Patent GB-752986-A (GB)
Title: Electrical control of to-and-fro motion of heavy bodies
IPC: G01S1/02
Filed: 1954-08-25
Abstract: 752,986. Control of motors. SPERRY CORPORATION. Aug. 25, 1954 [Sept. 10, 1953], No 24778/54. Class 38(3) [Also in Group XL(c)] An electric motor driving a radar scanner is continuously reversed between predetermined limits by means of a system comprising a velocity signal generator and a positional signal generator which respectively produce electrical signals proportional to the velocity of the driven object at any given time and the position of the driven object with regard to the nearest limit of its desired movement. The two electrical signals are supplied to a comparison circuit wherein a determinable ratio of the positional signal and velocity signal causes an actuating signal to be transmitted to means for braking the driving motor whereby the driven object is stopped in the desired position under various conditions of load, speed, or range of movement. As shown, the alternating- current positional signal is received into the comparison circuit through a transformer 10 from which it passes through resistor 11 and rectifier 12, a resistor 14 and capacitor 15 being provided to smooth the rectified positional signal. The alternating-current velocity signal is applied through a rectifier 16 and is smoothed by the circuit elements 18, 19. When the amplitude of the rectified velocity signal exceeds that of the rectified positional signal, the primary winding of a magnetic amplifier 20 is energized so that current passes through bridge rectifier 24- 27 to energize the coil of an actuating relay 29. This causes braking of the directcurrent driving motor by short-circuiting its armature, for example, so that the driving motor is decelerated in proportion to its speed. A battery 9, which may be short-circuited by a variable resistor, provides a source of bias voltage to provide variable control of the operative conditions under which a decelerating signal will be produced by the comparison circuit. Similarly, a variable tap in resistor 11 or an attenuation device in the velocity signal circuit may be used for this purpose. In a modification (Fig. 4, not shown), the positional and velocity signals are respectively of the alternating-current and direct-current types, the direct-current signal being polarized in accordance with the direction of movement of the driven object. The negative and positive halfwaves of the alternating-current signal are separately rectified, and means are provided to compare like polarity signals derived from the velocity generator and positional generator respectively. For this purpose, the positional signal is applied to the grids of a double-triode valve having a common cathode connection to two oppositely-poled rectifiers which perform a function similar to that of the rectifier 12. The velocity signal is applied to the comparison circuit through oppositelypoled rectifiers which perform the same function as the rectifier 16. If the velocity signal has a rapidly rising characteristic it is not compared with the positional signal until a time delay has elapsed after a change of polarity of the velocity signal, so preventing hunting. A time delay relay, or a switch actuated in accordance with the driven object reading a predetermined position, may provide this delay period.