Wavefront measurement of a multilens optical system based on phase measuring deflectometry

Usually,a multilens optical system is composed of multiple undetectable sublenses.Wavefront of a multilens optical system cannot be measured when classical transmitted phase measuring deflectometry[PMD] is used.In this study,a wavefront measuring method for an optical system with multiple optics is presented based on PMD.A paraxial plane is used to represent the test multilens optical system.We introduce the calibration strategy and mathematical deduction of gradient equations.Systematic errors are suppressed with an N-rotation test.Simulations have been performed to demonstrate our method.The results showing the use of our method in multilens optical systems,such as the collimator and single-lens reflex camera lenses show that the measurement accuracy is comparable with those of interferometric tests.

High-speed and high-efficiency three-dimensional shape measurement based on Gray-coded light

Fringe projection profilometry has been increasingly sought and applied in dynamic three dimensional(3D)shape measurement.In this work,a robust,high-efficiency 3D measurement based on Gray-coded light is proposed.Unlike the traditional method,a tripartite phase unwrapping method is proposed to avoid the jump errors on the boundary of code words,which are mainly caused by the defocusing of the projector and the motion of the tested object.Subsequently,the time overlapping coding strategy is presented to greatly increase the coding ef-ficiency,decreasing the projected number in each group from seven(i.e.,3+4)to four(i.e.,3+1)for one restored 3D frame.The combination of two proposed techniques allows the reconstruction of a pixel-wise and unambiguous 3D geometry of dynamic scenes with strong noise using every four projected patterns.To the best of our knowledge,the presented techniques for the first time preserve the high anti-noise ability of a method based on the Gray code while overcoming the drawbacks of jump errors and low coding efficiency.Experiments have demonstrated that the proposed method can achieve robust,high efficiency 3D shape measurement of high speed dynamic scenes even polluted by strong noise.

Generic nonlinear error compensation algorithm for phase measuring profilometry

In this Letter,the periodical errors,which are caused by the nonlinear effect of the commercial projector and camera,are analyzed as a more generic single-coefficient model.The probability density function of the wrapped phase distributions is used as a tool to find the compensation coefficient.When the compensation coefficient is detected,on the premise of ensuring accuracy,a correlation algorithm process is used to replace the traditional iterative process.Therefore,the proposed algorithm improves the efficiency of coefficient detection dramatically.Both computer simulation and experiment show the effectiveness of this method.

Superfast and large-depth-range sinusoidal fringe generation for multi-dimensional information sensing

Among many multi-dimensional information sensing methods such as structured-light and single-pixel imaging technologies, sinusoidal fringe generation is general and crucial. Current methods of sinusoidal fringe generation force concessions in either the speed or the depth range. To mitigate this trade-off, we have simultaneously achieved both speed breakthrough and depth range enhancement by improving both the optical projection system and binary coding algorithm based on an off-the-shelf projector. Specifically, we propose a multifocal projection system and oblique projection method, which essentially eliminates the existence of a single focal plane in the conventional axisymmetric system and utilizes its anisotropy characteristics to achieve a superior filtering effect. Furthermore, the optimal pulse width modulation technique is introduced to modulate the square binary pattern for eliminating specific harmonics. To the best of our knowledge, the proposed method, for the first time,simultaneously achieved superfast(9524 frames per second) and large-depth-range(560 mm, about three times that of the conventional method) sinusoidal fringe generation with consistently high accuracy. Experimental results demonstrate the superior performance of the proposed method in multi-dimensional information sensing such as 3D, 4D, and [x, y, z, t;s(strain)].

Dual-frequency fringe for improving measurement accuracy of three-dimensional shape measurement

A new phase unwrapping method based on dual-frequency fringe is proposed to improve both high accuracy and large measurement range of three-dimensional shape measurement by synthesizing the projected dual-frequency fringes obtaining higher and lower frequencies.The lower-frequency one is their phase difference,which can help unwrap the wrapped phase of the higher-frequency one from their phase sum.In addition,the relationship between the measuring accuracy and the frequencies of the projected fringes is studied to guide the frequency selection in actual measurement.It is found that the closer the two frequencies are,the higher the measurement accuracy will be.The computer simulation and experiment results show the viability of this method.