Patent GB-674197-A (GB)
Title: Improvements in computing devices
Inventor: MEREDITH FREDERICK WILLIAM
IPC: G01C9/00
Filed: 1949-12-15
Abstract: 674,197. Analogue electric calculating-systems. SMITH & SONS (ENGLAND), Ltd., S. Sept. 7, 1950 [Dec. 15, 1949], No. 32180/49. Class 37. Relates to an electric analogue computer for computing the attitude in space of a body, e.g. an aircraft, from A.C. inputs proportional to the known rates of turn of the body about the body axes. If the rates of turn of an aircraft about its roll, pitch and yaw axes are p, q and r and its instantaneous attitude in roll, pitch and yaw with respect to axes fixed in space is #, # and #, then the six quantities are related by the following equations As shown in Fig. 1, the computer comprises three interconnected channels dealing respectively with pitch, yaw and roll signals. The top channel comprises a pitch-rate (i.e. q) input 1 and an amplifier 11 controlling the speed of a motor 5 such that the instantaneous angular position of its output shaft 18 is proportional to #, said shaft driving a tachometer generator 8 to produce an A.C. signal proportional to #À; corresponding components in the other two channels are denoted by references 2, 12, b, q and 3, 13, 7, 10, respectively. As shown, the q and r are applied to a magslip-type resolver 4, Fig. 3 (not shown), ganged (dotted lines 22) to the # shaft 20 producing an output (q cos # - r sin #) which is applied to the # amplifier 11 together with the #À output from generator 8, the two inputs being in opposition so that the servo loop 11, 5 and 8 will be in equilibrium when the resultant input to amplifier 11 is zero, thus satisfying equation (1). A second output (q sin #+r cos #) from resolver 4 is applied to the # amplifier 12, the feed-back signal in this case being #À cos 6 obtained by applying the #À output from generator q to a resolver 14 ganged (dotted line 21) to the # shaft 18 so that equilibrium of the servo loop 12, 6, 9, 14 satisfies equation (2). The second output (q sin #+ r cos #) from resolver 4 is also applied through a buffer stage 16 together with input p to a resolver 17 producing outputs p cos 6 + sin # (q sin #+r cos #) which are added and applied to the # amplifier 13, the feed-back signal #À cos # being produced by resolver 15 which is similar to resolver 14 so that servo loop 13, 7, 10, 15 satisfies equation (3). Thus the system reaches an equilibrium state when equations (1), (2) and (3) are satisfied so that if the shafts 18, 19 and 20 are set in accordance with the initial attitude of the aircraft their settings will continuously represent the aircraft attitude. Equations (2) and (3) may be written and equations (1), (5) and (6) may be solved by the modified arrangement in Fig. 2 in which the servo loop 11, 5, 8 of Fig. 1 which comprises a velocity servo or integrator is denoted by 623, corresponding integrators in the # and # channels being shown at 24 and 25. In this case the second output (q sin #+r cos #) from resolver 4 is applied to a high-gain negative feed-back amplifier 26 having a resolver 27 (ganged to the # shaft 18) in the feed-back path so that the feed-back signal is cos x, where x, the output signal, is equal to and is applied to the integrator 24 to satisfy equation (5). A second output from resolver 27 equal to sin x, i.e. tan 6 (q sin #+r cos #), is combined with input p and applied to integrator 25 to satisfy equation (6). Both the above systems fail to fuction in the neighbourhood of #=Œ#/2 and this may be overcome by connecting a reversing switch in the output from amplifier 26, Fig. 2, the switch being actuated by a cam on the # shaft 18 as # enters or leaves the range - #/2 # # # rr/2. Suitably wound potentiometers may be used in place of resolvers but the permissible range of # is then more restricted.