Slope and grade control for paving machines

Claim 1

A CONTROL SYSTEM FOR A PAVING MACHINE THAT IS MOVABLE FORWARDLY OVER A BASE AND THAT COMPRISES A TRANSVERSE SCREED, MEANS FOR DEPOSITING PAVING MATERIAL ADJACENT THE LEADING EDGE OF THE SCREED TO FORM A MAT ON WHICH THE SCREED RIDES, AND SETTING MEANS ACTUABLE TO DIFFERENTIALLY ADJUST THE ANGLES OF ATTACK OF THE RESPECTIVE END PORTIONS OF THE SCREED TO VARY THE SCREED TWIST AND THEREBY TO CAUSE A CORRESPONDING PROGRESSIVE VARIATION IN TRANSVERSE SLOPE OF THE MAT SURFACE AS THE MACHINE MOVES FORWARD; SAID CONTROL SYSTEM BEING ADAPTED TO MAINTAIN A DESIRED VALUE OF THE TRANSVERSE MAT SLOPE AND COMPRISING IN COMBINATION SIGNAL MEANS OPERATIVELY CONNECTED TO THE SCREED FOR RESPONSE TO THE SCREED TWIST AND ACTING TO PRODUCE A SIGNAL HAVING A PREDETERMINED RELATIONSHIP TO SCREED TWIST, SERVO MEANS OPERATIVELY CONNECTED TO AND CONTROLLED BY SAID SIGNAL MEANS FOR DRIVING THE SCREED SETTING MEANS UNDER CONTROL OF THE SIGNAL TO MAINTAIN AN EQUILIBRIUM VALUE OF SCREED TWIST IN ACCORDANCE WITH SAID RELATIONSHIP INDEPENDENTLY OF IRREGULARITIES IN THE BASE, SAID SERVO MEANS INCLUDING TRIMMING MEANS OPERATIVELY ASSOCIATED WITH SAID SIGNAL MEANS AND ACTUABLE SELECTIVELY IN OPPOSITE DIRECTIONS TO MODIFY THE EQUILIBRIUM VALUE OF SCREED TWIST THAT IS MAINTAINED, SENSING MEANS RESPONSIVE TO DEVIATION OF THE TRANSVERSE SLOPE OF THE MAT SURFACE FROM THE DESIRED VALUE, AND MONITORING MEANS OPERABLY CONNECTED TO SAID TRIMMING MEANS AND SENSING MEANS FOR ACTUATING THE TRIMMING MEANS UNDER CONTROL OF THE SENSING MEANS IN A DIRECTION TO REDUCE SAID SLOPE DEVIATION.