Patent GB-1236671-A (GB)
Title: Machine tool control system
IPC: G05B19/39
Filed: 1969-01-06
Abstract: 1,236,671. Programmed control of machine tools. INTERNATIONAL BUSINESS MACHINES CORP. Jan. 6, 1969 [Jan.15, 1968 (3)], No.756/69 Heading G3N. In a programmed control system providing a series of command words through a channel register for controlling co-ordinate movements of a machine tool from input signals indicative of the speed and displacement of each axis, a register stores each of the command words in sequence and comprises part of a computer linked to a data storage unit so that the computer generates command words in response to the speed and displacement signals, which words are stored in output buffer tables in the storage unit, the arrangement having external pulse-generating means e.g. a variable frequency oscillator producing signals controlling the transference, at variable rate, of command words from the buffer tables to the channel register. A numerical control system for controlling one or more machine tools 22, 23 has a processing unit 6 fed from a card or magnetic tape reader 4, a secondary disc store, also an internal memory 27 supplying information to channel units e.g. 10, one for each machine, which can read from and write into the internal memory synchronously with the operation of processing unit 6 on a time division basis. Each channel unit has an output register connected through a transmission control unit e. g. 14 which amplifies and shapes the words received from the output register for transmission to a machine control unit 18 which controls co-ordinate axes of the machine. Unit 14 also passes pulses from an oscillator to each channel unit causing new words to be entered sequentially in the output register. The machine unit 18 also filters out noise and checks signals for parity and validity, correct signals being passed to the machine and incorrect signals causing a resampling, corrective action or machine stoppage. In a known machine control system, co-ordinate movements are incremented into X, Y, Z registers see Fig. 2 (not shown) at a rate determined by a pulse oscillator, and "spill over" above a determined number e.g. "1" causes a corresponding command to be forwarded to the machine control unit. This entails an addition for every pulse and furthermore a number of the command words are null i.e. have no information. In the arrangement disclosed, the axis movements are divided into velocity components which are related to the axis having the maximum velocity, and the pulse output is divided in proportion to the ratio of required speed to maximum speed. The advantage lies in the elimination of null command words, which enables a smaller store to be used. If null words would appear alternatively in the maximum system, the output of the pulse oscillator is divided in the same ratio to bring the effective words forward at the desired rate. This enables a smaller store to be used, see Fig 4 (not shown); samples of command words of all effective types are stored and brought out as required. As the oscillator output can only be divided by a whole number, a high basic frequency is empolyed e.g. kc/sec. which is divided at the maximum speed requirement by 64, or by higher numbers for lower speeds, resulting in a periodic pulse train giving uniform servo action. Methods of interpolation are described in the Specification.