| 摘要 |
1,157,362. Automatic speed control. RADIO CORPORATION OF AMERICA. July 29, 1966 [Aug. 20, 1965], No.34292/66. Heading G3R. To drive a magnetic tape forwardly, command source output 18 is changed to a lower voltage level, network 30 providing a signal through temperature-sensitive network 40 to error detector 50. Amplifier 60 operates in a non-linear range to provide a substantially constant overdrive signal to capstan motor 13. As the motor accelerates in the forward direction, tachometer 65 develops a feedback signal. When the output 18 changes to the low level, gate 180 responds to open switch 87 and to close switch 85 whereby circuit 70 filters the ripple component from the velocity signal with a minimum time delay resulting in only a slight phase lag of the velocity signal. As the error signal decreases, the amplifier 60 is operated in a linear range. To accelerate the tape in the reverse direction, the output 19 is changed to a lower voltage level, the network 30 providing a reverse signal, and the switches 85, 87, being respectively closed and opened. During the rewinding operation, the network 30 responds to changes in level of both outputs 19, 20, to provide a larger signal and drive the motor at higher speed. The filter 70 is also connected in the feedback circuit for this operation. When the motor decelerates to the rest condition, the drive signal from the network 30 becomes zero, the error signal assisting in turning the motor off and the amplifier 60 operating first in a non-linear range, then in a linear range, and finally in its dead zone as the error signal decreases. When a turn-off command is received all the outputs 18, 19, 20, are at the higher of two digital levels so that the output of gate 180 is at a lower level. Switches 85, 87, open and close respectively whereby lag network 80 is operative to delay the feedback signal and prevent it from decreasing rapidly. A flip-flop 91 responds to changes in digital signal level of output 18 to close switch 93 so that capacitor 90 is connected in parallel with network 80. This connection increases the time constant of the feedback circuit during the return to zero speed from rotation in the forward direction, thus allowing for the different loadings on the motor during turn-off operations in opposite directions. The system is adapted for reversal of rotation, the filter 70 being included in the feedback circuit so that the dead band of the amplifier 60 is passed through quickly. The network 30 may comprise a voltage divider connected to two constant-current devices and having tappings earthed through electronic switches which are individually controlled by the signals on lines 18, 19, 20. The output on line 33 is taken from a central tapping of the divider. The filter 70 includes a transistor arrangement for minimizing the effective resistance of a charging circuit of a capacitor, the temperature-sensitive network 40 having an identical transistor arrangement. |
