Improvements in and relating to means for determining angular displacement

936,076. Control of A.C. motors. ASSOCIATED ELECTRICAL INDUSTRIES Ltd. Jan. 18, 1961 [Jan. 25, 1960], No. 2656/60. Class 38 (3). A feed motor in a machine tool is caused to rotate a predetermined amount by coupling to it a D.C. tacho-generator GN connected to a saturable reactor Tr arranged to stop the motor when saturation is reached. It is stated that this will occur due to the integration of the tacho-generator voltage with respect to time, and hence the feed motor will move a constant amount regardless of its speed. The amount may be regulated either by adjusting the output of the tacho-generator by a field rheostat EPOT or by connecting it to the reactor Tr via a potentiometer. Alternatively, or in addition, the reactor winding W1 may be tapped. Upon saturation of the reactor a relay I 1 is operated by the resultant increase in current through the winding W1, either directly or after amplification ; to increase sensitivity the relay may have a separately energized premagnetizing winding I 2 . The reactor is reset after each operation by an additional winding W2. An embodiment is described (Fig. 7, not shown) in which the feed motor is that of a planing machine and comprises a three-phase induction motor. This is energized at the beginning of each working stroke of the planer and operation of the relay disconnects the motor windings from the A.C. supply and connects them either to a source of D.C. or to capacitors for braking purposes. A push-button enables an operator to repeat the feed cycle. Specification 665,380 is referred to.