Control apparatus for positioning an object

Claim 1

MEASURING APPARATUS RESPONSIVE TO THE MOVEMENT OF AN OBJECT RELATIVE TO A REFERENCE STRUCTURE INCLUDING MEANS FOR PRODUCING A REFERENCE CYLIC OPTICAL PATTERN, A FIRST OPTICAL GRATING SECURED TO SAID OBJECT, A SECOND OPTICAL GRATING IN OPTICAL REGISTRATION WITH AND MOVABLE WITH RESPECT TO THE FIRST GRATING, THE GRATINGS BEING RULED SO AS TO SET UP IN COMBINATION WITH ONE ANOTHER A CONTROL CYCLIC OPTICAL PATTERN WHICH IS SIMILAR TO SAID REFERENCE PATTERN AND WHICH IS DISPLACEABLE IN PHASE RELATIVE THERETO IN DEPENDENCE ON THE MOVEMENT OF THE OBJECT RELATIVE TO THE REFERENCE STRUCTURE, A LIGHT SOURCE FOR IRRADIATING SAID PATTERNS, CONTROL AND REFERENCE PHOTOCELL DEVICES SO DISPOSED AS TO BE IRRADIATED BY LIGHT FROM THE IRRADIATED CONTROL AND REFERENCE PATTERNS, RESPECTIVELY, MEANS FOR CAUSING THE OUTPUT SIGNALS FROM THE PHOTECELL DEVICES TO ALTERNATE AT A PREDETERMINED FREQUENCY, WITH A RELATIVE PHASE DISPLACEMENT EQUAL TO THAT OF THE PATTERNS, AND UTILISATION EQUIPMENT RESPONSIVE TO THE RELATIVE PHASE DISPLACEMENT OF THE ALTERNATING OUTPUT SIGNALS FROM THE PHOTOCELL DEVICES.