Fluid pressure operated sensing system

Claim 1

AN EDGE ALIGNMENT CONTROL SYSTEM COMPRISING (A) AN EDGE ALIGNMENT CONTROL MEANS FOR CONTROLLING THE POSITION OF A MOVING WEB OF MATERIAL AND CAPABLE OF ACTUATION IN RESPECTIVE OPPOSITE SENSES TO TEND TO MOVE THE WEB LATERALLY IN RESPECTIVE OPPOSITE DIRECTIONS, (B) AN EDGE POSITION SENSING HEAD HAVING FLUID PRESSURE OUTPUT MEANS FOR SENSING EDGE POSITION AND GENERATING FIRST, SECOND, THIRD AND FOURTH PRESSURE OUTPUTS INDICATIVE OF THE POSITION OF THE EDGE OF THE MOVING WEB, THE DIFFERENCE BETWEEN THE FIRST PRESSURE OUTPUT AND THE SECOND PRESSURE OUTPUT HAVING ONE VALUE WHEN THE WEB IS IN A CORRECT POSITION AND HAVING A SUBSTANTIALLY DIFFERENT VALUE WHEN THE WEB IS OFFSET FROM THE CORRECT POSITION IN ONE DIRECTION, THE DIFFERENCE BETWEEN THE THIRD PRESSURE OUTPUT AND THE FOURTH PRESSURE OUTPUT HAVING ONE VALUE WHEN THE WEB IS IN THE CORRECT POSITION AND HAVING A SUBSTANTIALLY DIFFERENT VALUE WHEN THE WEB IS OFFSET FROM THE CORRECT POSITION IN A DIRECTION OPPOSITE TO SAID ONE DIRECTION, (C) FIRST AND SECOND FLUID PRESSURE RESPONSIVE DEVICES COUPLED TO SAID FLUID PRESSURE OUTPUT MEANS OF SAID HEAD AND RESPONSIVE TO SAID FIRST AND SECOND PRESSURE OUTPUTS, AND TO SAID THIRD AND FOURTH PRESSURE OUTPUTS, RESPECTIVELY, TO PROVIDE RESPECTIVE FIRST AND SECOND MECHANICAL OUTPUTS, (D) FIRST AND SECOND MECHANICALLY ACTUATED SWITCHING DEVICES COUPLED RESPECTIVELY TO SAID FIRST AND SECOND FLUID PRESSURE RESPONSIVE DEVICES AND ACTUATED RESPECTIVELY BY SAID FIRST AND SECOND MECHANICAL OUTPUTS THEREFROM,