Patent GB-1036235-A (GB)
Title: Improvements in or relating to tape drive systems
IPC: H02P7/285
Filed: 1964-05-15
Abstract: 1,036,235. Automatic speed control. AMPEX CORPORATION. May 15, 1964 [Sept. 6, 1963], No. 20298/64. Heading G3R. [Also in Division H3] A magnetic tape 15 is driven in either direction between reels 13 by a non-slip capstan motor 44 having low armature inertia. Forward-reverse and on-off signals are applied to a command signal source 49 from a data processing system, a ramp generator 50 producing positive or negative signals having an amplitude representing the desired motor speed during acceleration, deceleration, and constant-speed periods of operation of the motor. These signals are applied through resistor 51 to D.C. amplifier 47, a tachometer generator 46 providing a feedback signal through resistor 52. The input command signal from the source 49 has a stepped waveform, whereas the ramp signal has a constant-slope leading edge which thereafter has a uniform level and a constant-slope lagging edge. The lengths of tape-loops within vacuum chambers 21, 22 are maintained between predetermined limits by means of differential-pressure switches controlling reel motors 27, 28. In another arrangement, the speed-sensing device is formed by a graded disc and photo-cell system providing an alternating signal whose frequency is proportional to speed, and which is converted to a D.C. signal whose magnitude represents the speed. The alternating speed-signal may be phase-locked with a reference signal after the nominal velocity has been reached. Alternatively, the ramp speed control signal is used to vary the frequency of an oscillator in the range between nominal and zero velocity, while the signal from the graded disc is phase-locked therewith for fine speed control during acceleration and deceleration intervals. The tape may be advanced in a step-by-step manner, the start and stop distances being equal. The start-stop commands are applied to ramp generator 50 to control the recording and reproducing of data on tape 15. For recording, a "write" mode signal is applied to AND gate 90, the trailing edge of the command pulse being detected by differentiator 91 and passed through diode 92 to enable gate 93 which transfers data to head 94. The leading edge of the command pulse acts as a release signal to the data source. The reproducing mode is initiated by enabling AND gate 95, the incremental tape motion beginning with a command signal, and the frame of digital data detected by the head assembly being subsequently fed through amplifier 96 to detector 97. The first output signal from the detector is passed by OR gate 98 to multivibrator 99, producing a strobe pulse. This passes gate 95 to gate 101 which passes the frame of digital data. The strobe pulse is also used to terminate the incremental step. The ramp generator comprises a transistor amplifier input stage providing a constant control signal for charging a capacitor which is coupled to an output stage. This stage has an output proportional to the charge on the capacitor but of opposite polarity to the command signal. Negative feedback gradually reduces the input to the transistor amplifier to zero thereby preventing further charging of the capacitor, Fig. 3 (not shown).