Research On Three-dimensional Measurement System Based On Fringe Projection Technology With LED Arrays

With merits of non-contact,high speed and high accuracy,fringe projection technique has been widely used in fields like industrial inspection,reverse engineering,medical researches etc.,and has become one of the research focuses in the three-dimensional measurement area.Normally,a digital projector is used to project sinusoidal fringes in devices applying fringe projection technique.However,digital projectors have limits in projecting rates,their large sizes also hinder the system miniaturization.Furthermore,digital projectors have non-linear gamma distortions,which change as operating time increases.All these problems make digital projectors less satisfied to meet the emerging demands of systems with compact structures,high speed and low costs.To deal with issues mentioned above,in this thesis,based on three-step phase-shifting method,a three-dimensional measurement system was established,where phaseshifted fringes were produced by LED arrays and a grating.In this thesis,firstly,system parameters were selected based on the principle of phaseshifted fringes generation.Phase shift errors caused by parameter errors were analyzed,as well as relationships between system parameters and measurement range.Then,system hardwares were designed and selected.The system was built,projection experiments were carried,whose results indicated this system had the ability to project three-step phase-shifting fringes.In order to minimize phase-solving errors caused by ununified phase-shifts,an irritation algorithm was applied.To deal with error-passing phenomenon in shadow regions,an unwrapping algorithm united the line-scanning method and a binary mask was proposed.The result comparison with traditional unwrapping methods suggested that this method could lighten the influence caused by shadows.Finally,the relationships between system parameters and measurement errors were analyzed,several objects with different shapes were measured and reconstructed.Measurement results showed,with reference plane placed at a position of 130 mm,when projecting with Ronchi grating of 0.05 mm,the error was less than 0.05mm;when projecting with area modulation grating of 4mm,the maximum error was 0.121 mm.