COHMAS Laboratory, Physical Sciences and Engineering Division (PSE), King Abdullah University of Science and Technology (KAUST), Thuwal 23955-6900, Saudi Arabia.
Sensors (Basel). 2019 Feb 10;19(3):719. doi: 10.3390/s19030719.
The stereo-digital image correlation technique using two synchronized industrial-grade cameras has been extensively used for full-field 3D shape, displacement and deformation measurements. However, its use in resource-limited institutions and field settings is inhibited by the need for relatively expensive, bulky and complicated experimental set-ups. To mitigate this problem, we established a cost-effective and ultra-portable smartphone-based stereo-digital image correlation system, which only uses a smartphone and an optical attachment. This optical attachment is composed of four planar mirrors and a 3D-printed mirror support, and can split the incoming scene into two sub-images, simulating a stereovision system using two virtual smartphones. Although such a mirror-based system has already been used for stereo-image correlation, this is the first time it has been combined with a commercial smartphone. This publication explores the potential and limitations of such a configuration. We first verified the effectiveness and accuracy of this system in 3D shape and displacement measurement through shape measurement and in-plane and out-of-plane translation tests. Severe thermal-induced virtual strains (up to 15,000 με) were found in the measured results due to the smartphone heating. The mechanism for the generation of the temperature-dependent errors in this system was clearly and reasonably explained. After a simple preheating process, the smartphone-based system was demonstrated to be accurate in measuring the strain on the surface of a loaded composite specimen, with comparable accuracy to a strain gauge. Measurements of 3D deformation are illustrated by tracking the deformation on the surface of a deflating ball. This cost-effective and ultra-portable smartphone-based system not only greatly decreases the hardware investment in the system construction, but also increases convenience and efficiency of 3D deformation measurements, thus demonstrating a large potential in resource-limited and field settings.
立体数字相关技术使用两个同步的工业级相机，广泛用于全场三维形状、位移和变形测量。然而，由于需要相对昂贵、庞大和复杂的实验装置，其在资源有限的机构和现场环境中的应用受到限制。为了解决这个问题，我们建立了一个具有成本效益和超便携的基于智能手机的立体数字相关系统，该系统仅使用智能手机和一个光学附件。该光学附件由四个平面反射镜和一个 3D 打印的反射镜支架组成，可以将入射场景分成两个子图像，模拟使用两个虚拟智能手机的立体视觉系统。虽然这种基于镜子的系统已经用于立体图像相关，但这是第一次将其与商业智能手机结合使用。本出版物探讨了这种配置的潜力和局限性。我们首先通过形状测量和平面内和平面外平移测试验证了该系统在三维形状和位移测量中的有效性和准确性。由于智能手机加热，在测量结果中发现了严重的热诱导虚拟应变（高达 15000 με）。该系统中温度相关误差产生的机制得到了清晰和合理的解释。经过简单的预热过程，基于智能手机的系统被证明可以准确测量加载复合材料试件表面的应变，其准确性可与应变计相媲美。通过跟踪泄气球表面的变形，演示了 3D 变形的测量。这种具有成本效益和超便携的基于智能手机的系统不仅大大降低了系统构建的硬件投资，而且提高了 3D 变形测量的便利性和效率，因此在资源有限和现场环境中具有很大的潜力。
