| 摘要 |
1, 084, 840. Automatic speed control. CONTINENTAL OIL CO. June 29, 1965 [Aug. 24, 1964], No. 27547/65. Heading G3R. A D. C. motor 20 driving magnetic tape drum 22 has its speed selected by switch 28, a photoelectric chopper 24 delivering a feedback signal whose frequency indicates the actual speed of the motor. A reference oscillator 150 is associated with multi-vibrator 154 providing outputs A, B, of opposite phase which are further divided to provide reference frequency outputs C, D, phasedisplaced by ninety degrees. The motor feedback frequency on line 90 has a fixed value when the motor is correctly following the set speed, no matter where the switch 28 is positioned. Changes of frequency of the signal on line 90 are indicated by variations in the spacing of square wave pulses derived from multi-vibrator 96, these pulses being filtered to afford a D. C. signal on line 92 representing the actual motor speed. A phase detector 102 compares the signals on lines 90, 107, to derive a D. C. signal on line 94 having an amplitude indicating the phase difference and a polarity indicating the direction of the phase-shift. The reference frequency signal on line 142 is fed to converter 36 providing a D. C. signal on line 148 proportional to the desired motor speed. The signals on lines 92, 94, 148, are applied to summation networks 166, 168, connected to differential amplifier 170, a further feedback signal being taken from the output of this amplifier and applied through capacitor 228 and one of the attenuation resistors 230-233 to the network 168. This further feedback signal consists of sampling A. C. variations in the output of amplifier 170 and is fed back to the input degeneratively. The velocity-reference and phase-feedback signals are summed in network 166 and the summed voltage is applied to one input of the differential amplifier; likewise, the velocity-feedback and amplifierfeedback signals are summed in network 168 and the resultant voltage is applied to a second input of the amplifier. The output of the amplifier 170 is a direct voltage which is amplified by power amplifier 40 to drive the motor 20. In the event of a sufficient overspeed condition, the control voltage on lead 238 becomes positive and the power amplifier is switched to provide a reverse braking voltage for the motor. A protective circuit 41 is responsive to the motor feedback frequency signal on lead 290 to open contacts 294 when the speed is double its normal value. The motor remains de-energized until a reset switch is opened. |
