Patent GB-643381-A (GB)
Title: Improvements in or relating to apparatus for determining the maintenance of or departure from a predetermined relationship between two variables
IPC: G01S1/02
Filed: 1947-06-06
Abstract: 643,381. Automatic control systems for aircraft. DECCA RECORD CO., Ltd., ROBERTS, G. E., and SANDERSON, W. T. June 6, 1947, Nos. 15007, 15038 and 18200. [Class 38 (iv)] [Also in Groups XIX, XX and XL (c)] The invention relates to indicating apparatus for showing the progress of a craft along or its deviation from a predetermined course. Such apparatus may be operated by the receiver of a radio-navigation system, for example a hyperbolic navigation system such as is described in Specification 620,479. In its broadest form the apparatus determines the maintenance or departure from a predetermined relationship between two variables and comprises two indicating members moved at rates proportional to the actual changes in the variables (for example the changes in the phasemeter readings in the system referred to) transverse to and overlapping one another. The members are either each provided with a traverse line so that the point of intersection of the two lines moves over a chart or track plotted in appropriate co-ordinates to represent the desired relationship or one of the members is provided with a contour line representing the relationship while other is provided with a marking which will lie on the contour line so long as the desired relationship is maintained. The indicating members may comprise transparent strips and in the aforementioned system one of the strips may carry an indication of the course plotted on rectilineal co-ordinates corresponding to the hyperbolic co-ordinates of the system and the other, one or more markings which coincide with the indication when the craft is on the course. In a development of the navigation system one master station and 3 slave transmitters approximately regularly angularly spaced round the master are used providing three pairs of signals on the craft and three phase difference values. If desired suitable pairs of these values may be chosen to give the most satisfactory mark-ings on the strips, alternatively the three values may be combined into two which are used to operate the indicator. One way to do this is to number the hyperbolic contours outwardly from the master station and regard each meter reading as a vector having a direction parallel to the corresponding master-slave base line, then one combined co-ordinate may comprise the scalar sum of the three values (14 in Fig. 16 where the co-ordinates are referred to in terms of colours) and the other the angle between the starting (red) base line and the vector sum of the three valaea (# in Fig. 16). The two co-ordinate pattern formed by this means is similar to a polar co-ordinate pattern but distorted by any lack of symmetry in the transmitter layout. In a variation the vector sum 122 instead of the scalar sum may be used for one co-ordinate. Circuits for deriving the combined co-ordinates to be used to operate the indicator are described with reference to Figs. 17 and 18 (not shown), and further ways of combining three co-ordinates to obtain two are also suggested. The indicator. Fig. 1 shows one form of indicator with film strips 12 and 13 tensioned across a box 10 containing a light source and provided with a viewing hood 11. The line representing the course is normally inscribed on the film on which it will make least angle with the direction of movement and may be in any number of sections changing from one film to the other as required. Each section requires a corresponding mark on the opposite film. To avoid confusion between the various route sections marked on the films each film is divided into two separate parts, each of which is printed with course markings and reference marks in complimentary colours and may be illuminated by either of two coloured lights to pick out a required portion of the course. Fig. 3 shows a portion of a film strip with two sets of course sections 52, 78 and the like marked thereon and also marks 72, 87 and the like which co-operate with route sections on the other film. The bottom of the hood 11 is provided with a mask, Fig. 7, provided with, apertures 30, 31 through which the films may be viewed. Two differently coloured lights of complimentary colours may be switched on alternately as required under each of the apertures to make visible the course or mark in the oppositely coloured ink so that any of four recorded courses may be made available. Other markings on the film visible through apertures 55 or 73 provide the pilot of the craft with other information for example distance along course. The navigation system meter readings are also shown as scales on the films and a second film driven in synchronism used to display non-permanent information about conditions along the course. Film strips of parts of a desired course of special interest on a greater scale and moved at a greater speed may also be used and endless bands marked with fine lines arranged above the normal strips may indicate position in respect to charts representing airfield approaches. In the alternative arrangement wherein the indicating members carry lines only and films or the like carrying the chart information are inserted beneath them the drives for the two members may include devices varying the speed to allow for variation in the contour line spacing of the navigational system pattern. The drives may also be interconnected to allow for the angle of intersection of the contour lines not being a right angle (Fig. 13, not shown). The maps used may then be of more normal form. Fingers co-operating with holes in the films may be used to change the colour and position of the illumination automatically in the first described arrangement and a similar arrangement co-operating with indentations in the side of the maps used to set the correct drive speed and interconnection arrangements in the second embodiment. Automatic control of a craft. If the indicator is to be used to automatically control the movement of a craft the film on which the location marks are made is uniformly coloured except for small transparent circles for the actual marks. The other film on which the course is marked comprises a film having uniform predetermined density along the course line and higher density to one side and lighter to the other. There is also a comparison standard in the form of a narrow channel down the strips. Photo cells responsive one to light passing through the comparison channels and the other to light passing through the rest of the film area are arranged in a bridge circuit which is unbalanced when the cells do not receive light in a predetermined relationship. Unbalance current occurring in the bridge circuit due to deviation from the predetermined course may be used to operate an auto-pilot to correct the course being navigated. In such an automatic system if the craft is so far off course that a different mark comes close to the track a completely incorrect course might be flown and so the apparatus is duplicated and a second apparatus whose strip scale is, <SP>1</SP>/ 16  th of that of the first given an overriding control over the automatic pilot.