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The structured light measurement method uses the principle that the fringe modulation information is sensitive to the object height information to realize the mapping from the fringe modulation information to the height information, which can be utilized to restore the three-dimensional shape of the object, smooth and rough surfaces. This method has a simple measurement system and belongs to coaxial measurement, which is considered a highly promising measurement method and has good application prospects in the field of aircraft surface shape measurement, surface defects detecting, etc. In most SIM, two essential parameters need to be accurately obtained to restore the 3D shape of the object which are the focus position of each pixel and the scan step. For years, researchers have constantly improved the structure of SIM system to obtain more accurate focus position to realize optimized measurement results. Meanwhile, the preset value of the scan step is directly substituted into calculation. However, the actual value of the scan step is very likely inconsistent with the preset value due to various factors in practical such as nonlinear motion of scan actuator, which will introduce great error into the measurement result. However, in the current structured light measurement methods, there is no solution to the problem of errors caused by the scanning system, which limits the further improvement of measurement accuracy and repeatability. In this paper, a random scanning error suppression method is proposed to solve this problem. The principle of mutual calibration of the second order slope of the theoretical modulation curve and the second order slope of the actual modulation curve of the grating fringe is used to achieve the accurate value of the scan step. Theoretical analysis and simulation are carried out to verify the feasibility of the proposed method.
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