现有方法常将相机从下至上拍摄标记物图像，当桨叶扭转幅度较大时，相机主光轴与标记物平面法向量存在明显夹角，导致拍摄图像存在透视畸变现象，从而引发较大测量误差。为解决上述问题，提出一种基于透视变换的直升机桨根扭转角测量方法。首先，将靶标垂直固定在桨叶下方，相机正对桨毂拍摄图像。其次，计算桨叶在低速拉平状态下待测方位与正方位靶标图像中的四个顶点坐标，并求解待测方位的透视变换矩阵，然后利用透视变换矩阵对桨叶高速运动状态下待测方位拍摄的畸变图像进行校正。最后，求得基准图像与校正后图像中的圆心坐标，进而计算出待测方位扭转角。实验结果表明，各方位测量误差均小于0.2°。该方法不但测量精度高，而且具有多方位动态测量的优点，在直升机旋翼桨叶运动参数测量领域具有良好的应用前景。

基于光内送粉激光熔化沉积（laser melting deposition, LMD）技术，研究变截面薄壁空心弯扭结构件的成形工艺。针对该类复杂结构件成形轨迹规划的难点，提出空间轨迹单元离散分层法对结构件进行分层并生成离散沉积单元，按设计的路径进行每个离散沉积单元的沉积。针对在实际成形过程中由于机械臂采用线段单元拟合的方式实现光滑曲线运动导致的误差，提出空间变姿态基点偏移补偿技术，对成形过程中实际姿态变化基点的位置偏移进行补偿，以此实现对尺寸误差的有效控制。最终实现变截面薄壁空心弯扭结构件的激光熔化沉积成形，成形所得结构件尺寸精度较高，形状尺寸误差在−0.44%~1.83%之间，结构件平均厚度在5.9~6.19 mm之间，结构件显微硬度在269~282.2 HV之间，结构件表面和内部皆致密均匀，无明显的气孔、裂缝等缺陷。

We propose a high-sensitivity bidirectional torsion sensor using a helical seven-core fiber taper embedded in multimode fiber (MHSTM). Sensors with different taper waists and helical pitches are fabricated, and their transmission spectra are obtained and analyzed. The waist and length of the sandwiched seven-core fiber are finally determined to be 68 µm and 3 mm, respectively. The experimental results show that the clockwise and counterclockwise torsion sensitivities of the proposed sensor are 2.253 nm/(rad/m) and -1.123 nm/(rad/m), respectively. When tapered waist diameter reduces to 48 µm, a superior torsion sensitivity of 5.391 nm/(rad/m) in the range of 0–4.24 nm/(rad/m) is obtained, which is 46 times as large as the traditional helical seven-core fiber structure. In addition, the MHSTM structure is also relatively stable to temperature variations.

We propose and investigate a compact optical fiber sensor that aims to measure the torsion in both amount and direction with high sensitivity. This sensor is configured by a triangular-prism-shaped long-period fiber grating, which is fabricated by the high frequency CO2 laser polished method. The unique design of the triangular-shaped structure breaks the rotational symmetry of the optical fiber and provides high sensitivity for torsion measurement. In preliminary experiments, the torsion response of the sensor achieves a good stability and linearity. The torsion sensitivity is 0.54 nm/(rad/m), which renders the proposed structure a highly sensitive torsion sensor.

A novel phase-shifted long-period fiber grating (PS-LPFG) for the simultaneous measurement of torsion and temperature is described and experimentally demonstrated. The PS-LPFG is fabricated by inserting a pre-twisted structure into the long-period fiber grating (LPFG) written in single-mode fiber (SMF). Experimental results show that the torsion sensitivities of the two dips are ?0.114 nm/(rad/m) and ?0.069 nm/(rad/m) in the clockwise direction, and ?0.087 nm/(rad/m) and ?0.048 nm/(rad/m) in the counterclockwise direction, respectively. The temperature sensitivities of the two dips are 0.057 nm/°C and 0.051 nm/°C, respectively. The two dips of the PS-LPFG exhibit different responses to torsion and temperature. Simultaneous measurement of torsion and temperature can be implemented using a sensor. The feasibility and stabilization of simultaneous torsion and temperature measurement have been confirmed, and hence this novel PS-LPFG demonstrates potential for fiber sensing and engineering applications.