Control apparatus for a step drive

Control apparatus for a step drive assembly which includes a rotatable operating unit and a change-over clutch unit for selectively connecting said operating unit to a continuously running motor or a stationary brake, said change-over clutch unit having input stop and start lines;

• said control apparatus comprising, a disk connected to said operating unit for rotation therewith and having a circular track with first and second zones, sensor means scanning said zones and outputting a pulse train, an evaluating circuit responsive to said pulse train having a first time comparator circuit for outputting a positional stop signal and a second time comparator circuit for outputting an overload stop signal, said first and second comparator circuits having respective first and second limiting time values associated therewith, said first and second zones having alternating elements with the elements of said first zone being uniformly smaller than the elements of said second zone except that at least one signal element of said first zone is the largest of all said elements, said first time comparator circuit outputting said positional stop signal when said first limiting time value is between the nominal operating speed scanning times for said signal element and for the other elements of said first zone, said second time comparator circuit outputting said overload stop signal when said second limiting time value is larger than the combined nominal operating speed scanning times for adjacent elements of said first and second zones.