Patent ID: 7366637

Claim:
A form measuring instrument comprising: a table on which a workpiece having a surface whose surface roughness is to be evaluated is placed; a roughness sensor for detecting a cross-sectional shape of the surface to be evaluated of the workpiece, placed on the table, and for outputting measurement data that includes information on the cross-sectional shape; a relative movement mechanism for relatively moving the table and the roughness sensor such that the position of the roughness sensor on the workpiece is relatively moved along the surface to be evaluated, and for outputting the amount of relative movement at a movement resolution Δθ as indexed-movement-amount information; a time sampler for sampling the measurement data output from the roughness sensor, at a constant time interval t s shorter than a time required for the relative movement mechanism to move the table and the roughness sensor by the movement resolution Δθ; and a data processing mechanism for converting the measurement data sampled at the constant time interval t s by the time sampler to measurement data having a fixed interval, the fixed interval being smaller than the movement resolution Δθ of the relative movement mechanism and being required for roughness evaluation, according to the indexed-movement-amount information output from the relative movement mechanism, and for evaluating the surface roughness of the surface to be evaluated of the workpiece according to the measurement data having the fixed interval.