Control arrangement for causing track supported implement to remain in parallelism with itself

DETAILED DESCRIPTION What is claimed is: 1.
A control device for causing an implement such as a crane having laterally spaced wheeled carriages rollingly supported on respective laterally spaced tracks to remain in parallel with itself while moving along the tracks; said device comprising in combination; pick-up means on at least one carriage spaced longitudinally along the carriage and also spaced laterally from the respective track and each operable to develop a signal in conformity with lateral movement of the pertaining region of the carriage on the respective track as brought about by movement of said implement out of a position of parallelism with itself, a comparator connected to receive said pick-up signals and operable to develop a control signal in conformity with the difference therebetween, and control means connected to receive said control signal and operable in conformity with said control signal to apply corrective vertical axis influences on said implement tending to restore the implement to said condition of parallelism with itself.
2.
A control device in combination according to claim 1 in which each pick-up means comprises a magnetic core having a detector pole shoe opposed to each side of the rail and an exciting pole shoe opposed to the top of the rail, a pick-up coil on each detector pole shoe, and an exciting winding on said exciting pole shoe, said exciting winding when energized establishing respective magnetic fields through said detector pole shoes which vary differentially when the pick-up means and the respective track move relativley in the lateral direction.
3.
A control device in combination according to claim 2 in which each pick-up means comprises a pair of cores adjacent the side of the respective rail, a first coil on one core adapted for energization from an alternating current source, a second coil on the other core and oscillator circuit means in which said second coil is connected, said oscillator circuit developing a pick-up signal which varies in conformity with changes in spacing between said cores and said rail