Automatic level control system for construction machines

Claim 1

AN AUTOMATIC LEVEL CONTROL SYSTEM FOR CONSTRUCTION MACHINES OF THE TYPE HAVING A WORKING TOOL CARRIED UPON TRACTION MEANS BY VERTICALLY ADJUSTABLE SUPPORT MEANS, SAID CONTROL SYSTEM COMPRISING; A POWER MEANS FOR ACTUATING SAID SUPPORT MEANS, SAID POWER MEANS BEING RESPONSIVE TO A POWER MEANS INPUT QUANTITY AND BEING OPERATIVE TO PROVIDE A SUPPORT MEANS INPUT QUANTITY PROPORTIONAL IN SENSE AND MAGNITUDE TO SAID POWER MEANS INPUT QUANTITY; A SENSOR MEANS MOVABLE WITH SAID WORKING TOOL AND COOPERATIVELY ENGAGEABLE WITH AN EXTERNAL REFERENCE DISPOSED ALONG AND OUTSIDE THE PATH OF TRAVEL OF SAID CONSTRUCTION MACHINE, SAID SENSOR MEANS BEING RESPONSIVE TO THE DIFFERENCE BETWEEN THE ACTUAL HEIGHT OF SAID WORKING TOOL AND A SELECTED HEIGHT IN ACCORDANCE WITH SAID EXTERNAL REFERENCE LEVEL AND OPERATIVE TO PROVIDE A SENSOR MEANS OUTPUT QUANTITY PROPORTIONAL IN SENSE AND MAGNITUDE TO SAID DIFFERENCE IN HEIGHT; AND A TRANSDUCER MEANS RESPONSIVE TO SAID SENSOR MEANS OUTPUT QUANTITY AND OPERATIVE TO PROVIDE SAID POWER MEANS WITH AN INPUT QUANTITY WHICH IS PROPORTIONAL TO SAID SENSOR MEANS OUTPUT QUANTITY, SAID VERTICALLY ADJUSTABLE SUPPORT MEANS BEING MECHANICALLY MOVABLE, SAID SENSOR MEANS INCLUDING A MEMBER MECHANICALLY DISPLACEABLE IN RESPONSE TO A VARIATION IN HEIGHT OF SAID WORKING TOOL RELATIVE TO SAID EXTERNAL REFERENCE, AND SAID TRANSDUCER MEANS BEING OPERATIVE TO CONVERT THE DISPLACEMENT OF SAID DISPLACEABLE MEMBER TO A PROPORTIONAL ELECTRICAL SIGNAL DETERMINATIVE OF SAID POWER MEANS INPUT QUANTITY FOR CONTROLLING THE MOVEMENT OF SAID ADJUSTABLE SUPPORT MEANS.