Patent GB-872884-A (GB)
Title: Improvements relating to control devices for automatic machine tools
Inventor: VOLES ROGER
IPC: G05B19/4105
Filed: 1956-07-19
Abstract: 872,884. Copying-machines. ELECTRIC & MUSICAL INDUSTRIES Ltd. July 16, 1957 [July 19, 1956], No. 22338/56. Class 38 (6). [Also in Group XXXVI] A control device for an automatic machine tool comprises means responsive to a record for producing command signals representing two co-ordinates of points which describe a required locus, compensating means for deriving signals representing the components in the directions of said two co-ordinates of a signal which represents the radius of a cutter, which radius is orientated in a direction normal to said locus at the point defined by the respective values of the command signals, means for combining the signals from said compensating means with said command signals to produce control signals which if employed to control the displacement of the cutter relative to a workpiece in the direction of said co-ordinates would cause the cutter to cut a profile corresponding to the required locus and means for selectively reversing the effect of said compensating means-a phase-reversing memberwhereby the negotiation of sharp corners in said locus is facilitated. The machine tool is an automatic electronically controlled milling machine. The work-table W, Fig. 2, and a platform P therefor are made movable in the X and Y directions respectively so that the workpiece describes a locus having thereon points X, Y relative to the stationary tool, and signal components x, y are added to cause the movement of the workpiece to take account of the radius r of the cutting tool at points where there is a sharp continuous or intermittent change of slope at a corner in the profile to be cut, and sharp corners e.g. an outside corner or vertex are negotiated by the cutting tool, without difficulties caused in the prior art by the slowness in response of correcting circuits, by means of a phase-reversing switch 12. The sharp corner ABE, Fig. 3b and Fig. 4 (not shown) is negotiated by programming a locus ABCDBE for the cutting tool and by operating phase-reversing switch at points C and D so that the rotor 5 of the correcting circuit does not have to move at these points, thus eliminating the above referred to time lag. The portion traced out by the tool between points C and D may be a straight line, parabolic arc or other curve. For particularly acute-angled corners, Fig. 5 (not shown), the locus traced out includes two parabolic arcs. The circuit is operated by a tape T which gives command signals to interpolating means I1, 12 by means of tape readers T1, T2, the interpolating means I 1 , I 2  deriving A.C. analogue voltages representing the X and Y co-ordinates of the respectively desired locus and being mounted on a common rotating shaft S. Differentiating circuits D1, D2 derive X and Y which are fed to stator windings 3, 4 of a first resolver the rotor of which energizes servomotor 8 via amplifier 7 so as to rotate shaft 6 to an instantaneous dy angle of # = tan 1 -. This modifies the dx action of a second resolver having rotor 11 to which a signal representing the radius of the cutting tool is fed, signals representing r sin 0 and - r cos # being derived from stator windings 9, 10 respectively. Adders A1 now produce X + r sin # and Y - r cos # respectively from I1, 9 and 12, 10 respectively as in Specification 830,461 and are fed to difference circuits S1, S2 where they are combined with position analogue feedback signals the resultants energizing servomotors SM1, SM2 to move the platform and worktable respectively. Phase-reversing switch 12 is responsive to the programming fed to the interpolating means or to signals derived from an extra information track on the programme. During operation of phase-reversing switch 12 amplifier 7 is suppressed to avoid effects of spread in switch contact timing. Signals corresponding to a parabolic arc can be derived from the parametric interpolating device of Specification 830,462. The tool may alternatively move, the work-table and platform being fixed, as disclosed in the latter Specifications.