一种基于参数标定的投影条纹周期简易校正方法

基于三角测量原理的条纹投影轮廓测量系统中,倾斜投影到参考平面上的条纹将产生周期展宽现象,引起相位失真甚至影响测量精度。论文以条纹位置为控制变量推导出条纹周期校正的线性数学模型,通过简便的标定获得模型参数,由此反算出新的待投影条纹,并在参考平面上获得周期分布的投影条纹。实验结果表明校正后的条纹周期变化范围在±0.1像素内,并且该方法能够获得更为精确的三维轮廓测量结果。     

离焦条纹投影三维测量中正弦光栅的二值化方法研究

采用离焦二值条纹投影技术进行三维面形测量可以克服数字投影仪的非线性响应,同时有利于提高投影速度,实现高速测量.通过理论分析和实验研究了采用数字投影仪时二值条纹的基频、高次谐波能量分布与条纹周期的关系.结合相移算法,以相位测量误差为指标,衡量各种二值条纹的性能.研究结果表明:在周期小时,罗奇光栅和二维误差扩散算法生成的二值条纹离焦后能产生正弦性较好的条纹;在采用满周期等间隔奇数次相移时,罗奇光栅离焦能获得更高的测量准确度;在周期大时,采用优化脉宽调制方法得到的二值光栅离焦测量准确度最高.研究结果为离焦条纹投影三维测量中二值光栅的选择提供了依据.     

一种新的基于条纹投影的三维轮廓测量系统模型

提出一种新的光栅条纹投影轮廓测量术系统模型,新模型不要求测量系统满足光心连线平行于参考面、成像系统光轴垂直于参考面以及两光轴相交于参考面上等约束条件,只需投射至参考平面的正弦光栅条纹之间相互平行,简化了系统校准过程,有利于现场测量。得到的高度相位映射关系式中,待标定的系数与像点的坐标无关,不需要对每一个像点进行采样,能够减少系统标定所需的时间。实验表明:所提方法使投影装置和成像系统的位置校准过程简单,提高了系统标定的速度,且具有较高的测量精度,能够测量复杂面形的物体,增强了光栅投影三维测量系统的实用性。     

基于三维缺陷检测的DMD数字条纹投影光学系统设计

基于半导体行业中PCB焊膏印刷检测的实际应用,采用0.45 WXGA DMD芯片设计了数字条纹投影光学系统.以LED作为光源,结合透镜阵列照明DMD芯片;同时,为了减小投影三角关系造成的条纹周期不均匀性对检测结果的影响,采用双远心光路结构将DMD生成的条纹成像到待测表面,且适用的最小检测面积为1mm2.光学模拟结果表明,该数字投影系统在被投影表面上的照明均匀性为91%,投射条纹的对比度高于0.8,且条纹周期均匀,为实际应用与后续条纹分析提供了良好保障.     

基于彩色光栅投影的快速三维测量方法

 针对条纹投影术提取物体高度信息的问题,提出了一种新的基于彩色光栅投影的三维测量方法。对选取G分量为255,R,B分量各取0或255而组成的青、白、黄、绿四色遵循格雷码原理进行编码,然后将G分量作正弦调制形成投影光栅投向被测物体。提取采集到的光栅变形图中G分量,利用傅里叶变换方法得到其初始相位;同时对采集到图像中的R,B分量作阈值迭代分割而G分量自动赋值为255,综合三分量信息得到条纹颜色信息进而获取条纹的周期信息,从而展开相位。全过程仅需投影一幅彩色光栅图就能完成三维测量,实验结果表明该算法易于实现,在测量实时性和精确性上表现良好。     

全息光栅干涉条纹三维锁定系统的设计

全息曝光系统中干涉条纹的稳定性直接影响光栅掩模质量。研究了参考干涉条纹的特性,提出一种光栅相位、倾斜度和周期的检测方法。为提高光栅曝光系统的稳定性,设计了一套全息光栅干涉条纹三维锁定系统。利用摄像机对参考干涉条纹进行检测,利用微电机和压电陶瓷对光路进行微调,可实现对光栅相位、倾斜度和周期的有效控制。实验结果表明,三维锁定系统可有效提高干涉条纹的稳定性,缩短光栅曝光前的静台稳定时间,提高光栅曝光对比度,可为大口径全息光栅曝光质量的提高提供技术支持。     

一种弱化莫尔条纹的狭缝光栅屏裸眼3D显示器

常规竖直狭缝光栅和倾斜狭缝光栅的发光二极管(LED)屏裸眼3D显示器分别存在明显的莫尔条纹和立体图像串扰等问题,为此,提出一种弱化莫尔条纹的狭缝光栅LED屏裸眼3D显示器,它由LED屏和错位非均宽透光条的狭缝光栅构成。该狭缝光栅根据LED屏黑矩阵较宽的特点,通过适当增大透光条宽度和移动透光条在其周期中的位置,来增加狭缝光栅周期结构与LED屏像素周期结构之间的差异,降低莫尔条纹中暗带的对比度,并使莫尔条纹变得稀疏,从而达到既能弱化莫尔条纹,又不会明显增加立体图像串扰的目的。制作了所提狭缝光栅LED屏裸眼3D显示器样机,获得了莫尔条纹显著弱化、无明显立体图像串扰的显示效果,验证了理论的正确性。     

单周期条纹双四步相移投影仪的标定方法

针对投影仪标定方法中存在畸变及倾斜投影引起条纹周期、条纹级数变化的问题,提出一种单周期条纹双四步相移投影仪的标定方法.设计生成横向和纵向各两组单周期条纹图像,经投影仪投影到带有圆形标识的标定板上,相机同步采集标定板图像,叠加由双四步相移获得的两幅相位主值图,对叠加相位主值图相位展开,利用展开的绝对相位值计算投影仪像素坐标值,最终将投影仪标定转换为成熟的相机标定.实验结果表明:仿真投影仪标定实验准确度的最大重投影误差约为0.4pixel,均方根误差为0.132 96pixel;实际投影仪标定实验准确度的最大反投影误差约为0.46pixel,均方根误差为0.143 12pixel;实验结果与仿真结果的最大反投影误差相差15%,均方根误差相差7.6%.与现有的采用三频相位展开进行投影仪标定的方法相比,投影光栅图像数可减少8幅.该方法改善了现有投影仪标定方法的不足,标定准确度和标定效率均得到提高.     

高质量全息光栅的制作

全息光栅由感光版记录高斯光束干涉条纹制得 ,干涉条纹的不等宽性降低了光栅品质。制取高质量全息光栅的关键是要用均匀平面波作光源。在分析干涉区内光强分布的基础上 ,给出了制作等周期正弦全息光栅的两种方法 :限制曝光区大小的方法和高斯光束强度均匀化的方法。     

基于彩色编码光栅投影的双N步相移轮廓术

双N步相移轮廓术虽然可以大大降低由于光栅条纹的非正弦性所导致的相位误差,但增加了一倍的投影条纹数量,降低了测量效率。针对此问题,本文提出一种基于彩色编码光栅投影的双N步相移轮廓术,它将原相移条纹和附加相移条纹编码成双色条纹,融合到一幅彩色光栅条纹中投影,然后从采集的彩色条纹中提取两套条纹的相位信息,分别解包裹相位后,融合两包裹相位以减小相位误差。为验证所提方法的有效性,将该方法与两种典型的相位展开算法结合进行实验。实验结果证明,所提方法能有效降低相位误差,且不需要增加任何额外的光栅条纹,测量效率提高了46%。     

光学三维扫描仪光强传递函数的测量和校正

由于数字光栅投影仪的光强传递函数对于正弦投影条纹的质量以及相位测量精度起着至关重要的作用,本文提出了一种校正光学三维扫描仪光强传递函数的新方法。首先,分析了由于投影仪非线性响应引起的光栅谐波的相位测量误差;然后,通过投影一组不同灰度级的图像,并利用光功率计测出数字投影仪投出图像的亮度。接着,通过分析得到数字投影仪的非线性响应特性曲线,再经过数据处理,即可获得投影仪的光强传递函数;最后,对光强传递函数进行反函数逆变换,得到一个校正后的非正弦光栅,利用投影仪对该光栅的投影即可在被测物体表面上获得一个正弦光栅。数字投影仪对标准平板的测量结果表明,校正前平均误差为0.71 mm,校正后为0.55 mm;对于标准量块的测量,校正前的平均误差为0.62 mm,校正后为0.15 mm。上述结果表明,本文提出的方法可以减小由于系统非线性响应引起的测量误差并提高测量精度。     

光学三维传感实验设计

基于三角法测量原理设计了光学三维传感实验系统.实验系统光源采用数字光学投影仪,并用计算机生成电子光栅.将电子光栅投影到被测物或参考面后,使用CCD进行图像采集,并通过视频采集卡将采集的图像数据传到计算机中保存.通过相应算法对保存的数据进行考查、处理,最终得到解调后的三维信息.     

Period correction method for binary fringe defocused projection

Binary fringe defocused projection can resolve the problem caused by the nonlinear gamma of the projector. Owing to the intersecting axis measurement system, the broadening of the fringe period on the reference plane can cause measurement errors. Non-uniform periodical binary fringe defocused projection is utilized to overcome this problem. After appropriate defocused projection of non-uniform periodical binary fringe, uniform periodical sinusoidal fringe can be obtained on the reference plane. This method can prevent the nonlinear gamma effect and broadening of the fringe period, and filter high harmonics and high-frequency noise. Three-dimensional (3-D) shape measurement experiments of standard flat are performed with four-step phase-shift method. Experimental results demonstrate that the proposed method exhibits high measurement precision. Highly accurate 3-D measurements of large objects can also be performed with the proposed method.     

Single fringe projection profilometry based on sinusoidal intensity normalization and subpixel fitting

A novel fringe projection profilometry using a single sinusoidal fringe pattern projected is proposed. Computer-generated sinusoidal fringe and uniform intensity patterns are firstly projected on a testing object by a liquid crystal display projector. The variable reflection intensity of a fringe pattern is then roughly normalized by division operation applied to the grabbed fringe and uniform intensity patterns projected. Fringe intensity is further normalized by employing an interpolation algorithm. The deformed sinusoidal pattern encoding object shape is converted to a wrapped phase map without using phase-shifting or Fourier transform. Computer simulation and experimental performance are evaluated to demonstrate the validity of the proposed method. The experimental results compared with those of the four-step phase-shifting and fast Fourier transform methods are also presented.     

Compact compound-eye projector using superresolved projection

We propose a compact compound-eye projector using superresolved projection. The optics are composed of multiple small suboptics (units) to reduce their thickness in the projector. Each of the suboptics adds a subpixel shift to a projected image for superresolved projection and has a color filter or a dispersive element for multicolor projection. The projected images in the units are determined via a model of the system in preprocessing. The images are projected by the suboptics and superimposed on a screen. In this Letter, we describe the system model and show the simulation results.     

A novel fringe adaptation method for digital projector

Aimed to obtain high-quality sinusoidal fringe projection, a new method to correct the output fringe of digital projector is presented. The method is based on the proposed fringe transform model, which describes the relationship of the input and output fringe pattern. Firstly, a series of fringe patterns are projected and from the fringe images, the transform function is calculated by the pattern shifting method. At last, by modifying the input fringe pattern, a standard sinusoidal output fringe can be achieved. Different from the previous methods, the waveform nonlinearity is estimated by varying the intensity of the projected fringe pixel by pixel; thus the waveform nonlinearity can be estimated precisely and the time cost is considerably reduced. Experimental results show that by modification of the input projection patterns the projector can project fringe with high-quality sinusoidal waveform leading to high performance of the projection system.     

Flexible digital projector calibration method based on per-pixel distortion measurement and correction

When a digital projector is applied in high precision applications, the intrinsic parameters and distortion characteristics should be calibrated precisely. In this paper, a flexible full-field projector calibration method is proposed without any approximate distortion model. With planar homography theory and fringe projection technique, the projector distortion characteristic on each pixel can be measured independently and an initial distortion map is generated. The intrinsic parameters are calibrated afterwards. Then, the initial distortion map can be refined by correcting the non-perpendicularity between the optical axis and image plane. The original pattern to be projected is corrected with the refined distortion map. Thus, the calibrated projector can be regarded as an ideal projector conforming to the pinhole model. Experimental results show a nearly ideal residual map for the corrected projection pattern. In addition, the proposed calibration method is flexible without any sophisticated ancillary equipment or complicated procedure.     

点阵绝对相位彩色多频光栅傅里叶变换轮廓术

提出一种将三角法测距与多频光栅相结合的方法,充分利用数字投影的RGB通道,将多频光栅与点阵同时投影在物体表面,综合控制受高度调制的相位信息的提取,最终获取物体的三维形貌。仿真结果显示,在高度跳变使高频光栅位移达102量级个周期时,可以准确还原原始形貌。通过实验验证,本方法能够同时复原169mm的陡峭高度跳变以及3mm的微小细节,提高了传统双频光栅的性能,具有处理较大截断面和保证细节部分的测量能力,较好地改善了傅里叶变换轮廓术(FTP)的应用性能。