Patent GB-906271-A (GB)
Title: Improvements relating to automatic control systems, especially for machine tools
Inventor: SPENCER ROLF EDMUND
IPC: G05B19/4105
Filed: 1957-08-09
Abstract: 906,271. Numerical control systems. ELECTRIC & MUSICAL INDUSTRIES Ltd. Aug. 5, 1958 [Aug. 9, 1957; May 3, 1958], Nos. 25143/57 and 14194/58. Classes 38 (6) and 40 (1). In a control system for positioning a machinetool in accordance with recorded binary pulse code signals, the command signal corresponding to the most significant digit is automatically cancelled by the corresponding movement of the work-table so that the " fine " control which corresponds to the remaining digits takes place about a " floating " zero instead of an " absolute " zero. In one embodiment, Fig. 1, a motor 1 drives a work-table 3 and positional feedback devices S1 and S2. The motor 1 is controlled by a comparator 14 in accordance with the difference between command and positional feedback signals, and includes an interpolator 15 of the kind disclosed in Specification 830,462, but the operation of the interpolator will be ignored as it does not affect the basic principles of the present invention. Coarse control.-The most significant digit of the recorded code signal causes in an undisclosed manner, a selector 21 connected to the comparator 14 to be positioned on a selected one of a bank of contacts D0 . . . D9, each one of which is associated with a particular one of a bank of wipers A0 . . . A9 which co-operate with tappings C2 ... C8 on a transformer winding T1. The winding T1 has a centre tap C5 permanently connected to the other side of comparator 14. The wipers A0 . . . A9, which are in fact rotary, though shown linear for convenience, are driven by the device S1 in accordance with work-table position. Then, ignoring for the moment the effects of the " fine " control, for any given table position, a particular one of the wipers A0 . . . A9 will be in contact with the centre tap C5. If the selector 21 is moved so as to link with a wiper which is the desired number of increments above or below that wiper which is on the centre tap ; the resulting error voltage will cause the motor to run until the device S1 has moved the wiper which is linked to 21 to the centre tap position and so re-position the work-table. In a modification, Fig. 3a (not shown), the number of wipers A0 &c. is halved by connecting each one to the mid-point of a transformer winding, the contacts D0 &c. being connected to the two ends of such windings. An auxiliary primary winding common to all such windings provides the necessary balancing signal. In a further modification, Fig. 4 (not shown), the wipers A0 &c. are omitted and the selector 21 is directly moved over the tappings C0 &c. by the device S1 with the interposition of a differential so that the selector 21 can be separately moved to set the command signal. Fine control.-Voltages tapped off a second transformer winding T2 by selectors 22, 23, 24, 25 are divided in appropriate decimal ratios by transformers T3, T4 and added to the " coarse " signal obtained at selector 21. The selectors 22 ... 25 are arranged as in Specification 846,381. These signals are balanced by the output of a toroidal transformer 10 which is adjusted by the device S2 as the table 3 is moved. One revolution of the device S2 corresponds to one " coarse " increment of position. The output of transformer 10 is added or substracted from the output voltage of transformer T1 by coils 6, 7 and cores 4, 5 as m Specification 802,472. Specification 847,367 also is referred to.