高精度、自动微调CCD拼接焦面关键技术研究

The focal plane of very large mosaic CCD is the key instrument for large aperture and wide field telescope in astronomical field. It is necessary to maintain precise control of the focal plane surface over the entire field of view. At present, the focal plane assembly encountered challenges from high precision mechanical process and testing equipment. Assembling the flat focal plane is very tedious work and low efficiency. Especially when the focal plane is cooled and attached to the telescope, there are various factors that may cause the change of the surface .It is very difficult to assemble again. In order to meet the needs the large focal plane application, a new method of assembling the large scale FPA was presented. The high precision piezoelectric actuators was used to complete the position adjustment of CCD in micrometer. By imaging a regular grid of dots on the focal plane, the CCD offset along the optical axis 、tilt and pitch is converted to the variation of FWHM at different positions of mosaic CCD. The focal plane can match the telescope in the local. In this proposal, the 3×3CCD focal plane and the imaging experiment platform will be developed. With testing performances of focal plane, the feasibility and the approach of the closed-loop control method are also been discussed.

大尺寸CCD拼接焦面是天文大口径、大视场望远镜的重要部件，面型调整和精度是拼接焦面研究的关键问题。目前普遍采用的固定机械拼接技术存在机械加工难度大、拼接效率低、对高精度检测设备要求高的问题。尤其是调整好的焦面在低温真空环境和望远镜上时，存在各种可能导致面形改变的因素，再次调整十分困难。为了解决这一问题，本项目提出基于压电陶瓷电机三点支撑的高精度、自动微调机构用于焦面拼接，根据实际获得的图像质量，闭环控制、主动调整拼接焦面上每一个CCD俯仰、倾斜、光轴方向上的姿态，使拼接焦面不仅在整体、还可以在局部更精确匹配望远镜的光学系统。通过设计研制3×3CCD自动拼接焦面的实验样机，检测微调机构性能指标；建立光学成像实验平台，研究控制方法，评估实际使用效果。

大尺寸CCD拼接焦面是天文大口径、大视场望远镜的重要部件，面型调整和精度是拼接焦面研究的关键问题。项目组四年中对自动拼接焦面开展深入研究，取得一定成果。首先成功研制出关键部件，基于压电陶瓷电机三点支撑的微调机构，完成尺寸为180mm ×180mm由3×3 CCD模拟件组成的拼接焦面实验样机，开展常温下自动拼接方法和检测技术的研究，该样机调节精度<1um，调节范围±1毫米，CCD间距小于0.5mm，拼接焦面平面度P-V≦30um；建立光学成像实验平台，初步开发了基于拼接焦面对光学标准靶不同位置光斑成像图像FWHM变化，控制微调机构调整CCD姿态的算法和软件，验证自动拼接焦面技术在望远镜应用的可行性；此外项目组还扩充了研究和应用领域，在用于拼接焦面的低噪声、小型化CCD电子学方面取得良好进展，应用于9K 16通道CCD相机，实验室测试性能指标满足望远镜要求；利用微调机构，完成一台可自动微调CCD姿态的的单探测器相机，通过安装在望远镜上试观测，获得初步观测数据，效果良好。