Surface testing apparatus

Claim 1

APPARATUS FOR MEASURING OR INDICATING THE ROUGHNESS ORR UNDULATIONS OF A SURFACE, COMPRISING TWO TRACERS CONSTITUTED BY A STYLUS AND A ROUNDED SKID ADJACENTLY MOUNTED IN FIXED RELATIONSHIP ON A COMMON SUPPORTING ARM, A PICKUP BODY CARRYING A PIVOTAL MOUNTING FOR THE SUPPORTING ARM, MEANS FOR BIASING SAID ARM ABOUT SUCH PIVOTAL MOUNTING TO URGE THE TRACERS TOWARDS THE SURFACE UNDER TEST, CHANGEOVER MEANS OPERATIVELY CONNECTED TO SAID SUPPORTING ARM FOR EFFECTING A PREDETERMINED RELATIVE DISPLACEMENT BETWEEN THE PIVOTAL MOUNTING AND THE TEST SURFACE SO THAT EITHER THE STYLUS ONLY OR THE SKID ONLY IS CAUSED TO ENGAGE THE TEST SURFACE, MEANS FOR DRIVING THE PICKUP BODY TO CAUSE THE OPERATIVE TRACER TO TRAVERSE THE TEST SURFACE, WHEREBY BY OPERATION OF THE CHANGEOVER MEANS TO TWO TRACERS MAY BE CAUSED SUCCESSIVELY TO TRAVERSE THE TEST SURFACE RESPECTIVELY DURING SUCCESSIVE TRAVERSING DRIVES, DETECTING MEANS RESPONSIVE TO PIVOTAL MOVEMENT OF THE SUPPORTING ARM DURING TRAVERSING DUE TO THE WORKING MOVEMENTS OF THE STYLUS OR SKID IN A DIRECTION GENERALLY NORMAL TO THE TEST SURFACE, AND MEANS FOR COMPARING THE OUTPUT OF THE DETECTING MEANS DURING TRAVERSING OF THE STYLUS WITH THE OUTPUT OF SUCH DETECTING MEANS DURING TRAVERSING OF THE SKID, INCLUDING A DEVICE FOR TEMPORARILY STORING AT LEAST ONE OF SUCH OUTPUTS, TO PROVIDE A SIGNAL FOR OPERATING A MEASURING OR INDICATING INTRUMENT.