Patent GB-1481739-A (GB)
Title: System for numerical control of a machine tool
IPC: G05B19/42
Filed: 1974-10-16
Abstract: 1481739 Automatic machine tool control HAMILL CO INC 16 Oct 1974 [29 Oct 1973] 44927/74 Heading G3N In a numerical control system for the relative movements of a cutting element { of a lathe,  milling machine, grinding machine or drill press}, the programme is prepared by an operator, using manual controls (21-23), Fig. 1 (not shown) to establish a set, of sequences each defined by an end-point of a movement, the set being stored in a computer for use in machine control and constituting a program. Sequences appertaining to conjoint X-Y components of movement are stored as sequences distinct from those relating to Z components of movement, although the latter may be interleaved with the former to define a three-dimensional contour. X-Y movements take place in increments, in ŒX;ŒY; or ŒX with ŒY, directions in linear or circular interpolation. In establishing an X-Y sequence, the operator selects the speed and direction of approach to the end-point. The computer may ensure that, for each such sequence, the initial part of a movement from the end-point of a previous sequence takes place at a predetermined speed, with a ramp down in speed to the end-point of the current sequence. Any Z sequence may be performed in a "peck" mode, as a single movement, or for each increment, there may first be a retreat to the end-point of the previous sequence, followed by an advance to the current incremental point, to allow chip removal. For overall speed control, some sequences may constitute null motions, the sequences being processed at a clock rate. Sequence Edit. Each sequence has an identifying number, and can accordingly be called up by the operator, for either correction, or replacement by a new sequence. Entirely new sequences may be added, the identifying numbers of all subsequent sequences being increased. During running of the program, the operator can switch to edit at any sequence, for correction, addition or deletion, each sequence, for such a run, containing data enabling the next sequence to be performed, the mode switching to edit in the absence of such data for any sequence. Programs may be stored on tape, in unit (42), Fig. 1. A given sequence may be repeated 1 or more times, or a given number of sequences at the end of a program may be repeated. Facility is provided to translate; or reflect in x, y or x and y; data sequences so that a given operation can be performed at a plurality of sites, or sequences for a given workpiece portion may be utilized in producing workpieces with mirror symmetrical portions. Two or more machines may be controlled. Circular interpolation:- For any X-Y sequence to be so performed, the entered data includes centre, radius, and sense { clockwise or counterclockwise } of the curve to be followed to the sequence end-point. When such a sequence is called up, the cutting element may be fully retracted in the Z direction, or remain stationary, a workpiece table, moving in the X-Y plane, attaining the circular contour at either end-point, or an intermediate point, Fig. 4 (not shown). Tool offset. With each sequence, the operator may include tool offset data, allowing for cutting edge wear during performance of a program, Figs. 5a, 5b (not shown). Backlash control, when operative for any sequence, its end-point is approached always in a set direction.  Drive arrangements. With each axis is associated a stepping motor drive, and an encoder and pulse generator producing phase displaced {defining motion direction , pulse trains, see Fig. 2 (not shown). Command data is received from the computer via a data buffer into an up/down counter also receiving the pulse trains. Should the counter contents be too great or too small e.g. if a movement is prevented, a stall warning is given and the machine stops. Displays and warning lamps are provided, Fig. 3.