US3586259A

US3586259A - Drive assembly for magnetic tape recorder

Info

Publication number: US3586259A
Application number: US839181A
Authority: US
Inventors: Hubert Richt
Original assignee: Suddeutsche Mechanische Werkstatten Wolf Freiherr Von Hornstein KG
Current assignee: Suddeutsche Mechanische Werkstatten Wolf Freiherr Von Hornstein KG
Priority date: 1968-04-26
Filing date: 1969-07-07
Publication date: 1971-06-22
Anticipated expiration: 1988-06-22
Also published as: GB1230303A; FR2045059A5; DE1774179A1

Abstract

In a drive assembly for magnetic tape recorder a separate motor is associated with each of the reels. The motors are reversible so that the tape can be driven bidirectionally. An automatic control system maintains the constancy of the tape motion at any speed by monitoring the actual tape speed and comparing it with the nominal value thereof. Upon detection of a difference between the two data a servo loop is actuated to correct the deviation of the actual from the nominal speed. Adequate tension of the tape is maintained at all times.

Description

- United States Patent- [72] Inventor Hubert Richt [56] References Cited swung Germ"! UNlTED STATES PATENTS P 839d 3,045,937 7/1962 Johnson 242/203 PM My 3 104 071 9/1963 N b 242 ew erg /203 [451 3 141 626 7/1964 Hoskin 242/203 [73] Assignec Suddeutsche Mechanische Werkstatten Wolf Freiherr von Hornstein KG Primary Examiner-Leonard D. Christian Barmseestr. ll, Munich, Germany Attorney-Nolte and Nolte ABSTRACT: In a drive assembly for magnetic tape recorder a [54] DRIVE ASSEMBLY FOR MAGNETIC TAPE separate motor is associated with each of the reels. The mo- RECORDER tors are reversible so that the tape can be driven gchjmszmawmg Figs bidirectionally. An automatic control system maintains the [52] US. Cl 242/203, constancy of the tape motion at any speed by monitoring the 242/208. 318/7 actual tape speed and comparing it with the nominal value [51] Int. Cl 81 lb [5/32, thereof. Upon detection of a difference between the two data G03 b 1/04 a servo loop is actuated to correct the deviation of the actual [50] Field of Search 242/201, from the nominal speed. Adequate tension of the tape is maintained at all times.

PATENTED JUN22 |97| wsxr P/a/T INVENTOR ATTORNEYS DRIVE ASSEMBLY FOR MAGNETIC TAPE RECORDER BACKGROUND OF THE INVENTION In prior drive assemblies for magnetic tape'recorders comprising a single motor, the fly wheels and also the capstan, are driven through one gearing, and the coupling of the takeup reel is driven through another gearing or through the fly wheels, The tape is advanced by the capstan rotating at constant angular speed and is wound upon a spool supported by the takeup coupling. For high-speed winding, respectively unwinding of the tape one of reel couplings is driven at increased velocity while the other one is braked. Simultaneously, the friction contact between the capstan and the tape is suspended by releasing the free-running pressure roller from the tape.

An assembly of this type requires a large number of mechanical structural elements for the various tape runs, for example, for standard speed, for high speed and for the stop command. The high velocity of components such as the driving motor and the friction pulleys generate vibrations and background noise. Another drawback is the need for rubber driving belts and rubber contact surfaces for the friction pulleys which are subject to deterioration by dirt or wear, and to deformation. Furthermore, the sliding release couplings are liable to slip during operation of the assembly, while also causes interfering noise and deterioration of the friction surfaces. In an assembly in which the tape is driven by a capstan cooperating with a pressure roller it is impossible to avoid a certain amount of tape slippage relative to the capstan. The slippage is nonlinear because of inhomogeneities in the rubber pressure roller, which are introduced during the manufacturing process, and results in fluctuations of the sound pitch and in drift of the tape speed. A further disadvantages of singlemotor assemblies isthat it is necessary, for remote control, to actuate not only the gearing and the brakes for the reel couplings but the pressure roller, so that additional expensive electromagnetic actuating elements, such as for example, solenoids, must be provided.

Another conventional drive mechanism comprises a separate motor for each of the reels, as well as a driving motor rotating at constant speed. The shaft of the motor forms the capstan, so that friction gearing, pulleys and driving belts are eliminated. Remote control of a three-motor assembly is simpler than control of a single-motor system because of the reduction in the number of structural mechanical elements. The tape can be driven bidirectionally by reversing the rotational direction of the motors. However, since the driving motor has a high rotational energy, there is a substantial dead time after reversing the direction of rotation, until the desired speed in the opposite direction is attained.

Although three-motor assemblies, with a lesser number of mechanical structural elements, are more reliable in operation than single-motor assemblies, they are considerably more expensive because they require high quality and costly motors. The demands on the driving motors are particularly strict with regard to quietness and steadiness of operation. The other components, for example, the capstan and the pressure roller must be high-precision parts. Since the tape is advanced, as in single-motor drives, between the capstan and the pressure roller, a certain amount of tape slippage is unavoidable. The risk of slippage is even greater in a three-motor system because the driving motor is operated at relatively high speed, so that a capstan ofsmall diameter is required to drive the tape at the proper speed. As in singlemotor systems with remote controls, means must be provided to actuate the pressure roller electromagnetically which adds to the expenses for the assembly.

In yet another known mechanism the drive capstan for the tape is dispensed with, and a DC motor is provided for the takeup reel coupling only. One end of the motor shaft is frictionally engaged with a friction surface provided at the circumference of the lower part of the reel coupling. The rotational speed of the motor is regulated by a DC generator whose rotor is driven by the tape, so that the tape speed is kept constant. The advantage of the mechanism which has neither a capstan nor fly wheels or a pressure roller, is offset by the noise produced by the high-speed driving motor. The vibrations of the motor and of the contact surface on the lower part of the reel coupling, which is made of rubber, and the abrasion, contamination and deformation of this surface all affect the synchronization of operations in a way which cannot be compensated for. If the motor shaft remains in contact with the surface of the reel coupling when the mechanism is stopped, deformations such as dents are likely to be produced therein, which ultimately affect the symmetry of the coupling. A similar skewed alignment may result from the deposition of dust or abrasion particles on the contact surfaces.

Another drawback is that the motor must be pivotably mounted so that the shaft can be rapidly and selectively thrown into gear with either of the two reel couplings for highspeed rewind operations.

SUMMARY OF THE INVENTION It is an object of the present invention to overcome the disadvantages of known drive assemblies for magnetic tape recorders by providing a simple and economical assembly adapted for bidirectional operation.

Another object of the present application is to provide an improved assembly substantially without mechanical structural elements and high-precision components.

A further object of the present invention is to provide an assembly which is reliable in operation, responsive to commands, and adapted to maintain constant velocities.

These objects and others which will become apparent hereinafter are attained, in accordance with the present invention, through a pair of reel motors coaxial with the spool supports, respectively the couplings of each of the two reels. Preferably, motors of the deep-bar, squirrel cage motor type may be used. During operation of the assembly, the rotational speed of one of the motors is regulated by a servo loop so that the speed of the tape is kept constant for at least one selected tape velocity. The actual speed of the tape is read off, as is well known, from markings provided on a roller which is turned by the motion of the tape, and which may be scanned inductively, capacitively, galvanically or optically. For example, if the markings are serrations made in a ferromagnetic surface and scanned by a polarized magnetic head, the frequency of the alternating current derived therefrom is proportional to the actual tape velocity. The frequency is compared with a reference frequency representing the nominal value. A differential between the two valves which is equivalent to the instant deviation of the tape velocity from the desired value is fed as a signal to a variable gain amplifier which excites the driving motors for example, through an intermediate element. If the actual tape velocity is too high, or too low, the amplifier causes driving current to be fed to the windings of the respective motor proportional to the correction required to counteract the deviation. Simultaneously, the opposite motor is energized to drive at a speed and in a direction which maintains adequate tape tension.

It is also possible to regulate the tape speed by controlling for example, the speed of the payoff reel motor by the means described above while the motor of the takeup reel is driven without controls.

When the desired velocity of the tape is to be changed for recording or reproduction, a different nominal value corresponding to each of the speeds is used as a reference, so that the tape speed can be kept constant by comparison therewith.

The driving motors for the reels, according to a preferred embodiment of the above invention, are of the type having a constant torque which is independent of the position of the rotor and sufficient to overcome the inertia of the spool supports, respectively of the reel couplings. Suitable motors are, for example, DC or induction motors with an adequate number of poles, or DC or induction motors whose velocity,

respectively torque, can be conveniently regulated. Of particular advantage are deep-bar squirrel cage rotor-type motors whose torque is independent of the rotor position and which have a relatively high torque to low inertia ratio.

The use of two-reel motors driven at low speeds eliminates, to a very large extent, motor vibrations which affect the desired steadiness of the tape run. lrregularities in the motor drives and the sliding noise of the reel couplings are also avoided. The rotational energy of the drive mechanism components is relatively low, so that a fast switching to another tape velocity, or reversal of the tape drive direction, does not subject the tape to a large tension impulse.

According to a preferred embodiment of the invention the reel couplings are mounted on the rotors of the reel motors, so that jerky impacts on the tape during a reversal of direction, or following the stop command, can be avoided. The couplings have the dual purpose of acting as arresting brakes.

In a preferred embodiment the constancy of the tape speed is maintained even for high-speed runs, which makes it easy to locate a desired-position on the tape. A constant coefficient coordinates the high-speed run with each of the standard tape velocities, so that high-speed operation requires a constant fraction of the recording time, independent of the tape velocity during the recording operation. This is particularly advantageous for finding a particular place on the tape since the temporal relation of individual recording positions is preserved.

The drive assembly, according to the present invention, comprises a single servosystem for both reversible motors to control the tape speed, and a single voltage source for producing opposite torques which can be switched over when the direction of the tape transport is to be changed. I

The coaxial arrangement of the motors and i the real couplings makes it possible to drive the tape in both directions. The change from one direction to the other can be achieved simply and economically by switching the control system for the regulation of the tape speed and the voltage source for the production of the torque, from one motor to the other. In either direction of motion of the tape the standard velocities and high-speed operation can be regulated through feedback of the actual values and comparison with the nominal values corresponding to the desired speeds.

A further characteristic of the invention is that an additional marking is provided on the roller driven by the tape. The marking which may be scanned by inductive, capacitive galvanic or optical detection instruments serves to measure the tape length. According to a preferred embodiment of the invention, the marking is a line which is scanned photoelectrically and transmitted as a signal to a suitable counter.

The roller, which is partially encircled by the tape, moves easily and is adapted to steady the tape by damping the longitudinal oscillations thereof. According to a preferred em bodiment the roller is provided with tape guides, so that additional guides, for example, guide bolts, are not required.

The distinctive features of the present invention lie in the almost complete absence of mechanical structural elements, of high precision parts, of special gearing, particularly of gearing including rubber components such as friction pulleys or belts, and of high-speed elements. In operation, the assembly is extremely quiet, reliable and economical. It responds fully to remote controls and can be equivalently operated in both directions.

The above and other objects, features and advantages of the present invention will become more readily apparent from the following description, reference being made to the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a fragmentary front elevational view of a drive assembly according to the present invention; and

FIG. 2 is a somewhat diagrammatic plan view of the drive assembly shown in FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIG. 1 there is shown a pair of

motors

1 and 2 of the external rotor type, preferably of the deep-bar squirrel cage rotor type. The mounting of such motors in the frame of a magnetic tape recorder is well known to those skilled in the art and requires no further explanation. A pair of

couplings

5 and 6 connect the

rotors

3 and 4 of the motors l and 2 with a pair of spool supports 22 and 23 for the reels 7 and 8 which are supported thereon in coaxial alignment with the motors.

At any one time one of the reels 7 and 8 serves as the payout reel and the other one as the takeup reel. A tape 9 extends between the reels 7 and 8 and is adapted to be wound upon the takeup reel and simultaneously unwound from the payout reel upon energization of the respective motors. The path of the tape 9 between the reels 7 and 8 leads past the erasing heads L and L as well as past a magnetic head assembly K therebetween which is coupled to recording and reproducing circuits (not shown). On its path between the reels 7 and 8, the tape 9 also passes over

rollers

10 and 11, the latter being rotatably attached to the frame or housing of the instrument and symmetrically positioned intermediate the reels. The rollers l0 and 11 are guides for the tape 9 and are rotated when the tape is moved over and engages them, so that their angular velocity is proportional to the linear velocity of the tape. Markings 19 are provided on the circumference of the roller 11 from which the velocity of the tape motion can be obtained by suitable scanning means, such as M. Markings 21 shows as line markings applied to the circumference of the roller 10 are adapted to be read by a photoelectric scanner P to determine the length of the tape transported between the reels 7 and 8, respectively wound upon one of these reels.

In the illustration of FIG. 1 the drive assembly is in the Go position, wherein the locking

elements

12 and 13 which are pivotally mounted at 24 and 25 inthe frame of the instrument, are withdrawn from engagement with the

rotors

3 and 4 of the motors l and 2. The electromagnetic release, of the

elements

12 and 13 from the

rotors

3 and 4 is actuated by closing the switch S (FIG. 2), thus causing current to flow from a power source 15 to the solenoid l4. Excitation of the solenoid 14 attracts the armature 16 against the force of spring 17 to which it is attached. The

elements

12 and 13 which are symmetrically and pivotally attached at one of their ends to the armature 16, are displaced from their locking position when the armature is drawn toward the interior of the solenoid 14, thus releasing the

rotors

3 and 4. If the excitation of the solenoid 14 is interrupted, for example upon the stoP" command, or upon disconnection of the drive assembly and switching off of the

motors

1 and 2, the armature 16 is pulled out of the solenoid 14 by the force of the spring means 17, so that the locking

elements

12 and 13 are again moved toward the

rotors

3 and 4. In this way the rotor of the motor associated with the payout reel is firmly held by one of the locking

elements

12 and 13 whereas the rotor of .the motor associated with the takeup reel is only lightly braked. For example, if the tape 9 is transported in the direction of the arrow 18 the rotor 3 is instantly locked by the locking element 12 whereas the rotor 4 is only lightly braked. The tension of the tape 9 is regulated essentially by the locking momentum of the coupling on the payout reel, that is, in the present example by the coupling 5, so that slack loops of tape are prevented.

The speed of the tape 9 is controlled by comparing the actual speed with the nominal speed assigned to the respective tape drive velocity and by correcting any deviation therefrom. For this purpose the actual speed is continuously checked by scanning the markings 19 applied to the circumference of the roller 11. The markings 19 which may be serrations made from ferromagnetic material pass in front of a scanner such as a polarized magnetic head M which is connected to a suitable electric circuit. As the roller 11 is rotated by the motion of the tape 9 trained over it, a current is produced in the circuit whose frequency is proportional to the instant speed of the tape. Fed as a signal into the comparison element V, the respective frequency is matched against a nominal value 0 stored therein. Any difference between the actual value and the nominal value is transmitted as another signal to a variable gain amplifier R which regulates the speed of the motor 2 through an appropriate correcting element (not shown). If the instant tape speed is slower than the nominal value, the described automatic control system causes motor 2 to be excited until the desired tape speed is produced. Corresponding corrections are made if the instant tape speed is too fast. If the speed of the tape 9 is too slow, that is, if motor 2 is temporarily driven with increased excitation, a voltage lower than the nominal voltage is fed from the source Sp to the motor 1 to produce a counter torque which is adequate to maintain tension in the tape for the winding process and for contact with the heads L,, K and L The actual tape speed readout from the markings 19 on the roller 11 at different standard type velocities and during highspeed winding, respectively rewinding operation, can be matched against nominal values corresponding to the respective velocities and stored in the appropriate memory positions of the servoloop. in this way, the automatic control system can immediately correct any deviation of the actual speed from the nominal speed for different tape velocities.

In a likewise manner it is possible to switch the motor 1 on the payout reel 7 to automatic control for maintaining a constant speed, while motor 2 which drives the take up reel 8 is supplied directly with the rated voltage from the source Sp. The shifting from one system to the other is easily accomplished by disconnecting the terminals e-f and b-c in the flow diagram and by connecting the terminals d--f and ac instead.

The assembly, including the tape, is equivalently operable in either direction, that is in the direction indicated by the arrow 18 or in the direction'of the arrow 20. in order to drive the tape at controlled speed in the direction of arrow 20 it is only necessary to switch the motor 2 which is, in this case, coordinated with the payout reel to automatic control and supply the motor 1 coordinated with the takeup reel with thenominal voltage from the source Sp. Alternately the takeup reel motor 1 may be switched to automatic control, and the payout reel motor 2 may besupplied with less than the rated voltage from the source Sp to develop a counter torque so that adequate tension of the tape 9 can be maintained. For the latter arrangement it is necessary to connect the terminals ac and df.

Through the above-described automatic control means it is possible to keep the tape speed constant in either direction of transport and at all standard velocities as well as at high-speed operation.

What I claim is:

l. A drive assembly for a magnetic tape recorder comprising a pair of motors each having a drive shaft, a power source for driving said motors, means for selectively driving said drive shaft at different speeds, means for regulating the speed of either of said drive shafts, reversing switch means for changing the direction of motion of said drive shafts, a reel operatively connected with each of said drive shafts and rotatable therewith, a tape wound on and extending between said reels, means for winding said tape upon one of said reels at a predetermined speed and simultaneously unwinding said tape from the other of said reels, means for measuring the actual speed of said tape advanced by said reels, means for converting said measurements into signals, means for correlating said signals with stored signals representative of the nominal speed corresponding to at least one of said predetermined tape speeds, and an automatic control system for correcting drift of the actual tape speed relative to the nominal tape speed whereby constancy of motion of said tape is obtained.

2. A drive assembly as defined in claim 1 wherein said motors are external rotor-type motors.

3. A drive assembly as defined in 'claim2 wherein said motors are deep-bar squirrel cage rotor-type motors.

4. A drive assembly as defined in claim 2 comprising a spool support for each of said reels and a coupling coaxially mounted on each of said motor rotors connecting said motors and said spool supports.

5. A drive assembly as defined in claim 1 wherein said speed measuring means comprise at least one roller rotating at an angular speed proportional to the linear speed of said tape, at least one marking applied to the circumference of said roller, and a counter registering the number of revolutionsof said roller per unit of time.

6. A drive assembly as defined in claim 5 wherein said marking is a serration formed from ferromagnetic material and said registering counter comprises a polarized magnet proximate to said roller having said marking.

7. A drive assembly as defined in claim 5 wherein said marking is a line and said registering counter comprises a photoelectric cell.

8. A drive assembly as defined in claim 7 comprising means for correlating the number of revolutions of said roller with a number representative of the length of the tape.

9. A drive assembly as defined in claim 1 comprising a single automatic control system for regulating the speed of said motorin either direction of motion, a single voltage source for producing a counter torque in either of said motors, means connecting said automatic control system and said voltage source with either of said motors, and means for switching said automatic control system and said voltage source from one of said motors to the other of said motors during a reversal of the direction of motion of said motors.

Claims

1. A drive assembly for a magnetic tape recorder comprising a pair of motors each having a drive shaft, a power source for driving said motors, means for selectively driving said drive shaft at different speeds, means for regulating the speed of either of said drive shafts, reversing switch means for changing the direction of motion of said drive shafts, a reel operatively connected with each of said drive shafts and rotatable therewith, a tape wound on and extending between said reels, means for winding said tape upon one of said reels at a predetermined speed and simultaneously unwinding said tape from the other of said reels, means for measuring the actual speed of said tape advanced by said reels, means for converting said measurements into signals, means for correlating said signals with stored signals representative of the nominal speed corresponding to at least one of said predetermined tape speeds, and an automatic control system for correcting drift of the actual tape speed relative to the nominal tape speed whereby constancy of motion of said tape is obtained.

3. A drive assembly as defined in claim 2 wherein said motors are deep-bar squirrel cage rotor-type motors.

5. A drive assembly as defined in claim 1 wherein said speed measuring means comprise at least one roller rotating at an angular speed proportional to the linear speed of said tape, at least one marking applied to the circumference of said roller, and a counter registering the number of revolutions of said roller per unit of time.

9. A drive assembly as defined in claim 1 comprising a single automatic control system for regulating the speed of said motor in either direction of motion, a single voltage source for producing a counter torque in either of said motors, means connecting said automatic control system and said voltage source with either of said motors, and means for switching said automatic control system and said voltage source from one of said motors to the other of said motors during a reversal of the direction of motion of said motors.