Development of a high-precision straightness measuring system with DVD pick-up head

A low-cost and high-precision straightness measurement system using a DVD pick-up head has been developed in this research. By removing its objective lens the pick-up head of a commercial DVD player possesses excellent properties of stable laser power, collimated laser beam, circular Gaussian distribution and sensitive photodetectors. A moving knife-edge piece is placed between the pick-up head and a plane mirror. According to the knife-edge principle, the non-shaded part of the laser beam will be reflected back and focused onto the four-quadrant photodetector of the pick-up head. The four-quadrant signals are added to measure the returned laser power. Theoretical analysis based on the circular Gaussian distribution theory and regression method can attain the straightness error of the knife-edge while it moves along the beam direction. This low-cost system can apply to the straightness measurement of precision coordinate measuring machines and NC machine tools. Experimental results showed the achieved accuracy is better than ±0.2 µm within the measuring range of 200 µm.