Patent GB-848647-A (GB)
Title: Apparatus for controlling relative motion by electric pulses, especially for automatic machine-tool control
IPC: G05B19/25
Filed: 1958-08-12
Abstract: 848,647. Programme controlled milling-machines. BENDIX AVIATION CORPORATION. Aug. 12, 1958 [Aug. 22, 1957], No. 25896/58. Class 38 (6). In a programme controlled milling-machine on which movement of the tool along the 3 control axes is effected by motors responsive to incremental command pulse trains, and the numbers of pulses in each train are determined by 3 binary digital coded recorded programmes defining a series of co-ordinates of the tool path, the frequency of the incremental command pulses, and hence the rate of feed of the tool is determined by a fourth binary digital programme recorded on the same punched or magnetic tape as the 3 co-ordinate defining programmes. The x, y and z coordinate signals and the feed-rate signals are in the form of blocks of 21 digit binary code fractions on a punched tape 24 which is read block by block and the 4 addresses temporarily stored at 26: When required, the addresses are passed to magnetic core recirculating registers 30, 32, 34 and 28, respectively. To obtain the incremental command pulses, a train of timing pulses is generated at 39. This is multiplied at 28 by the feed-rate signal-which is provided in the form of a binary fraction-to produce a train of feed pulses of appropriatelyreduced frequency. The multiplier circuit is disclosed in Specification 848,646. This multiplier allows one feed pulse to be emitted during the course of selected recirculation cycles, but the time position of such a pulse within its cycle may vary. A synchronizer 40 is therefore provided which delays the feed pulses and releases each one at the same time position in its particular recirculation cycle. The time position chosen is the one at which the first "one" emerges from any one of the 3 storage registers 30, 32, or 34. The synchronized train of feed pulses is in turn multiplied at 42 separately by each of the 3 co-ordinate position signalsagain provided in the form of binary fractions stored at 30, 32, 34-to produce 3 command pulse trains having frequencies related to each other in the ratio of the magnitudes of the 3 coordinate position signals. The multiplier 42 is similar to the feed-rate multiplier 28. By stopping the multiplier 42 when it has received 2<SP>N</SP> pulses, where N is the number of digits in the longest of the 3 co-ordinate position signals, each command train will contain the appropriate number of pulses. In order to keep down the frequency of pulses handled by the multiplier stages, the feed-rate binary code number is always treated as though it contained no more than 18 out of a possible 21 digits-i.e. as though the timing pulses are to be multiplied by 1/16 or smaller fractions. When the feed rate is in fact larger, the omitted digits are detected and the 3 trains of command pulses that form the final answer are multiplied at 45 by 2, 4 or 8 as appropriate for 19, 20 arid 21 digit feed rate codes, respectively. When this multiplier 45 is in use, it is necessary for the 3 co-ordinate position signals to be divided by 2, 4 or 8 as appropriate, otherwise both the feed rate and the position would be increased. This is achieved by omitting digits from the co-ordinate position signals. The three? outputs of the pulse multiplier 45 are each fed to one of three digital servos 46, 48, and 50 which also have an input from the tape reader 26 indicative of the " sign " of the required movement. Specification 829,824 also' is referred to.