Method and apparatus for numerical control

Abstract

Method and apparatus for numerical control to produce contouring by simultaneous coordinated motions along two or more axes, characterized by the creation of desired velocity signals supplied as the primary inputs to velocity servos coupled to drive a member relatively along the respective axes. A digital computer associated with an adjustable interrupt clock which measures off successive time periods .DELTA.T, supplies a changeable velocity command number signal to each servo proportional to the distance per .DELTA.T through which motion along the associated axis is to occur. This velocity command number is algebraically added to a theoretical position number to signal dynamically during each period .DELTA.T the axis position at which the member should reside; and the latter number is used with a dynamically signaled actual position number to re-compute and signal during each period the position error. The position errors are used as a trimming or adjusting term in the signals applied to the respective axis servos. When the signaled error exceeds a first threshold on any axis, the periods .DELTA.T are lengthened to reduce all axis velocities; when it exceeds a second threshold, the system is put into a holding mode. The input signal applied to each axis servo includes a further historical adjustment term incrementally changed during any period when the error exceeds a predetermined value-- all to the objective of making the axis servos (a) operate with substantially zero following error, (b) correct themselves if the position error becomes at all appreciable, or (c) stop if that error becomes intolerable.