Patent GB-1335889-A (GB)
Title: Programmable transport controller
IPC: G11B27/32
Filed: 1971-11-12
Abstract: 1335889 Automatic speed control AMPEX CORP 12 Nov 1971 [16 Nov 1970] 52756/71 Heading G3R A record medium has sequentially addressed storage locations and is driven at a controlled speed to position a given location at a transducer. The address signals are detected to provide speed and distance indications, and the medium is driven at discrete command speeds which are determined by the distance from the desired storage location. In the system shown, video tape 11 is driven reversibly by motors 27, 28 past a magnetic head 31 which picks up address and timing signals 23 and feeds them to an address decoder 33. A first output signifying the direction of actual tape movement is fed on line 147 to a drive amplifier 29. A second output comprising pulses at a frequency proportional to tape speed is supplied to a counter 66, and a third output indicating the tape position is fed to a unit 34 for comparison with a required location address 38. An output from unit 34 on line 35 informs the amplifier 29 of the direction of the required tape movement, and a further output on line 114 stops the drive when the desired location is reached. A bus connector 43 supplies the digital difference in actual and required addresses to a selector 42 which produces an output on'one of lines 47-56 depending on which of a number of ranges the difference signal falls within. If the signal corresponds to a tape distance greater than, say, 600 inches, line 47 is energized, causing the tape to be driven at maximum speed without control. If the distance is less than 600 inches, one of the other output lines is energized to set a predetermined count into the counter 66. Thus, pulses from the decoder 33 must fill the remainder of the counter before a monostable multivibrator 86 produces an output pulse. The arrangement thus acts as a frequency divider, in which the divisor is decreased in successive steps as the distance to the required location is reduced. The multivibrator output is fed on line 76 to a circuit 41 for phase comparison with a fixed reference pulse signal from a circuit 139, so that the successive changes in signal division have the same effect as a system in which the reference pulse frequency is successively decreased. Such a system may alternatively be used. The output from comparator 41 causes the amplifier 29 to drive one or other of the reel motors 27, 28 selectively so that the tape is accelerated and decelerated in a controlled manner until the required tape storage location is positioned at the head 31. The unit 34 has a switch 36 to permit operation with tape having 25 or 30 TV frame signals per second. The selector 42 may be adjusted to operate with tape transports having different deceleration characteristics by setting a switch 44 which determines the distance settings corresponding to the ranges represented by output lines 47-56. A switch 46 is provided to adapt the selector for use with tapes having different length storage locations. The reference pulse generator 139 has switches 126, 128 which enable pulse frequencies of 900 Hz or 450 Hz to be produced, and a switch 131 may also be closed to reduce the frequency by 20%. The arrangement of logic gates in the amplifier 29, Fig. 6 (not shown), and various speed/distance trajectories, Figs. 2-5 (not shown), are also described.