Photosensitive polyphase apparatus for detecting and indicating the extent of relative movement

Claim 1

APPARATUS FOR DETECTING THE EXTENT OF RELATIVE MOVEMENT BETWEEN TWO RELATIVELY MOVABLE MEMBERS, COMPRISING: A POLYPHASE ALTERNATING CURRENT SOURCE FOR PROVIDING A REFERENCE SIGNAL; A PLURALITY OF SIGNAL PRODUCING MEANS EQUAL IN NUMBER TO THE NUMBER OF PHASES EACH PRODUCING A PERIODIC SIGNAL; MEANS FOR COMBINING SAID PERIODIC SIGNALS; PHASE DISPLACING MEANS COUPLED TO SAID SIGNAL PRODUCING MEANS FOR DISPLACING THE PHASE OF SAID COMBINED PERIODIC SIGNALS RELATIVE TO SAID REFERENCE SIGNAL BY AN AMOUNT PROPORTIONAL TO THE EXTENT OF ANY RELATIVE MOVEMENT BETWEEN THE TWO RELATIVELY MOVABLE MEMBERS, SAID PHASE DISPLACING MEANS INCLUDING FIRST AND SECOND CROSSED GRATINGS HAVING THE SAME NUMBER OF RULINGS PER UNIT LENGTH, THE FIRST GRATING BEING MOUNTED IN FIXED RELATION TO THE ONE RELATIVELY MOVABLE MEMBER, THE SECOND GRATING BEING MOUNTED IN FIXED RELATION TO THE OTHER SAID MEMBER, AND SAID GRATINGS BEING SUPERIMPOSED FOR PRODUCING A PATTERN OF INTERFERENCE FRINGES; SAID SIGNAL PRODUCING MEANS BEING POSITIONED SO AS TO RESPOND TO THE FRINGE PATTERN; AND RECEIVER MEANS COUPLED TO THE ALTERNATING CURRENT SOURCE AND TO SAID SIGNAL PRODUCING MEANS AND RESPONSIVE TO ANY PHASE DIFFERENCE BETWEEN SAID REFERENCE SIGNAL AND SAID COMBINED PERIODIC SIGNALS.