基于标定的任意半径柱面上2维条形码畸变校正

Restoration of distorted 2D barcode marked on arbitrary radius cylinder based on calibrated camera

目的 2维条形码在直接零件标识技术中应用越来越广泛,但对于标刻在柱形零件上的2维条形码,存在扭曲形变的问题。严重的扭曲形变将会改变2维条形码的本原模式,造成识读失效或困难,因此需要进行畸变校正以恢复其本原模式。该内容属于目标复原的主题范畴。方法为了校正这种畸变,首先分析了柱面2维条形码的畸变形成原理,然后基于标定的机器视觉装置与透视投影原理建立柱面上2维条形码畸变校正模型,最后在图像信息中推导出拟合椭圆与柱形零件的对应关系,通过拟合椭圆估计出柱形零件半径参数信息,并代入畸变校正模型得到最终的校正结果。结果实验选取两幅标刻在不同半径且采用不同视角获取的具有严重扭曲形变的2维条形码图像,根据预先标定好的机器视觉系统与该算法进行校正,实验结果表明,该方法能够有效地校正自由半径柱面上2维条形码的扭曲畸变,且算法时间控制在1 s之内。结论当前大多数已知文献仅研究标刻在平面上2维条形码的识别,而该方法扩展了2维条形码的应用范围,即不仅可以作为平面产品的标识,也可以作为柱面产品的标识。当然,根据本文提供的思路,可以将2维条形码的标识面范围扩展到任意已知曲面。

Objective In the field of direct part marking technology, 2D barcode is more and more widely used, but there is a problem that 2D barcodes marked on a cylindrical part have spatial distortions which will result in reading difficulties. Ex- isting algorithms mostly attempt to recognize 2D barcode marked on the plane which only have perspective and incline dis- tortion. However, they can hardly recognize 2D barcode marked on cylindrical part because the pattern of 2D barcode is changed by spatial distortion. For correcting this difficulty, a new method should be proposed to recovery the distorted 2D barcode, and the radius parameter of cylindrical part should be automatically got without manual measurement. Method We firstly analyze the principle of forming distorted 2D barcode marked on cylindrical parts, and we establish a spatially distort- ed 2D barcode correction model based on calibrated machine vision mechanism and the principle of perspective projection. then deduces the relationship between fitted ellipse and the radius of cylindrical part in the image, in addition, estimates the radius by the ellipse parameters, finally substitutes it into the correction model to get the corrected 2D barcode. In the experiment, we select two distorted 2D barcodes marked on the cylindrical parts with different radius parameter, and ac- quires pictures of them from different views. It gets fixed parameters of the machine vision device, based on that the spatial-ly distorted 2D barcode correction model could be established. Result The experiment results show that, the two distorted 2D barcodes are recovered well and the processing time is limited in 1 second. Compared with previous methods, this algo- rithm is more concise because of prior calibration and spatial distortion mode. Besides, this algorithm is more automated be- cause the radius parameter could be automatically got by the image. Conclusion Based on camera calibration, the method is effective for correcting spatially distorted 2D barcode marked on arbitrary radius cylinder. The method extends the applica- tion range of 2D barcode that not only flat part but also cylindrical part could also be identified. However, in the future work it should introduce nonlinear distortion of the lens and get the more accurate camera calibration parameters for more ideal restoration result.