Patent GB-869224-A (GB)
Title: Improvements in or relating to interpolating devices especially for controlling automatic machine tools
Inventor: SPENCER ROLF EDMUND
IPC: G05B19/4105
Filed: 1956-07-10
Abstract: 869,224. Electric analogue calculating systems. ELECTRIC & MUSICAL INDUSTRIES Ltd. July 2, 1957 [July 10, 1956], No. 21280/56. Class 37. An interpolating device has three input terminals 1 to which are applied signals representing values of one co-ordinate of three given points P n-1 , Pn, P n-1 ; and a plurality of output terminals 3 from which interpolations are taken of one co-ordinate of points which lie, at will, on a parabolic or circular arc determined by the input signals. The applied signals, representing x coordinates, are fed from the input terminals 1 to an auto-transformer 2 having tappings connected respectively to the output terminals 3 by way of inductively coupled coils 4 the number of turns in which are related by a parabolic law as described in Specification 796,994; the centre coil 4 being inductively coupled to a similar coil 5. The voltages across the coils 4 correspond to the x component of the lift, at nine spaced points, of the parabola S, Fig. 3, above the chord K joining P n+1  and P n-1 . The difference in the x component voltages of P n+1  and P n-1  is fed to stator 6 of a resolver, and the difference in y component voltages is similarly fed from a corresponding y coordinate network to stator 7; the rotor 8 is thus maintained by servomotor 10, fed through amplifier 9, at an angle # to stator 7, where # is the inclination of the right bisector of chord K to the Y axis. Rotor 14 of a second resolver rotates with the rotor 8 and is thus similarly inclined to its stators 12, 13 which are fed respectively with the x, y components of the lift h/2 of P n  above the chord K so that the output from rotor 14 is the lift h/2 and this is fed to the rotor 15 of a third resolver having stators 16 and 17, the rotor being maintained at # + # to stator 17, where # + # is the inclination to the y axis of the radius vector from C to a point Q of the parabolic arc and C is the centre of the circle through P n+1 , P n 1, P n-1  such that P n P n <SP>1</SP> = h/2. The outputs from stators 16, 17 are the x, y components of a vector QP and. these components are added, at will by means of switch 26, to the corresponding parabolic components, the output from stator 16 being coupled through coil 18 to injector coils 19 in series with the parabolic coils 4, and the signals at the output terminals 3 correspond to the x components of a circular arc. The setting of rotor 15 is controlled by a fourth resolver the stators 20, 21 of which are fed with the time derivatives x, y of the x, y co-ordinates so that the rotor 22, together with rotor 15, is maintained at # + # to the y stator. The inputs x, y may be obtained from a linear sub-interpolating device, Fig. 4 (not shown), as disclosed in Specification 796,994. In the application of the present device to the control of a cutting tool, compensation for the tool radius is provided by feeding a voltage corresponding to this radius to a rotor 23 on the same axis as rotors 15 and 22; thus component correction voltages are obtained from stators 24, 25 for the x and y output signals. In another embodiment, Fig. 5 (not shown), the centre input terminal 1 is connected to the centre tap of auto-transformer 2 through two coils one of which is coupled to coil 18 thus obviating the need for injector coils 19. Specification 830,462 also is referred to.