Elimination of Gyro Rate Offset by Using a Rotating Mechanism for Large Scale Straightness Evaluation

Straightness evaluations by detecting tangential angles of the straightness are considered to be advantageous for evaluating large objects. Among them, a method using a gyro can be applied in a horizontal plane and has no limitation for its evaluation distance. However, even the most stable gyro has considerable fluctuation called a gyro rate offset in its angular signal and it becomes a dominant error source. We had demonstrated that the gyro rate offset can be eliminated by periodical reversal measurement by using a conventional fiber optic gyro (FOG) unit. Here, we adopted a rotating mechanism with a rotating rate up to several revolutions per second for performing faster reversal measurement in order to eliminate faster fluctuations in the gyro rate offset. Analysis and experiment show that the gyro rate offset can be derived and eliminated together with an alignment error of the gyro direction. Finally, we derive an angular signal to be detected for our straightness evaluation with a reasonable signal waveform.