Patent ID: 7684057

Claim:
A linear measurement apparatus comprising: a frame which can be disposed around a measured object; a measuring unit comprising at least one pair of noncontact distance measuring sensors supported at the frame, the pair of noncontact distance measuring sensors comprising a first noncontact distance measuring sensor and a second noncontact distance measuring sensor, each sensor emitting light, receiving the light reflected from a measured object, and generating a signal corresponding to a distance from the corresponding sensor to the measured object, the first and second sensors being aligned on opposite sides of the measured object within the frame, the first sensor measuring a first gap distance between the first sensor and a first object position on the measured object in a first measurement line, the second sensor measuring a second gap distance between the second sensor and a second object position on the measured object in a second measurement line parallel to or identical to the first measurement line, the measuring unit measuring a plurality of first gap distances to a plurality of first object positions in a plurality of parallel first measurement lines and a plurality of second gap distances to a plurality of second object positions in a plurality of parallel second measurement lines lying on a plane identical to that in which the first measurement lines lie; a reference light emitter located at the frame for irradiating reference light onto the measured object in order to facilitate deployment of the linear measurement apparatus with respect to a reference position of the measured object; a distance calculator for calculating a plurality of candidate object lengths on the basis of the plurality of first and second gap distances, each candidate object length being a distance between one of the first object positions and one of the second object positions; and a maximum selector for selecting a maximum object length from among the plurality of candidate object lengths.