The accuracy of solid density primary standard is decided mainly by the accuracy of the diameter measurement of silicon sphere. With traditional five-interferogram algorithm to unwrap phase for di- ameter measurement,...The accuracy of solid density primary standard is decided mainly by the accuracy of the diameter measurement of silicon sphere. With traditional five-interferogram algorithm to unwrap phase for di- ameter measurement, the phase steps should be equal to π/2 exactly, but this is almost impossible to achieve in nanometer positioning technique. In order to overcome this defect, we have derived an im- proved five-interferogram algorithm, which not only keeps the high accuracy of traditional five-inter- ferogram algorithm, but also does not require absolute equal step to unwrap phase. Instead, the im- proved five-interferogram algorithm only needs measuring phase shifting. Based on the improved al- gorithm, we have developed a novel interferometer with special etalon, and the cavity length of this etalon can be changed by pressure from vertical direction to realize phase shifting. The accuracy of this interferometer is better than 3 nm and can be improved in future research.展开更多
Digital structured light （SL） profilometry is increasingly used in three-dimensional （3D） measurement technology. However, the nonlinearity of the off-the-shelf projectors and cameras seriously reduces the measure...Digital structured light （SL） profilometry is increasingly used in three-dimensional （3D） measurement technology. However, the nonlinearity of the off-the-shelf projectors and cameras seriously reduces the measurement accuracy. In this paper, first, we review the nonlinear effects of the projector-camera system in the phase-shifting structured light depth measurement method. We show that high order harmonic wave components lead to phase error in the phase-shifting method. Then a practical method based on frequency domain filtering is proposed for nonlinear error reduction. By using this method, the nonlinear calibration of the SL system is not required. Moreover, both the nonlinear effects of the projector and the camera can be effectively reduced. The simulations and experiments have verified our nonlinear correction method.展开更多
文摘The accuracy of solid density primary standard is decided mainly by the accuracy of the diameter measurement of silicon sphere. With traditional five-interferogram algorithm to unwrap phase for di- ameter measurement, the phase steps should be equal to π/2 exactly, but this is almost impossible to achieve in nanometer positioning technique. In order to overcome this defect, we have derived an im- proved five-interferogram algorithm, which not only keeps the high accuracy of traditional five-inter- ferogram algorithm, but also does not require absolute equal step to unwrap phase. Instead, the im- proved five-interferogram algorithm only needs measuring phase shifting. Based on the improved al- gorithm, we have developed a novel interferometer with special etalon, and the cavity length of this etalon can be changed by pressure from vertical direction to realize phase shifting. The accuracy of this interferometer is better than 3 nm and can be improved in future research.
基金Project supported by the Science and Technology Major Projects of Zhejiang Province,China(Grant No.2013C03043-5)
文摘Digital structured light （SL） profilometry is increasingly used in three-dimensional （3D） measurement technology. However, the nonlinearity of the off-the-shelf projectors and cameras seriously reduces the measurement accuracy. In this paper, first, we review the nonlinear effects of the projector-camera system in the phase-shifting structured light depth measurement method. We show that high order harmonic wave components lead to phase error in the phase-shifting method. Then a practical method based on frequency domain filtering is proposed for nonlinear error reduction. By using this method, the nonlinear calibration of the SL system is not required. Moreover, both the nonlinear effects of the projector and the camera can be effectively reduced. The simulations and experiments have verified our nonlinear correction method.
