基于多芯光纤的高精度三维姿态测量关键技术研究

Three-dimension (3D) shape sensing plays an important role in the fields of minimally-invasive surgical instruments tracking, aircraft fatigue damage early warning, and tethered-robot motion trace controlling. The positioning accuracy, precision track reconstruction, and the capacity of the real-time monitoring are the key parameters in 3D shape sensing. Fiber optical sensing offers a number of advantages over conventional sensors, including the absence of electromagnetic interference, multiplexing capability, fast response, and high sensitivity. Owing to these intrinsic characteristics, fiber optical sensing is particularly well suited for measuring 3D shape. However, the accuracy of the tip positioning and track reconstruction is still limited to the centimeter level, which is far less than the requirements of minimally invasive medical and intelligent structure monitoring. Multi-core fiber holds unique capacity of multiple dimension, multiple parameter, and distributed sensing, which can provide support for the establishment of track vector space. Therefore, linking the research background of the applicant and group in the fields of multi-core fiber devices and distributed sensing technology, this project aims to develop a high precision distributed 3D shape sensing technology based on multi-core fiber, improves the space resolution of the distributed sensing by employing the optical frequency domain reflectometry, realize the multiple parameter measurement at the same position by applying special multi-core fiber structures, and finally develop a high precision 3D shape sensing technology with a track reconstruction accuracy of millimeter by establishing a reverse model from the sensing parameters to the characterizing the 3D shape.

三维姿态测量在微创手术器械的跟踪定位、飞行器疲劳损伤的形变预警、连续体机器人的运动轨迹控制等工程领域具有重要作用，其中跟踪定位精度、轨迹精确重构、实时监测能力是三维姿态测量的核心参数。光纤传感由于具有抗电磁干扰、易复用、测量快、灵敏度高等优点，非常适合于三维姿态测量，但目前光纤姿态测量技术的跟踪定位和轨迹重构精度还局限在厘米量级，远达不到微创医疗和智能结构监控等领域的要求。多芯光纤具有多维度、多参数分布式传感能力，可为轨迹矢量空间的建立提供保障。为此，结合项目组在多芯光纤器件制作和分布式光纤传感等技术方面的基础，本项目提出了基于多芯光纤瑞利背向散射的高精度、分布式三维姿态测量关键技术研究，拟通过光频域分析技术提高分布式参数测量的空间分辨率，建立从测量参数到三维姿态表征的反演模型，最终实现一种具有毫米重构精度的三维姿态测量技术。

三维姿态测量在微创手术器械的跟踪定位、飞行器疲劳损伤的形变预警、连续体机器人的运动轨迹控制等工程领域具有重要作用，其中跟踪定位精度、轨迹精确重构、实时监测能力是三维姿态测量的核心参数。本项目主要开展了高精度、分布式光纤形状关键技术研究。.1）在搭建形状传感系统的基础上，提出局域互相关方法，解决传统互相关计算存在多峰伪峰问题。该方法摒弃了使用整段频谱进行互相关的传统方法，采用基于局部频谱更为相似的原理，计算局部频谱的欧氏距离，然后根据此距离来判断波长漂移值。采用该方法进行了裸纤应变和粘贴在钢尺上的弯曲测量，其空间分辨率为1cm，应变灵敏度为1.26pm/微应变，弯曲灵敏度为216 pm/m-1。.2）提出了一种温度不敏感的光纤形状传感方法，采用微元累积积分的重构原理，实现了桥型、水滴形、S形等复杂的二维形状的测量，单位长度重构误差可以控制在3%以内。结合计算机成像技术，设计开发了一套二维形状重构客户端，实现可视化操作。.3）我们提出一种基于螺旋七芯光纤的方向可识别的高灵敏度扭曲传感器。光纤扭转时产生剪切应力，当扭转方向与固有旋向一致时，瑞利散射光谱波长向正向漂移，其灵敏度为1.04pm/(rad/m)；当扭转方向与固有旋向相反时，瑞利散射光谱波长向负向漂移，其灵敏度为0.50pm/(rad/m)。从而实现扭转方向的识别。然而，中心光纤几乎不存在剪切应力，因此无论正反如何扭转光纤，波长始终稳定不变。.4）我们提出了一种基于单模光纤在纤马赫-曾德尔干涉仪的强度调制型扭曲传感器。采用CO2激光器在单模光纤一端产生非圆对称的微扰，从而激发非圆对称的包层模式，并与第二处微扰的纤芯模发生干涉。为了识别扭转方向，在两处微扰之间设计了一个初始扭转角度。实验和理论都表明，当光纤从逆时针方向扭转到顺时针方向旋转时，光谱的波峰/波谷分别逐渐转变为了波谷/波峰。该强度调制型扭曲传感器在-50 to 50 rad/m范围内实现了灵敏度为45.3%/(rad/cm)的可以识别方向的扭曲测量。