tracks of record of the television signal on cording to which a specific relationship had to be established the magnetic tape and at the same time recording the between the running speed of the magnetic tape and the rotat- synchronizing signal in the television signal on one edge of the ing speed of the rotary head in the case of reproduction, a magnetic tape, while during the playback mode, the signal representing the running speed of the tape was com- 55 synchronizing signal having been recorded on one edge of the pared with a signal which is dependent upon the rotation of magnetic tape is reproduced and is utilized as a reference the rotary head to thereby derive an error signal signal so that a very slight electrical power representing an therebetween, and the error signal was utilized to control the error between the phase of the reference signal and the phase rotation of the tape drive motor. As another prior example of a signal responsive to the rotation of the rotary head asknown in the art, U.S. Pat. No. 3,293,359 disclose a method in 60 sembly is used to control the stepless speed change which a magnetic tape was helically driven to wrap up the sub- mechanism which controls the rotation of the rotary head asstantially half periphery of a cylindrical tape guide, and a ro- sembly, which is operative to reproduce the tracks of record tary head assembly accommodated in the cylindrical tape of the television signal provided on the magnetic tape, guide made sliding contact with the tape through a slit extend- The above and other objects, advantages and features of the

ing over the entire periphery of the cylindrical tape guide, 65 present invention will become apparent from the following thereby forming a series of skewed tracks on the tape. description, in which preferred embodiments of the present

From the two prior examples described above, it will be invention are described in detail with reference to the accomrecognized that the rotary head assembly and the magnetic panying drawings, tape must be driven at a very precisely controlled speed. How- In the drawings:

ever, the drive system for the magnetic tape and the rotary 70 FIG. 1 is a plan view of a magnetic tape recording and head assembly in the prior art apparatus has been defective in reproducing apparatus having a rotation control device emits complexity, expensiveness and large size. bodying the present invention;

Having the prior defects as pointed out above in mind, it is FIG. 2 is a diagrammatic view showing a series of tracks of a

the primary object of the present invention to provide a novel high frequency signal recorded on a magnetic tape by the and improved rotation control device for use in an apparatus 75 magnetic tape apparatus shown in FIG. 1;

3 4

FIG. 3 is an exploded perspective view of a part of the drive drum S3 and serves to precisely control the rotating speed of

system for the votary head assembly and the magnetic tape; the shaft 77 of the cotary head drum 53 independently of the

FIGS. 4a to 4d are diagrammatic views showing the relation number of rotations of the synchronous motor 70. The com

between pulleys and a belt in a stepless speed change bination comprising the two conical pulleys 76 and 78, the

mechanism which is the basic component in the device ac- 5 elastic belt 75 and the eddy current brake means 79 is

cording to the present invention; designated in the present invention as a stepless speed change

FIGS. 5, 6 and 7 are diagrammatic views showing other mechanism. The eddy current brake means 79 may, for examforms of the stepless speed change mechanism; and pie, have such a structure that an exciting iron core 82 having

FIG. 8 is a schematic block diagram showing one form of thereon a DC exciting winding 81 surrounds a squirrel-cage

the rotary head drive control system in the device according to 10 induction rotor 80 of the aluminum die casting type which is

the present invention. generally used in an induction motor.

In FIG. 2, there is shown one form of the tape drive system The stepless speed change mechanism which is the basic

in the device according to the present invention which is and essential component of the rotation control device ac

adapted to drive a rotary head assembly in a synchronous rela- cording to the present invention will be described in more

tion with the phase of a reference signal. The drive system is 15 detaj| with reference to a model diagrammatically shown in

mounted on the base plate 51 which is generally called a tape Fjgs. 4a to 4d, wherein FIG. 4a is a front view, FIG. 4b is a

transport panel. A tape guide 52 of cylindrical shape is pro- sectional view along the centerline of the belt and FIGS. 4c

vided with a housing 66 which is securely fixed to the panel and ^ are explanatory front views, respectively, of the

51. The tape guide 52 is provided with a slit (not shown) stepless speed change mechanism.

through which the front end of two magnetic heads 54 and 55 zu It is commonly known that, in case an elastic belt is trained

mounted at diametrically opposite positions on the periphery around two conical pulleys and is thereby driven, the belt runs

of a rotary head drum 53 can protrude from the tape guide 52. along the peripheries of the two pulleys at positions of dif

A magnetic tape 57 fed from a supply reel 58 travels past an ferent heights from each other since tne belt is judged

idler 59 and a guide post 60 to engage the tape guide 52 along toward the ,arge diamcter cnd of each pulley and thus makes a

an arcuate path in such a manner as to partly wrap up the tape certain angle with respect to the horizontai p)ane. h is a|so

guide 52 for receiving a recording thereon or for reproducing known that the beU moves away from the apex of tnc conica|

a ecording therefrom by the action of the magnetic heads 54 Uey having a ,arger cone ang,e when these two pu„eys have

and 55 mounted on the rotary head drum 53. The magnetic cone different from each other.

tape 57 having been recorded or reproduced leaves the tape 3Q Suppose now that conica, pulleys 85 and 86 of the same

guide 52 to be guided past another guide post 61, a control shape havjng a suitable cone angle are mounted in opposite

signal record-reproducing head 62, a capstan means 63 and an directions to each other on two parallel shafts 83 and 84,

!dler 64 to be finally taken up on the takeup reel 65. The respectiveiy, and a flat rubber belt 87 is trained under a suita

supply reel 58, the idler 59 and the gmde post 60 are so b,e ... ... ^ tWQ „ g5 and g6 when ,he ghaft

mounted on the tape transport panel 51 that they have a d.f- 35 g3 fa ... from a drjve SOUfCe g(a ... number

ferent height relative to the height of the takeup reel 65 and Qf rotations «„ the belt 87 can be driven in a balanced state to

the gmde post 61, with the result that the magnetic tape 57 fo„ow g fixed h ... the ... „ depending on

moving past one gmde post 60 toward another guide post 61 the CQne ,e of ^ ... „ g5 and ^ ^ ...

helically runs on the tape guide 52 while making a certain devel d in the belt g7 due to a load t0 jm arted to the

angle with respect to the surface of the tape transport pane 40 ^ g£and ^ force of frictjon deve,0 ed bet4en lhe belt

51. Thas, the recording and reproduct.on of the helical g? and ... ^ pulleys 85 and 86, with the

scanning type can be applied to the magnetic tape 57, and its . ... „ . . r ... , . ., ,

. :? . .• j L j i so i , • J result that a dnving force is transmitted to the shaft 84 to

apparent that magnetized bands 67 and 68 of the kind as , . . , „, „. f . . . e . .■

, . „, _ „ e „ , , , rotate the shaft 84 at a certain number of rotations n.,.

shown in rIG. 2 are formed on the magnetic tape 57 by the . ... .. .. ... , . ., . ., , r

i. J *a J ^c- Mi ■ i . i_ In this connection, it will be apparent that the number of

magnetic heads 54 and 55. It will also be apparent that, when 45 . .. „., , . , „. „. .rr , , ., ... r

0 .. ... „ .. ,„ . i, rotations of the driven shaft 84 is reduced as the position of

the mounting positions of the guide posts 60 and 61 are ., , ,. „_ ,. , ... ■ r-i^

.. ,, , j , _ . , the belt 87 moves in a direction as shown by the arrow in FIG.

suitably selected, the range of engagement between each mag- . ,, , .... ..... ... .

.. . , ..■ . . , •. .. . . 4a. Under the state m which the position of the running belt 87

netic head and the magnetic tape can be limited to a substan- .... . . .... , , , • , ,

.... . . „ °. , .... . .■ is stabilized as described above, the number of rotations of the

tially semicircumferential range through which each magnetic . . . . „. , ... , • , . .,

u j . . .... . . ... . D ... . c „. driven shaft 84 can be varied by applying a torque load to the

head rotates m sliding contact with the tape. By this type of ar- 50 , - „. , , j, L 7

rangement one of the magnetic heads starts to engage the shaft 84 mfuns such ^ an eddy current brake means. The

magnetic tape 57 when the other is about to leave the mag- TMpartation of the torque load to the driven shaft 84 causes a

netic tape 57. In FIG. 2, the reference numeral 69 designates a va"atl°" ln the te"s,°n °f,the, beltu87,10 ... sh,ft ,he

magnetized band formed by the stationary head 62. balanced position of the belt 87 in the d.rection of the arrow

FIG. 3 illustrates in an exploded perspective fashion a 55 so that the number of rotations of the dnven shaft 84 can be

system for driving the magnetic tape and the rotary head as- varied without varying the number of rotations of the driving

sembly in the magnetic tape apparatus having the rotation snattoj.

control device embodying the present invention. An AC The above situation will be described in further detail with

synchronous motor 70 adapted to be driven by a commercial reference to FIGS. 46, 4c and 4d. FIG. 4b is a cross-sectional

power supply is supported on the panel 51. A pulley 100 is 60 view to show the engagement between the belt 87 and the pul

mounted on one end of the shaft 71 of the motor 70, and a leys 85 and 86 when viewed from the top ends of the shafts 83

torque-transmitting elastic belt 73 is trained around the pulley and M Suppose now that the pulleys 85 and 86 rotate in a

100 and a pulley 72 which serves both as a speed reducing direction as shown by the arrow depicted in each of them, and

means and a flywheel so as to drive a tape-driving capstan T< and T„ designate the belt tension on the tensile side on the shaft 74 connected to the pulley 72 in a manner well known in 65 slack side, respectively, relative to each of the pulleys 85 and

the art. Thus, the capstan shaft 74 has its drive power supplied 86 under the running state of the belt 87. Then, there is a rela

from the synchronous motor 70 to thereby rotate at a constant ti°n T, > T, between these tensions. On the other hand, the

number of rotations. position at which the belt 87 engages the surface of each coni

On the other hand, a second elastic belt 75 is trained around cal pulley is primarily determined by the point at which the a conical pulley 76 fixedly mounted on the other end of the 70 belt 87 starts to engage the pulley. Therefore, the belt 87 at

shaft 71 of the synchronous motor 70 and a conical pulley 78 the entrance to the conical pulley 86 mounted on the driven

fixedly mounted on the shaft 77 of the rotary head drum 53, so shaft 84 is stabilized at a position at which an axial component

that the shaft 77 can be driven by the synchronous motor 70 /s of the belt tension T, is balanced with an axial components

through the second belt 75. An eddy current brake means 79 F, of the friction force of the conical pulley 86 as shown in is operativeiy associated with the shaft 77 of the rotary head 75 FIG. 4c. Accordingly, as the load torque imparted to the

be turned into a pulse signal at 30 cycles per second which is 35 starts to disengage the magnetic tape lie in the vertical blankthen suitably delayed and shifted in its phase by a phase shifter ing period of the television signal. In this respect, it will be un93. The signal is then passed through a switch St to be supplied derstood that the period of the vertical synchronizing signal as one of the input signals to a phase comparator 94. On the which is one-sixtieth of a second is equal to the time corother hand, a permanent magnet 101 is fixedly mounted at a responding to each individual tracing section of the tracks 67 suitable position on the peripheral portion of the rotary head 40 and 68 drawn by the magnetic heads 54 and 55 on the magdrum 53 in such a relation that it is closely opposite to a sta- netic tape, and further the rotation of the head drum 53 carrytionary pickup head 102 so that a signal is derived from the ing thereon the magnetic heads is so controlled as to be in pickup head 102 by each rotation of the rotary head drum 53. synchronism with the phase of the vertical synchronizing The above signal constitutes another input signal to the phase signal. Therefore, by preliminarily selecting a suitable value comparator 94. The phase comparator 94 compares the 45 for the delay time of the phase shifter 93, it is possible to set

from a commercial power supply, respectively, and the torque 55 drum 53 carrying thereon the magnetic heads 54 and 55 is

second is compared in the phase comparator 94 with the 65 with the rotation control device according to the present inphase of the signal at a frequency in the vicinity of 30 cycles vention has a tape drive system and a rotary head drum drive per second which is derived by the pickup head 102 in system which are remarkable simplified, inexpensive and easy response to each rotation of the head drum 53 rotating at a to maintain compared with like systems in the prior magnetic speed in the vicinity of 1,800 r.p.m. An error signal derived by recording and reproducing apparatus described previously, the phase comparison between these two signals is smoothed 70 More precisely, in contrast to the prior form in which the cap

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