Research On Multi-path Error Analysis And Correction For Time-of-Flight Cameras

The ranging camera based on Time-of-Flight(TOF)technology has the advantages of simple principle,strong anti-interference performance,and easy on-chip integration.It has increasingly become a hotspot to replace other 3D ranging technologies.However,due to its unique ranging principle and the influence of the external environment,there are various systematic and non-systematic errors in the data obtained by TOF cameras.This paper focuses on the ranging error caused by the unique multipath superposition effect in TOF cameras.Different error correction methods are designed from the aspects of modulation and demodulation scheme,optical structure design and post-data processing.The main contents are shown below:1.The ranging principle of TOF camera based on modulation and demodulation method is studied.Mathematical modeling is performed for three modulation and demodulation methods including cosine-cosine method,cosine-square wave method,and pseudo-random binary cross-correlation sequence.Next,the generation mechanism of multipath reflection error is analyzed and mathematically deduced from three aspects: internal multipath scattering,external strong multipath reflection,and external multipath scattering.Moreover,the respective error simulation experimental platforms are set up.2.Aiming at the internal multipath scattering error,we have studied from two aspects: direct error compensation and indirect scattered signal compensation.In terms of direct error compensation,three error surface fitting models including Hermit-Bezier,B-spline with additive weights and B-spline with multiplicative weights were constructed.Experimental comparison shows that all three error models reduce the average error to less than 10 mm.In terms of scattering signal compensation,an iterative compensation algorithm based on the ratio of intensity to its gradient is designed.Experiments show that the correction performance of the scattering error in the area with large light intensity contrast is significantly improved,and the distance error is reduced by up to 85%.3.Aiming at the external strong multipath reflection error,two multipath signal separation methods are designed based on the multi-frequency signal modulation and demodulation scheme.They are the coarse and fine sparse decomposition based on compressed sensing and the improved penalty function method based on the initial pseudo-random binary cross correlation sequence.Through experimental verification and comparative analysis,these two methods have improved the separation accuracy to mm level on the premise of ensuring rapid multipath separation.For the external multipath scattering error,this study designed a direct and global component separation scheme based on dual-source sinusoidal modulation to eliminate the multipath scattering error.Experiments show that this method can effectively reduce the direct and global light separation errors caused by light leakage from checkerboard lighting,and the average distance error is reduced to 7.4 mm.