小口径大视场工业内窥镜光学系统设计

史天翼; 杨磊; 刘泽武; 苏晓琴; 谢洪波

doi:10.5768/JAO202344.0101003

小口径大视场工业内窥镜光学系统设计

doi: 10.5768/JAO202344.0101003

天津大学精密仪器与光电子工程学院，光电信息技术教育部重点实验室，天津 300072

基金项目: 国防预研基金

详细信息

作者简介:
史天翼（1995—），男，硕士研究生，主要从事光学设计方面的研究。E-mail：jingyisty@tju.edu.cn

通讯作者:
杨磊（1982—），男，博士，副教授，主要从事光学设计、光电检测与成像方面的研究。E-mail：yanglei@tju.edu.cn

中图分类号: TN202
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出版历程
- 收稿日期: 2022-05-19
- 修回日期: 2022-06-13
- 网络出版日期: 2022-09-16
- 刊出日期: 2023-01-17

Optical system design of small-caliber and large-field industrial endoscope

Key Laboratory of Optoelectronics Information Technology (Ministry of Education), School of Precision Instruments and Optoelectronics Engineering, Tianjin University, Tianjin 300072, China

摘要

摘要: 近年来，内窥镜广泛应用于复杂环境下小尺寸零件缺陷检测，该文设计一种用于航空发动机叶片检测的工业内窥镜光学系统。系统基本结构采用二次成像，物镜采用非对称反远距结构，将大视场光线收束进小口径腔体中，适配镜将物镜所成一次实像放大21倍，后接对角线长42 mm高速相机。系统基于Zemax设计软件进行系统优化、公差分析和像质评价，最终系统具有大视场（120°）、细孔径（3 mm）、耐高温（25 ℃~180 ℃）等特点。由于对视场、孔径和适配镜放大率有较高要求，因此合理引入非球面提高系统成像质量，入瞳直径提高至0.5 mm，系统空间截止频率在17 lp·mm⁻¹处，全视场调制传递函数值均大于0.28，最大畸变值小于21.2 %。
- 光学设计 /
- 工业内窥镜 /
- 小口径 /
- 大视场
Abstract: In recent years, the endoscope is widely used in defect detection of small-size parts in complex environment. An industrial endoscope optical system was designed for aero-engine blade detection. The basic structure of the lens adopted secondary imaging, and the objective lens adopted asymmetrical inverse distance structure, which beamed the large field of view light into the small caliber cavity. The adaptor lens was adapted to the high speed camera in which the diagonal length was 42 mm, and it could magnify the intermediate image 21 times. The system was based on Zemax design software for system optimization, tolerance analysis and image quality evaluation, and finally the system realized the optical properties of large field of view (120°), small caliber (3 mm) and high temperature resistance (25 ℃～180 ℃). Due to the higher requirements of the field of view, caliber and adaptor magnification, the aspherical surface was reasonably introduced to improve the imaging quality of the system. The entrance pupil diameter was increased to 0.5 mm, the system spatial cut-off frequency was at 17 lp·mm⁻¹, the full-field modulation transfer function value was greater than 0.28, and the maximum distortion value is less than 21.2%.
- optical design /
- industrial endoscope /
- small caliber /
- large field of view

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图 1 内窥镜结构示意图

Fig. 1 Schematic diagram of endoscope structure

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图 2 前物镜初始结构

Fig. 2 Initial structure diagram of front objective lens

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图 3 后物镜初始结构

Fig. 3 Initial structure diagram of rear objective lens

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图 4 优化后前物镜组二维图

Fig. 4 2D diagram of optimized front objective lens group

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图 5 优化后前物镜组MTF曲线

Fig. 5 MTF curves of optimized front objective lens group

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图 6 系统拼接后结构图

Fig. 6 Structure diagram of spliced system

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图 7 系统点列图

Fig. 7 Spot diagram of system

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图 8 网格畸变图

Fig. 8 Mesh distortion diagram

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图 9 MTF曲线图

Fig. 9 MTF curves

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图 10 图像模拟

Fig. 10 Image simulation

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图 11 相对照度曲线图

Fig. 11 Curves of relative illumination

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图 12 初始高温下MTF曲线

Fig. 12 MTF curves of system at initial high temperature

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图 13 3种温度下系统的MTF曲线

Fig. 13 MTF curves of system at three temperatures

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表 1 工业内窥镜设计指标

Table 1 Design indexes of industrial endoscope

参数	指标要求	备注
物方高度/mm	13.4	—
工作距离/mm	3	—
波长/nm	710	单波长无色差
分辨率/lp·mm⁻¹	>17	像方要求充分利用相机靶面
直径（带导光束）/mm	4	光学3 mm
细管长度/mm	>20	—
耐温/℃	25～180	无热化
相机接口	F口	机械配合

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表 2 非球面面型参数

Table 2 Aspheric surface parameters

表面编号	曲率半径/mm	圆锥系数	4阶项	6阶项	8阶项
3	−3.797	−2.390	−0.024	4.030E-03	9.166E-04
27	−4.034	0.060	3.005E-03	−6.329E-04	1.236E-04
29	−22.713	−2.199	3.773E-06	−1.154E-09	−4.330E-14

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表 3 材料类型及性能参数

Table 3 Material types and performance parameters

材料	具体类型	热膨胀系数/10⁻⁷/K	折射率温度系数/10⁻⁶/℃
镜片	H-ZK3	52	3.7
	H-ZLAF50E	62	3.8
	H-LAK53B	57	3.6
	H-ZK9B	62	1.9
	H-LAF3B	80	1.2
	H-K9L	76	1.6
	H-LAK4L	60	2.9
隔圈、镜筒	304不锈钢	17	—

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表 4 系统元件公差分配

Table 4 Tolerance allocation of system elements

公差类型	允许误差值
中心厚度/mm	±0.02
表面X偏心/mm	±0.02
表面Y偏心/mm	±0.02
X轴倾斜/(˚)	±0.032
Y轴倾斜/(˚)	±0.032
折射率	±0.005
阿贝数	±0.5

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表 5 蒙特卡洛公差分析结果

Table 5 Results of Monte Carlo tolerance analysis

蒙特卡洛样本百分比/%	各视场平均值	中心视场	2视场	3视场	4视场	5视场	边缘视场
90	0.183	0.277	0.202	0.185	0.158	0.150	0.128
80	0.195	0.306	0.223	0.194	0.171	0.162	0.136
50	0.221	0.347	0.260	0.233	0.183	0.173	0.150
20	0.254	0.393	0.320	0.284	0.220	0.197	0.175
10	0.275	0.434	0.332	0.308	0.255	0.225	0.193

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