Patent GB-1372291-A (GB)
Title: Numerical control contouring systems
IPC: B23Q15/013
Filed: 1972-01-25
Abstract: 1372291 Program control of tool motion. ALLEN-BRADLEY CO 25 Jan 1972 [25 Jan 1971] 3512/72 Heading G3N In a numerical control contouring system in which digital differential integrators (DDI's) for a feedrate number F (FRN) and for X; respectively Y, Z; movements are in series to modify the rate of a clock pulse train, see also Fig. 1 (not shown), the overflow from overflow register 34, for each axis, controls a corresponding servomotor, and decrements the axis command data until the latter reaches zero. Normalization circuitry enables the timing of the overflow, during the recirculation of the axis integrand register 28 to be varied in dependance upon the number of leading zeros in the contents of registers 18 and 28 to provide for more rapid tool movement, and in the absence of a feedrate number, allows for rapid tool traverse within specified ranges. Feedrate number DDI, 18, 20, 22 see also Fig. 5 (not shown). Feedrate data from source 87 is fed in complementary form to integrand register 18. In operation the data is recirculated in register 18, and the content of 18 is added to accumulator register 20 by adder 22. Via flip-flops 80, 82 the carry output (C n+1 ) of the adder is sampled, and under control of pulses on line 24, initiated by the normalization circuit, Fig. 8A (not shown) signals are fed to the contour generators. X Contour Generator DDI, 28, 30, 32, 34, see also Figs. 6A, 6B, 9 (not shown). The axis DDI is similar in function to that for feedrate; the overflow, from carry output (C n+1 ) being however fed to a 5 bit shift register whose loading, and unloading to control machine servos is controlled in timed sequence on line 42, see also Figs. 7A, 7B (not shown), such pulses being provided by means of counter (274), Fig. 8B (not shown). The overflow downcounts shift register (124) Fig. 6B, (not shown) initially containing the axis command number, and logic circuitry detects when it has been counted to zero, with the possibility of correcting the servosystem should register (124) count below zero. By variation in the timing of pulses 24 and 36, the effective lengh of the DDI registers may be varied to alter the speed of system response. The respective axis contour generators may operate independently for linear interpolation, or, by controlling cross feeding between a pair (i, j) Fig. 9 (not shown) generators, circular interpolation maybe obtained, unit (309) defining the rotational sense of such interpolation. Normalization, Figs. 8A, 8B (not shown) (I) Normal traverse. During a timing interval (2T) see also Fig. 4B (not shown) equal to the register recirculation time, counter (178, 180) counts up for zeros in the feedrate number, and is cleared if a "1" occurs, and thus at the end of (2T) stores the number of leading zeros in the FRN. Simultaneously, axis counter (222, 224) is set to store the complement of this number, and the state of these counters governs the timing of the enabling pulses for axis overflow by allowing the latter when counter 222 reaches a predetermined count value. (II) Rapid traverse Provided that there is no unity digit in the FRN, integrand register counter (224 222) counts up, via gates (250, 252, 254) unless a "1" appears in anyone axis integrand register whence it is reset. Thus it stores the least number of the leading zeros in the axis integrand register. The extent of normalisation is governed by the nature of the connections from the counter (222, 224) to the axis overflow enabling outputs. Timing circuit, Fig. 3 (not shown), comprises a crystal oscillator, series connected J-K flip-flops and a 5-bit shift register, to provide the time correlated pulse waveforms of Figs. 4A and 4B (not shown) used in system control.