Patent GB-693452-A (GB)
Title: Improvements in or relating to electric remote control systems
Inventor: JEFFERSON SIDNEY
IPC: B66C13/40
Filed: 1950-11-17
Abstract: 693,452. Electric correspondence control systems. HEENAN & FROUDE, Ltd. Nov. 16, 1951 [Nov. 17, 1950]. No. 28226/50. Class 40 (i) [Also in Groups XXXVII and XL(c)] A remote control system comprises a transmitting loop circuit TL, Fig. 1, mobile within a working area, and arranged to set up an alternating magnetic field, a control unit for modulating the loop current, and a receiver R connected to a receiving loop RL, surrounding the working area and adapted to control an apparatus 1 in accordance with the received modulation. The invention is described in connection with the control of a gantry crane, the various movements of which (e.g., hoisting, lateral motions, longitudinal motion) are controlled by' alternating or carrier currents of different frequencies of the order of 50kc/s. Extent of movement of a control member may be denoted by the number of pulses modulated on the carrier, and direction of movements by the kind of pulses, e.g., chopped and unchopped. Alternatively, different audio tones may represent different directions of movement. The receiving loop RL surrounds the area in which the gantry 1 is intended to operate, and the transmitter T, TL, is portable and batterydriven. The receiver R transfers the carriers through selective filters F and power lines 3, 4, to the controlled apparatus 1. Transmitter. Operation of a control lever on a shaft 30, Figs. 7 and 8, imparts a rotary movement through gearing 36, 37, to a shaft 30 which has a springy connection 43 to an aligned shaft 38a carrying a serrated cam disc 44. A rollerpressed inwards by a spring 50 and carried on an arm 45 hinged at 46, engages between the cam teeth and moves radially as the cam rotates, opening and closing contacts 52a and 52b to modulate the carrier source by a train of pulses, the number of which corresponds to the extent of the control lever movement. The direction of movement of the cam disc is sensed by an arm 59 frictionally driven thereby and carrying a stud 63 into engagement with one or other of two contacts 64, 65. Clockwise rotation of the control arm opens one of these contacts and results in the emission of unchopped pulses B1, B2, and anti-clockwise rotation opens the other contact and emits chopped pulses Cl, C2, as shown in Fig. 4. The control arm on the shaft 30 is returned to the central rest position by springs, 54, 57, coiled round the drum 34 with one end fixed to a frame member 32a and with their other ends bent at 55a to engage opposite sides of a radial member 58 on the drum 34. The springs thus return the shaft 30 to mid-position whenever pressure is removed from the control arm. Receiver. A received carrier is rectified and the resulting pulses are applied at the terminal 23, Fig. 6, to an amplifier 24 and a differentiating amplifier 25. If the pulses are chopped, both relays C/1 and VC/1 are operated, and terminal 27 is thus connected to earth. If the pulses are unchopped, relay VC/1 operates alone, and terminal 28 is connected to earth. Terminals 27, 28, are associated with stepping-motors 13, 16, Fig. 3, which are thus selectively operated according to the type of pulse received. Motor 13 drives a shaft 14 and drum 15 on which is wound a potentiometer resistor connected between sliprings 19 associated with a D.C. source. Motor 16 drives a shaft 17 carrying a slider 18 bearing on the potentiometer. The voltage between the slider 18 and the ends 19 of the resistor is thus a measure in sign and magnitude of the net angular displacement of the transmitter control, and is taken off by leads 22 to control the appropriate crane motor. In a modified control system, the transmitter employs three separate loops energized by three different carrier frequencies, Fig. 5 (not shown). The control switch, Figs. 13 and 14 (not shown), employs a sensing-disc frictionally driven by the cam and with a small freedom of movement limited by a pin and slot. This disc carries on its face two pairs of contacts which co-operate with stationary contacts connected to two tone sources of different frequency corresponding respectively with the two possible directions of movement of the control handle. The tone frequencies modulate the carrier as the cam roller is raised by the crest of each cam tooth, and the carrier is emitted continuously except when it is cut off by a short raised portion of the cam which engages the cam roller when the control is in the quiescent mid-position. At the receiver, the carriers are separated by carrier filfers and are rectified to yield the respective tones which are selected by tone filters and used to control the sense of the crane adjustment. Absence of carrier is used at the receiver to restore the control to mid-position.