Thickness control servosystem

Claim 1

CONTROL APPARATUS COMPRISING A TRANSDUCER MEMBER ADAPTED TO PROVIDE A SIGNAL IN ACCORDANCE WITH CHANGES IN A VARIABLE TO BE CONTROLLED; A CONTROL ELEMENT ADAPTED TO EFFECT CHANGES IN SAID VARIABLE IN RESPONSE TO A CORRECTION SIGNAL; MEANS PROVIDING A SIGNAL INDICATIVE OF THE POSITION OF SAID CONTROL ELEMENT; MEMORY MEANS ADAPTED TO PROVIDE AS AN OUTPUT THE SAID POSITION INDICATIVE SIGNAL AFTER A PREDETERMINED TIME LAPSE, SAID PREDETERMINED TIME LAPSE HAVING A DURATION IN EXCESS OF ANY TIME DELAY BETWEEN OPERATION OF SAID CONTROL ELEMENT UPON SAID VARIABLE TO BE CONTROLLED AND THE SENSING OF THE EFFECT OF SAID OPERATION AT SAID TRANSDUCER ELEMENT; MEANS FOR PROVIDING A CORRECTION SIGNAL TO SAID CONTROL ELEMENT ADAPTED TO PROVIDE AS A CORRECTION SIGNAL THE SUM OF SAID POSITION INDICATIVE SIGNAL AND SAID TRANSDUCER SIGNAL LESS SAID MEMORY SIGNAL; MEANS FOR INHIBITING APPLICATION OF SAID CORRECTION SIGNAL TO SAID CONTROL ELEMENT UNLESS SAID CORRECTION SIGNAL EXCEEDS A PREDETERMINED VALUE FOR A PREDETERMINED TIME.