| 摘要 |
1,204,618. Automatic speed control. PHILIPS ELECTRONIC & ASSOCIATED INDUSTRIES Ltd. April 24, 1968 [April 26, 1967], No.19414/68. Heading G3R. A motor 2 drives an apertured disc 4 cooperating with a lamp 6 and photo-cell 7 to produce a pulse for each revolution of the disc, a train of these pulses forming a control signal 8 representing the speed of the motor. An eddy-current brake 10 is fed through amplifier 11 with a regulating signal 12 derived from a bi-stable multi-vibrator 13 which passes to a first stable state by the control signal 8, and to a second state by pulses of a reference signal 14. When the system is synchronized the two signals have the same frequency, each reference pulse being followed by a control pulse. A short time before a reference pulse is received, stage A of multi-vibrator 23 is blocked, its stage B being conducting. Gate 21 is closed, gate 22 is open, and a monstable multi-vibrator 19 is in its stable state so that gates 17, 18 are open, the multi-vibrator 13 being in its first stable state. When a reference pulse is received, the multivibrator 19 does not change state, and the gates 17, 18, remain open. The reference pulse is passed through gate 17 to the multi-vibrator 13 which passes to its second state. The multivibrator 23 changes state whereby gate 22 is closed and gate 21 is opened. When the next pulse of the signal 8 is received, the multi-vibrator 19 does not change state and the gates 17, 18, remain open. The pulse passes through the gate 18 to the multi-vibrator 13 which passes to its first state, the stage B of the multi-vibrator 23 becoming conductive so that gate 21 is closed and gate 22 is opened. In this manner, the multivibrator 13 delivers the pulse train 12 for controlling the brake. When the system is being started, a number of pulses of the reference signal occur between successive pulses of the signal 8. In these circumstances, the multi-vibrator 13 does not change its state continually but remains in a single state for a period dependent upon the time constant of the multi-vibrator 19. The motor is thus given time to be brought into synchronizm. In another arrangement, the multi-vibrator 23 and the gates are not connected directly to the leads for the reference and control signals, but to the ouputs of the gates 17, 18, Fig. 3 (not shown). In a further embodiment, the multi-vibrators 13, 23, are combined to form a signal bi-stable multivibrator, Fig.4 (not shown). |
