Patent GB-1170266-A (GB)
Title: Numerically Programmed Digital Continuous-path Machine Tool Control System
IPC: G05B19/4103
Filed: 1966-11-03
Abstract: 1,170,266. Programmed control of machine tools. BROWN, BOVERI & CO. Ltd. Nov.3, 1966 [Nov.5, 1965], No.49344/66. Heading G3N. A numerically programmed digital control apparatus for producing movement of a machine tool member along a desired path relative to first and second co-ordinate axes comprises a function generator for storing data relating to a reference circular arc which is responsive to programmed signals to produce signals relating to movement along a polygonal path approximating to selected section of the arc. As shown, for each axis of movement a speed counter GZ is cyclically counted down to zero from a set value by pulses from an oscillator O. At each zero count a pulse is generated by the counter GZ which is applied (1) to count down a step-counter SZ from a set value and (2) to a difference counter DZ of an axis positioning servosystem ORK. At zero count, the step counter SZ generates a signal which closes a gate T3, through a gate T2, to stop the supply of pulses to the speed counter GZ. When the signals from the step counters SZ for both axes exist at the input to a gate T4 a function generator FG is stepped to set up new initial counts in the counters GZ, SZ. The function generator FG comprises permanent stores FS and MP which determine the initial counts in counters GZ, SZ whereby a controlled machine tool member follows an approximation of a section of a quadrantal arc in the form of a polygonal progression consisting of chords, each corresponding to a constant small angle. The step counters SZ contain an initial count corresponding to the differential amounts of traverse along the X and Y axes for a step in dependence on a particular angle. The speed counters GZ contain an initial count dependent on the sine or cosine of the step angle for the X or Y axis, respectively. The store FS comprises code discs, driven by stepping motor, bearing incremental binary coded decimal values for constant angle points along a quadrantal arc of a circle of unit radius. The stepping motor is positioned by a programmed angle signal. The BCD values drived from the coded-discs, by a contact-making element, is multiplied in a multiplier MP with the programmed radius. The programmed angle and radius values are derived from a punched-tape reader, not shown. Further code-disc, coupled to the stepping motor, bear the sine and cosine values for the speed counters GZ. The programmed velocity is fed to a delay device VR controlling a converter W changing the pulse rate from the oscillator O by selecting frequency determining capacitors. For small sine and cosine values, a signal from the function store FS actuates a change-over switch US1 whereby the pulse rate is reduced by a factor of 10, as necessitating the code discs to be made for three significant figures only. The difference counter DZ of the servosystem is fed with actual position pulses Mx, My and the error through a digital to analogue converter DA controls an axis positioning motor M, feedback being provided by a tachogenerator T to a servoamplifier RV.