A laser straightness measurement system using optical fiber and modulation techniques

Abstract In this paper a laser straightness measurement system is proposed. Using the characteristics of travelling straight and parallel, a new diode laser system utilizing optical fiber and modulation techniques was developed. This optically aligned beam is used to establish a reference line for the straightness measurement of any mechanical system. A four-quadrant photo detector was used to receive the laser beam. A phase sensitive detecting technique was adopted to process the opto-electrical signals from the detector. A single board microcomputer employing an 8098 processor was developed to conduct all data acquisition and signal processing. The influence from disturbing lights, circuit drift and beam drift can be removed from the system. The system was calibrated using an HP5528 laser interferometer. Results showed good accuracy of 0.3 μm within the range of ±100 μm and pointing stability of 0.3 μm at a 1 m distance was obtained. Two practical testing examples are carried out on a CMM and a grinding machine, respectively. Repeatability of both tests was found within 0.5 μm. This low-cost system has been successfully applied to the straightness measurement of a precision CMM.