A method for correcting non-linear errors in fringe projection 3D measurement

Abstract

The invention discloses a non-linear error correction method for three-dimensional fringe projection measurement, comprising: step S1: building a three-dimensional fringe projection measurement system, and a projector, a camera, and a measured object form a triangulation relationship; step S2: the projector in turn Project N color fringe patterns to the surface of the measured object; step S3: the camera collects the modulated color fringe image of the measured object; assuming that ideally, the color fringes are expressed as I n (x, y); Under the influence of non-linear and non-color crosstalk, the colored stripes are expressed as I′ n (x, y); Under the influence of nonlinear color crosstalk, the colored stripes are expressed as I″ n (x, y); Step S4: By setting an appropriate weighting coefficient α, calculate the red channel stripe I" under the influence of nonlinear color crosstalk n,r (x,y) and blue channel stripe I″ n,b (x,y) weighted fringes I″ n,a (x, y); Step S5: Calculate the weighted fringe I″ using N-step phase shift algorithm n,a Actual phase distribution φ″ of (x,y) a (x,y); since the weighted stripe I" n,a The amplitude of the 2nd harmonic of (x,y) is zero, making its actual phase distribution φ″ a (x,y) nonlinear error Δφ″ a (x,y) is greatly reduced.

Description

technical field [0001] The invention belongs to the technical field of three-dimensional measurement, in particular, the invention relates to a non-linear error correction method for three-dimensional measurement of fringe projection. Background technique [0002] The fringe projection three-dimensional measurement has the advantages of non-contact, high precision, and fast speed, and has been widely used in various fields, such as industrial inspection, reverse engineering, virtual reality, etc. However, the Gamma nonlinearity of the fringe projection system will distort the phase-shifted fringe image, and the phase distribution calculated from it has periodic errors, which in turn leads to 3D measurement errors. [0003] Because the nonlinear error period of the N-step phase shift method is N times the corresponding fringe period, some scholars calculate two phases with a π / N phase shift by the double N-step phase shift method, and calculate the average phase to compensate...

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Problems solved by technology

However, the gamma nonlinearity of the fringe projection system will distort the phase-shifted fringe image, and the phase distribution calculated from it has periodic errors, which in turn leads to 3D measurement errors

[0003] Because the nonlinear error period of the N-step phase shift method is N times the corresponding fringe period, some scholars calculate two phases with a π / N phase shift by the double N-step phase shift method, and calculate the average phase to compensate for the nonlinearity error, but this method needs to collect 2N fringe images and calculate the average phase of the two phases, which affects the measurement speed of the fringe projection system

[0004] In addition, some scholars generate another set of phase-shifted fringes by performing Hilbert transform on the N-step phase-shifted fringes, and calculate the average phase of the two sets of phase-shifted fringes to correct the nonlinear error, but this method involves frequency-domain operations. The amount is too large, the robustness is average

[0005] In addition, some scholars use the pre-calibration process, such as establishing a phase-error mapping table, estimating the Gamma value, etc. to correct the nonlinear error, but this kind of method needs to calibrate the system in advance, and the flexibility is poor.

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