Patent GB-1323731-A (GB)
Title: Control method and apparatus for numerically controlled machines
IPC: G06K15/22
Filed: 1970-06-29
Abstract: 1323731 Recording - apparatus BAUSCH & LOMB Inc 29 June 1970 [27 June 1969] 31319/70 Heading G1J [Also in Division G3] A method of coding and arranging digital characters to provide signals defining, relative to mutually perpendicular axes, a path of movement to be followed by a numerically controlled machine (such as a graphical plotter or machine tool) comprising (a) assigning a different digital character to each of a number of plot commands each corresponding to a different direction of incremental movement along the path; (b) assigning other digital characters to each of a number of step commands each corresponding to a fixed number of increments of movement along the path; (c) coupling any one of the digital characters in (a) with any one of those in (b) to produce a signal representing a digital plot couplet which defines a path having a fixed direction and length; and (d) applying the signal to the machine so that it allows the path defined by the couplet. Apparatus 126 for controlling a graphical plotting machine 100 comprises: (1) a routing logic circuit 302 responsive to electrical signals for differentiating between and segregating those representing (a) digital control characters and (b) digital plot characters from those representing (c) digital step characters (2) a command logic circuit 318 responsive to the signals for control and plot characters for decoding and segregating (a) and (b) (3) a plot clock 350 and plot clock control and register 326 responsive to the signals for the step characters (c) for generating a train of pulses equal in number to the number of steps specified by the detected character; and (4) a gate circuit 348 responsive to the last pulse of the train to inhibit generation of further pulses. the arrangement being such that the plotter 100 plots in the direction specified by the decoded digital plot character for the number of increments specified by the digital step character for each couplet or pair of such characters represented by electrical input signals. The plotting machine 100 is prepared for plotting in the direction specified by the digital plot characters through selected gates 360 to 370, after decoding by circuit 18. When a couplet is decoded by circuit 18 the step command passes via lines 303b to 307b and a memory circuit 324 to the register 326 to start the count down of pulses from clock 350, meanwhile the direction command has been set via lines 400 to 403 and with x gate 360 and y gate 361 both up for the plot mode of the apparatus, the machine 100 plots the specified number of steps in the specified direction e.g. between one and thirty steps in one of eight directions. The number of commands needed to control plotting is reduced by including in the code for associating digital characters with commands, digital tacking characters and digital repeat characters. A tacking control logic circuit 344 responds to a tacking character decoded by circuit 18 by shutting down one of the gate circuits 360, 361 for the last step count only to alter the direction of the plot for the last increment specified by the step command. A repeat character specifies the number of times a plot command and its associated step command are to be repeated and when decoded by circuit 318 a signal passes via line 406 to the register 326 and to a repeat control and count register 328 to inhibit the register 326 and gate open the register 328. Each time the plot clock 350 counts down to zero from the specified number of steps the last signal is sent via line 333 to register 328 which counts down to zero from the specified number of repeats, a slewing mode may be switched onto increase the speed of plotting long lines in one direction. A pen up, pen down timing circuit 332 associated with gates 372, 374 and lines 404, 405 allows for plotting movements with or without marking e.g. for initial setting. Blocks of information to be plotted may be coded on magnetic tape for play back by a unit 300, each block being provided with a digital address character. In a search mode of operation (314) of the apparatus, a logic circuit 320 receives from the unit 300, via lines 303c to 306c electric signals corresponding to digital characters and compares the block addresses with those selected in a switch unit 310 for plotting circuit 320 then switches the apparatus over to the plot mode (315) and a tape unit control logic circuit advances signals to the routing logic circuit 302.