GB1014397A - Improvements in or relating to servo-motor control systems - Google Patents

Abstract

1,014,397. Automatic controL FLIGHT REFUELLING Ltd. Sept. 3, 1964 [Sept. 8, 1963], No. 18190/63. Heading G3R. In a servomotor system for controlling variables, operation is in response to the unbalance of two mechanical forces, one dependent on the value of one of a plurality of selectable variables and the other dependent on the value of one of a plurality of selectable reference values. As shown, the pitch of blades 14 of an air turbine 11 on an aircraft is adjustable by a reversible hydraulic servomotor 15 so that capstans 12, 13 and a reel 10 are driven in one direction or the other to pay out or reel in a target (not shown) which is towed behind the aircraft on a cable 32. The tension in cable 32, which is caused by the difference in speed between capstans 12, 13 and reel 10 produced by a variable speed gear 28, is automatically maintained at a preset value by the loop tension detector shown controlling the variable speed gear 28 through a potentiometer, amplifier, electromagnetically operated control valve 34, and hydraulic servomotor 35. When the target is initially released from its support on the aircraft, a controller 46 selects the signal from a loop tension detector 39 for comparison with one of the signals from a group of preset potentiometers 42-45 so that tension is maintained at a predetermined minimum value by differential control of a hydraulic valve 16 associated with servomotor 15. When a predetermined speed of paying out is reached a tachometer generator 40 and another of potentiometers 42-45 are substituted in the control of servomotor 15 so that the speed is maintained constant until a predetermined length of cable, as detected by a pulse generator 53, has been payed out. Control of servomotor 15 by tension detector 39 is then restored but with a different preset potentiometer 42-45 so that tension is maintained at a higher value. In consequence, paying out slows down and changes to reeling in, whereupon a direction sensitive tachometer generator 54 causes application of a brake and feathering of the turbine blades to terminate control. A similar sequence of control for reeling in is described. The turbine is also stopped by the operation of a switch 50 if the cable breaks.