Patent ID: 7752003

Claim:
A method of measuring the length of a workpiece feature with a coordinate measuring machine, the coordinate measuring machine comprising a table, first and second guideways associated with the table, a bridge movable in a y-direction, a drive element associated with the first guideway for driving the bridge, a carriage movable on the bridge in an x-direction, a probe mounted to the carriage, and a first scale operative to permit scale readings indicating x-direction positions of the carriage along the bridge, the method comprising: (A) obtaining hysteresis error data for the bridge; (B) moving the bridge in a first direction, moving the carriage in a second direction, and, at a first bridge position and a first carriage x-direction position, taking a first reading from the first scale; (C) moving the bridge in a third direction opposite to the first direction, moving the carriage in a fourth direction, and, at a second bridge position and a second carriage x-direction position, taking a second reading from the first scale; and (D) determining a value of the length of the workpiece feature based on at least: the first reading from the first scale; the second reading from the first scale; the first direction of movement of the bridge; and the hysteresis error data; and calculating the difference between the first reading from the first scale and the second reading from the first scale to determine an unadjusted value of the x-component measurement of the workpiece feature; and adjusting the unadjusted value of the x-component measurement of the workpiece feature to account for hysteresis error, wherein adjusting the unadjusted value comprises computing 2*(R yz *Y z-rail — offset +Y probe — offset )), where R yz is the rotation of the bridge in radians, Y probe — offset is a y-direction distance of the probe from a vertically-movable ram, and Y z-rail — offset is a y-direction distance of the vertically-movable ram from a reference.