Patent GB-1158271-A (GB)
Title: Improvements in or relating to Data-Processing Systems.
Inventor: ECCLES EDWARD STUART
IPC: G06G7/48
Filed: 1965-05-18
Abstract: 1,158,271. Computer control systems. ROLLSROYCE Ltd. 15 Aug., 1966 [18 May, 1965], No. 21025/65. Headings G4A and G4G. [Also in Division G3] Under suitable conditions, certain of the calculations normally required to be performed repeatedly in cyclic sequence and in real time by a computer may be inhibited or modified, thereby releasing computer capacity for other computations. In an analogue arrangement for controlling a jet engine speed (Fig. 3) according to a throttle lever position control loop or a governor speed control loop, a computer selects which loop is operative at any one time. Function generators 13, 14 respectively generate normal operating engine speed governor signals and throttle position demand signals corresponding to the pilot's lever position. These demands are compared with actual engine speed and throttle position in error generators 16, 18. An error comparator circuit 21 compares the amplified signals and sets a switch 22 by means of a bistable relay D accordingly. Switch 20 already being set to its mid-position N, the selected signals are applied to the throttle servo-system 25. Under suitable conditions, e.g. when the throttle lever angle exceeds a critical angle #c as detected for instance by a microswitch, the error comparator 21 may be disabled by the control computer by way of switch 38 and OR- gate 37. At the same time, by way of relay D, the switch 22 is set to the position in which the throttle position control loop is inhibited. The loop in use at any given time is displayed by indicators connected to switch 28 ganged to switch 22. Switches 26 and 27 are provided for manual selection of the loop to be inhibited, but unless switch 22 is already in the position in which it is to be locked a signal is passed by way of switch 41 or 42 (ganged to switch 22) and OR-gate 43 to activate an output clamp bi-stable circuit 29 described below. The illustrated arrangement is capable of preventing surges and can change-over to the alternative loop on failure of one of the loops. Function generator 12 forms a speed demand signal to which an intake temperature and/or pressure bias may be applied. Failure of the throttle position loop causes computer closure of switch 10 and operation of relay A which sets switch 20 to position A, disables error comparator 21 and closes switch 31 to activate an indicator showing the crew that reversion engine speed governor has been selected. A further function generator to which signals #e are applied (15) computes a schedule for the engine throttle position demand from the actual setting at the instant of failure of the engine speed governor loop. On such failure, switch 11 is closed by the computer to operate relay B, disabling the error comparator 21, setting switch 20 to position B and closing switch 32 to provide indication to the crew that the reversion throttle position loop is selected. The bi-stable circuit 29 is also set controlling a clamp circuit 44 to clamp the output from switch 20 until calculation of the new schedule is completed (the clamp being released by computer closure of a switch 33). Simpler reversion schedules may be used. To prevent surges of power in such cases, means are provided whereby the error difference between the actual throttle position and the demand throttle position or the actual speed and the demanded speed can be indicated to the crew (switch 30 with alternative position), so that the pilot's lever can be moved, with switch 20 output clamped, to reduce the indicated error to zero. The clamp may then be released by manual operation of switch 34. In an acceleration loop control application (Fig. 6), the pilot's lever position is regularly sampled by a switch 120 controlled by a clock 128 and the sample signals are passed first to a store 121 and then to a second similar store 122. Difference signals from comparison circuit 123 are passed to a threshold detector circuit 125 and then to an integrator circuit 124 integrating over J cycles. Computation of acceleration error is inhibited until a signal is produced by way of summing amplifier 134 sufficient to operate a relay 126. A further sampling switch 132 is provided controlled by the clock 128 and feeding signals to an integrater 133 integrating over I cycles, where I<J. A signal is applied to switch 132 via summing amplifier 135 whenever either the acceleration control loop or other associated loop (e.g. rate of change of turbine entry temperature control loop) is selected for control purposes. Signals are also applied (of equal value) whenever errors on any loop associated with steady running of the engine are in excess of threshold values representing steady running conditions. With the above arrangement, the relay 126 is not released either during an acceleration or surge suppression operation or until the errors on the steady running control loops have returned to steady running values. Computer time freed by the above techniques may be used amongst other things for analysing data required to be recorded during flight, thereby effecting considerable storage compression. The invention may be applied to control by digital computers also.