Research On Key Techniques Of Large-scale Focal Plane Splicing

For the national strategic needs of space situational awareness and environmental monitoring,space telescopes are developing towards large field of view and large aperture in view of the increasingly high demand for image quality and field of view in space astronomy and other fields.Although image sensors of large target plane have been developed continuously at home and abroad,such as 6k×6k,9k×9k and other image sensors,monolithic image sensors still cannot meet the needs of large aperture and large field of view telescopes for large focal plane,so it has become necessary to realize large focal plane by combining multiple image sensors.The splicing focal surface is the key component of the large field telescope to complete the observation task,and its surface shape is the key factor affecting the image quality,so the splicing focal surface has strict requirements on the overall flatness after the splicing.The splicing focal surface deforms under the influence of temperature,gravity,assembling technology and other factors.These deforms lead to the flatness error of the main focal surface,resulting in local defocusing of the system,resulting in image blur and image quality reduction.To summarize the key problems to be solved in this paper,the main research content is as follows.The background of large-scale focal plane splicing is studied and the significance of focal plane splicing is explained.This paper summarizes and classifies the research status and splicing methods of large-scale focal plane splicing at home and abroad,compares the advantages and disadvantages of current focal plane splicing methods,and selects the appropriate focal plane splicing methods.A large scale focal plane splicing method based on optical,mechanical and thermal integrated analysis is proposed.The concept,characteristics,general flow and application of the final analysis results are systematically studied,and the theoretical knowledge of optical,mechanical and thermal integrated analysis used in this method is summarized.The key technical difficulties in large-scale focal plane stitching and their effects on the final imaging quality of the system are systematically analyzed.Taking the focal plane splicing of a certain type of task with the scale of 4×4 as an example,16 pieces of CMOS image sensors were spliced by mechanical direct splicing method.The size of the main focal plane after splicing is about 267mm×289mm.The Bipod structure is designed as the support structure of the splicing focal plane.The flexible structure can release the assembly stress and thermal stress to a certain extent,so as to reduce the deformation of the main focal plane.The main focal plane splicing scheme and flatness non-contact detection scheme are designed,and the splicing process is described in detail.To carry out thermal design and thermal analysis of splicing focal surface,it is necessary not only to ensure the working temperature of CMOS image sensor,but also to ensure the temperature uniformity of splicing focal surface.Four low-temperature heat pipes are installed on the back of the splicing substrate in a "cross" arrangement,and the other end of the heat pipe is thermally connected to the refrigeration device.An error allocation method based on optical,mechanical and thermal integration is proposed to evaluate the deformation of splicing focal surface caused by gravity and temperature.The source of the flatness error of splicing focal surface is analyzed,and the two important error parameters,gravity and temperature,are accurately allocated according to the results of the integrated analysis of optical,mechanical and thermal.Designed and put into production a set of all-aluminum simulation of focal plane splicing,and completed the whole process verification of focal plane splicing technology and process.The deformation of splicing coke surface caused by gravity is analyzed and the error caused by gravity is also reassigned.At room temperature,the flatness of splicing focal surface was measured by non-contact measuring equipment.According to the detection results,the steel pad on the back of the CMOS image sensor with abnormal flatness was replaced to ensure the flatness of the main focal plane and the experimental measurement was carried out again.As a key component of a large field telescope,the planar surface of the spliced focal surface has a great influence on the final image quality.In this paper,the planeness of the photosensitive surface of the splicing focal surface is minimized in a controllable range through the integration of mechanical and thermal design.The key techniques of large-scale focal plane splicing studied in this paper include structure design,thermal design,flatness error distribution of main focal plane,etc.,which can be used as reference for large aperture telescope focal plane splicing.