Large-sized potassium dihydrogen phosphate (KDP) crystals are an irreplaceable nonlinear optical component in an inertial confinement fusion project. Restricted by the size, previous studies have been aimed mainly at the removal principle and surface roughness of small-sized KDP crystals, with less research on flatness. Due to its low surface damage and high machining efficiency, water dissolution ultraprecision continuous polishing (WDUCP) has become a good technique for processing large-sized KDP crystals. In this technique, the trajectory uniformity of water droplets can directly affect the surface quality, such as flatness and roughness. Specifically, uneven trajectory distribution of water droplets on the surface of KDP crystals derived from the mode of motion obviously affects the surface quality. In this study, the material removal mechanism of WDUCP was introduced. A simulation of the trajectory of water droplets on KDP crystals under different eccentricity modes of motion was then performed. Meanwhile, the coefficient of variation (CV) was utilized to evaluate the trajectory uniformity. Furthermore, to verify the reliability of the simulation, some experimental tests were also conducted by employing a large continuous polisher. The results showed that the CV varied from 0.67 to 2.02 under the certain eccentricity mode of motion and varied from 0.48 to 0.65 under the uncertain eccentricity mode of motion. The CV of uncertain eccentricity is always smaller than that of certain eccentricity. Hence, the uniformity of trajectory was better under uncertain eccentricity. Under the mode of motion of uncertain eccentricity, the initial surface texture of the 100 mm × 100 mm × 10 mm KDP crystal did achieve uniform planarization. The surface root mean square roughness was reduced to 2.182 nm, and the flatness was reduced to 22.013 μm. Therefore, the feasibility and validity of WDUCP for large-sized KDP crystal were verified.

环形抛光是大口径平面光学材料加工的首选方式,特别是在大口径平面光学元件的超精密加工中占有重要地位。抛光盘表面形状是影响元件面形精度的直接因素。为了研究小工具对抛光盘表面材料的去除特性,首先需要准确测得抛光盘的表面形状。采用激光位移传感器采集抛光盘表面螺旋样点的高度,针对实验检测误差进行分析并标定,最终计算得到抛光盘表面的实际形状。借鉴数控小工具抛光方法,建立小工具修正下抛光盘的材料去除模型,通过仿真计算得到了在小工具修正范围内抛光盘的材料去除函数,分析了抛光盘的材料去除特性。最后通过小工具修正实验验证了仿真结果的正确性,为抛光盘的形状修正提供理论依据。

研究了高重心小抛光面的方形工件(抛光面大小30 mm×30 mm, 高90 mm)环形抛光中, 倾覆力矩对工件面形的影响。通过分析方形工件在工件孔中的运动轨迹及受力情况, 发现了工件与工件孔壁碰撞会导致工件倾斜, 高重心的工件在碰撞时倾斜幅度较大, 倾斜角度和工件与工件孔壁间的间隙有关。重心较高的方形工件, 以及工件与工件孔壁间隙的增大都会增加由倾覆力矩导致的面形变凸与畸变。在高重心小抛光面的方形工件侧面粘接玻璃靠体后, 工件的重心降低, 工件孔与工件间的间隙减小, 成功解决了面形变凸与畸变的问题, 面形PV达到0.056λ, PV-|POWER|达到0.054λ, 满足了生产需求。

针对环形抛光中抛光盘的面形难以精确控制的问题, 以Preston方程和Winkler假定为基础, 建立光学元件抛光的基本模型, 通过理论分析和计算机模拟与实验, 深入研究环形抛光的系统特性。结果表明, 系统存在一个保持盘面面形不变的状态, 此时的状态为系统的平衡状态, 在平衡状态下抛光工件时无需调整校正板位置即可连续获得高精度平面; 在不同的工况下, 系统平衡状态对应的校正板位置不相同, 应用建立的模型定量研究平衡状态下校正板位置与工件尺寸的关系。实验证明在平衡状态下抛光工件时工件的面形精度和加工效率都得到了提高。

针对大口径平面光学元件全频谱面形技术指标的高效率、高精度收敛, 研究了环形抛光技术。考虑环抛机沥青蜡盘的平面度直接影响工件面形的收敛效率, 本文利用准直激光束作为参考, 设计研制了测量精度高, 重复性精度达到±1 μm的大型环抛机抛光蜡盘平面度测量专用装置。分析了环抛过程中蜡盘表面平面度和工件面型PV值之间的变化规律和相关性, 根据测量数据得出了蜡盘平面度数据和工件面形的对应关系。实验显示: 当平面度和面形曲线相差较大时, 工件面形可快速收敛至1λ左右, 并由粗抛向精抛工序快速过渡。提出的大型环抛机抛光蜡盘平面度监测装置实现了对湿滑胶体平面的高精度、快速测量, 为环抛的确定性抛光工艺提供了重要的技术支持。

针对传统方法抛光高功率激光实验中使用的长焦距列阵透镜单元遇到的检测困难、一致性差等问题，提出了采用环形抛光的新方法。对环形抛光系统的理论分析表明，抛光盘面形可以稳定在球面状态。利用这种特性，环形抛光法可以抛光小曲率球面。阐述了抛光盘面形的调节方法。利用0.69 m 环形抛光机对口径45 mm、曲率半径57207 mm 的列阵透镜单元进行了抛光，结果表明面形精度和一致性均优于平面摆动式抛光法。最后对环形抛光机可抛光的球面曲率半径范围进行了探讨，发现盘面尺寸越小球面抛光能力越强，直径0.8 m 的盘面可抛光的曲率半径可低至10 m。

针对传统方法抛光高功率激光实验中使用的长焦距列阵透镜单元遇到的检测困难、一致性差等问题，提出了采用环形抛光的新方法。对环形抛光系统的理论分析表明，抛光盘面形可以稳定在球面状态。利用这种特性，环形抛光法可以抛光小曲率球面。阐述了抛光盘面形的调节方法。利用0.69 m 环形抛光机对口径45 mm、曲率半径57207 mm 的列阵透镜单元进行了抛光，结果表明面形精度和一致性均优于平面摆动式抛光法。最后对环形抛光机可抛光的球面曲率半径范围进行了探讨，发现盘面尺寸越小球面抛光能力越强，直径0.8 m 的盘面可抛光的曲率半径可低至10 m。

对环形抛光法加工大小口径工件面形不一致的问题进行了研究。在0.69 m 环形抛光机上发现，φ100 mm 工件面形微凹时，φ48 mm 工件为峰谷(PV)值0.336 λ(λ = 632.8 nm) 的凸面形。利用Winkler假定和Preston方程对工件的面形进行了研究，发现倾覆力矩是引起面形不一致的主要原因。对于圆形工件的理论计算结果表明，当工件和抛光盘之间的摩擦系数与分离器对工件的作用力合力的高度的乘积大于工件直径0.125 倍时，工件将会变凸。对工件进行了加压、润滑和降低工件支撑位置等实验，发现加压不能改善工件面形一致性；在抛光液中添加润滑剂后一致性有了一定的改善，φ48 mm 工件PV 值降为0.128 λ ；而降低工件支持位置后，大小口径工件面形不一致性问题得到了解决，φ48 mm 工件PV 值降为0.058 λ ，且变为微凹面。此结果表明抛光盘与工件的摩擦系数不能太大，且分离器对工件的支持位置应尽量靠进盘面。

The problem that the workpieces with different sizes have different surface figures is studied in the continuous polishing process. The surface shape is a little concave and the peak valley (PV) value is 0.336 λ (λ = 632.8 nm) for the φ100 mm workpiece when polished in the 0.69 m continuous polishing machine. However, the φ48 mm workpiece is convex and the PV value is 0.336 λ . The Winkler′s hypothesis and the Preston equation are applied to study the surface shape of the workpiece, then the overturning moment of the workpiece is found to be the main reason for the surface inconformity. The theoretical analysis results show that to the round workpiece, when the product of the friction coefficient between the workpiece and the polishing pad and the resultant force from the separator to the workpiece is larger than 0.125 times diameter of the workpiece, the workpiece will turn to convex. The experiments of workpiece pressing, lubrication and moving down the supporting position of the separator is done. The results show that the consistency isn′t been improved by applying pressure on the workpiece; by adding lubricant to the polishing slurry, the consistency is improved as the surface PV of the φ48 mm workpiece is reduced to 0.128 λ ; and the inconsistency problem is solved as the surface PV of the φ48 mm workpiece is reduced to 0.058 λ and the shape is slightly concave when moving down the supporting position. The results indicate that the friction coefficient between the polishing pad and the workpiece shouldn′t be to large and the supporting position of the separator to the workpiece should as near to the polishing surface as possible in the continuous polishing process.