Patent GB-984780-A (GB)
Title: Improvements in or relating to hyperbolae plotting instruments
Inventor: COOP ERIC
IPC: B43L11/02
Filed: 1962-09-26
Abstract: 984,780. Drawing or plotting hyperbolae. MINISTER OF AVIATION. Nov. 15, 1963 [Sept. 26, 1962], No. 36506/62. Heading B6P. An instrument, Fig. 8, for drawing an hyperbola comprises two bars A, B ; C, D respectively, in non-sliding driving engagement with rollers R1, R2 and R1, R3, the rollers being all of the same effective radius. When rollers R2, R3 are rigidly attached to a plotting table and roller R1 is moved about, the centre O of the latter describes an hyperbola, the foci of which are the centres P1, P2 of rollers R2, R3. The instrument uses the property that the difference between the distances of any point on a hyperbla from the two foci is constant. The rollers may be pinions engaging racks on the bars. The above principle can be extended to plot the intersection of two specified hyperbolµ, Figs. 1, 2, 5 and 7. In this form, the three foci of two hyperbolµ having a common focus are defined by pinions such as 30 (Fig. 1) in each casing 46, 28, 37. These casings are each mounted on sockets 81 (Fig. 5), having points 55 for insertion in the table and interconnected by articulated struts 56, 33, 34, 43. By tightening clamps such as 82, 100, 101, the sockets and struts can be set in adjusted position. By tightening clamps such as 53 the pinions 30 can be locked on the sockets 81 and hence rigidly attached to the table. Casings 28, 37, 46 are rotatable relative to the pinions 30. Bars 1, 2, 3 extend from the casings 28, 37, 46 to casings 15, 20, 23 mounted rotatably in superposed relation on shaft 17. These bars carry racks 5, 7, 9 meshing within the casings with pinions 12, 19, 22 all fixed to shaft 17 to form a common roller. Bars 1, 3 pass through casings 28, 37 and their racks 5, 9 mesh with pinions 30. Bar 2 however overlies casing 46 and a short rack bar 51 meshes with pinion 48 in that casing. Bar 2 carries a rod 58 slidable on which is a cursor 59 having an index P and bar 51 has a marker 60 having an index M. In each casing, the relevant bar is held in engagement with its pinion by the engagement of an opposite rack 4, 6, or 8, with further pinions such as 18 (Fig. 2), rotatable in the casing. Each pair of pinions is geared together. In a modification, the rack may be provided along one edge of a slot in the bar and is held in engagement with the pinion by spring means, the auxiliary pinions such as 18 being dispensed with. A stylus 27 can be inserted through hollow shaft 17 to mark the plotting table with the intersection of the two hyperbolµ when the points 55 of the casings 28, 37, 46 have been set at the three foci in the following manner. By undoing the clamps 53 completely, the sockets 81 and struts 56, 33, 34 and 43 are separated from the rest of the instrument. This unit is then mounted on the table with the pins 55 at the three foci and the parts are locked by tightening clamps 82, 100, 101; the casings and bars are then remounted but clamps 53 are not tightened. The short bar 51 is moved to about its mid-position in casing 46 and bar 1 is moved so that casing 28 is near its end; the pinions 30, 48 in these casing are then clamped. A gauge (Fig. 7) is mounted on the instrument with its hole 64 and pivot-pin 65 engaging pin 54 on casing 46 and hollow shaft 17 of casings 15, 20, 23 and with its slot 66 engaging a pin concentric with pinion 30 of casing 28. Shaft 17 is now rotated by knob 26 until the last-mentioned pin registers with that point on scale 67 of the gauge which gives the specified difference between the distances of the curve from the foci. The index P on cursor 59 is then set against the index M on short bar 51. The procedure is repeated for bars 1 and 3 using the gauge to set the distance difference specified for the second hyperbola and the pinion 30 in casing 37 is clamped. The gauge is removed and knob 26 is rotated until the indices P, M again coincide. The axis of shaft 17 will then line on the intersection of the two hyperbolµ and this point can be marked through the hollow shaft. By correlating the scales on the gauge and plotting table with time or phase of radio signals, the instrument can give a plot of the position of a transmitter or receiver relative to the positions of three receivers or transmitters respectively. In the form shown in Fig. 10, rollers R1, R2 and R3, and bars A, B; C, D, and rollers R1, R4 and R3, and bars J, H; C, D constrain the centre O of roller R1 to lie at the intersection of two hyperbolµ the path differences of which are displayed by indicators M1 and M2 geared to rollers R2 and R4. By unclamping these rollers and rotating them the hyperbolµ may be altered. They may be altered by servo mechanism controlled by signals from a radio navigation system to provide a flight log plotter. Specification 342,893 is referred to.