Accuracy testing device

Claim 1

A testing device for tsting the setting accuracy of a machine by measuring the spacing of a first machine locus with respect to a second machine locus at at least two points on a circular arc, comprising a first, ball-ended reference element adapted to be fixed to one part of the machine with the center of the ball representing the first locus, a second, ball-ended reference element adapted to be fixed to another part of the machine with the center of the ball representing the second locus, interconnecting means for interconnecting said ball ends of the reference elements in respective mountings and permitting relative rotation of the ball ends with respect to said interconnecting means, the mounting of said respective mountings for said first element ball end permitting relative movement of said first element ball end and said interconnecting means, and the mounting of said respective mountings for said second element ball end being at a fixed position on said interconnecting means, a single axis transducer for directly sensing the surface of said ball end of said first reference element to detect displacement thereof relative to said second reference element, and computing means for calculating from the output of said transducer the deviation from a precise arcuate path of the first locus.