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依据上述检测方法,设计了离焦检测系统,并在实验室的气浮平台上搭建了一套装置对此离焦检测系统进行检测,如图4所示。
笔者研究所设计的离焦检测系统的物镜焦距为1 500 mm,裂像镜倾角为12°。取一焦距为100 mm的光学系统和一探测器模拟被测激光测距机接收系统。物镜焦距和被测系统焦距由焦距仪测量,焦距仪的测量误差一般为0.5%,裂像镜倾角加工误差为
$\partial {{\alpha}} {\rm{ = }}10''$ 。进行系统检测时,把被测探测器放置在此光学系统焦点附近。打开激光器,激光器发出的光束经过半反半透波片,100 mm焦距光学系统,照亮被测探测器。被测探测器反射的光沿原光路返回,经过离焦检测系统,汇聚到CCD上并被捕捉,计算机能显示出离焦信息,如图5所示。给被测探测器一个确定的位移量,同时测量并记录其离焦量的大小。表1给出三组实验测量数据(I、II、III、Ⅳ、Ⅴ、Ⅵ),ACT表示实际离焦量,MEA表示测量离焦量,1、2、3、4、5分别为5次的实际测量的离焦量值。
ACT/mm MEA MEA average/mm 1 2 3 4 5 I 1 0.986 1.005 0.985 0.995 1.012 0.997 II 2 1.971 2.022 2.024 1.973 1.992 1.996 III 3 2.957 3.024 3.002 3.041 2.987 3.006 Ⅳ 4 4.051 4.033 3.947 4.046 3.965 4.008 Ⅴ 5 5.066 4.929 5.063 5.020 4.981 5.012 Ⅵ 6 5.920 6.080 5.995 6.051 6.025 6.014 Table 1. Measurement data
从表2的三组数据分析结果可以看出,标准差、最大误差、极限误差,随着离焦量的增加而增大。离焦量为0~6 mm的时候,检测精度可以达到0.07 mm。
Standard deviation/mm Maximum error/mm Limit error/mm I 1.181×10−2 0.015 1.373×10−2 II 2.564×10−2 0.029 2.982×10−2 III 3.289×10−2 0.043 3.824×10−2 Ⅳ 4.870×10−2 0.051 5.663×10−2 Ⅴ 5.795×10−2 0.071 6.738×10−2 Ⅵ 6.132×10−2 0.080 7.131×10−2 Table 2. Experimental analysis results
根据表1和表2的数据绘制得到离焦量测量值平均值拟合曲线、理论误差曲线和极限误差曲线,如图6所示。
从图中可以看出,离焦量测量值平均值拟合曲线线性度近似为1;把理论误差曲线与极限误差曲线进行对比,可以明显看出理论误差曲线基本高于极限误差曲线,误差较为接近理想值,说明此离焦检测系统能够实现激光测距系统接收系统探测器离焦量的高精度测量。
Application of split-image mirror in defocus detection of laser rangefinder
doi: 10.3788/IRLA20200454
- Received Date: 2020-12-20
- Rev Recd Date: 2021-04-15
- Publish Date: 2021-10-20
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Key words:
- defocus detection /
- split-image mirror /
- precision analysis /
- laser rangefinder
Abstract: In order to reduce the impact of the detector out-of-focus problem on the laser rangefinder system, an active rangefinder detector adjustment system based on split-image mirror was designed. Firstly, the imaging principle of the split-image mirror was analyzed, and its the detection accuracy was theoretically analyzed, and a mathematical model of split-image defocus was established; Secondly, in view of the error factors that affected the detection, the error curve under different values was given, and the change trend of the detection accuracy was obtained; Finally, the theoretical prototype was designed and verified by experiments. The experimental results show that when the defocus is 0-6 mm, the detection accuracy can reach 0.07 mm, close to the ideal value, and the smaller the defocus, the higher the defocus detection accuracy, which is in line with the installation and measurement habits. The defocus detection system provides a new method for the adjustment of non imaging photoelectric detector, which can further improve the measurement accuracy of laser rangefinder system.