Electrical-optical coordinate inspection machines

Claim 1

A probe structure for a coordinate inspection machine, the structure including a. a shaft rotatable about its own axis and carrying a radial arm, b. a probe extending generally parallel to that axis from a supporting carriage which is arranged to traverse the arm from a datum position of the probe, c. linear transducer means for measuring by a pulse count the extent and sense of the probe movement along the arm with respect to the datum position, d. control means for defining a system of rectangular X- and Ycoordinates in a plane normal to said axis with the axis as origin and for deriving with respect to that system (i) axis-engagement signals accurately responsive each time the probe comes into engagement with a said coordinate axis during a rotation of the shaft, and (ii) axis-identifying signals for severally representing the identity and sign of each coordinate axis thus engaged by the probe, e. bidirectional counters allocated to the X- and to the Ycoordinate axes of said system, and f. a logical network, controllable by said signals (i) and (ii) as the probe traces out a circle whilst the shaft rotates, for applying the transducer pulses to the X- and to the Y-counters throughout arcs of said circle having as the chords the X- and the Y-coordinate axes respectively, whereby at the conclusion of a complete rotation of the shaft the counters define by the number and sign of their contents the respective coordinates of the center of said circle with respect to said coordinate system.