Zengxiang Zhou

Research and implementation of the integrated cooling system for focal plate

With the rapid development of multi-objective astronomical survey telescope technology, the heat of focal plate which high-density optical fiber positioners were mounted in has become the key factor of system precision. The new integrated cooling system designed multi curved composite grooves on the surface of focal plate for forced convection was proposed. Meanwhile, the manufacturing process, sealing structure and heat dissipation performance of the system were analyzed and tested with detail in the paper. The experimental results suggested that the new integrated cooling system of focal plate has a fast response speed and good heat dissipation performance.

Research of fiber position measurement by multi CCD cameras

Parallel controlled fiber positioner as an efficiency observation system, has been used in LAMOST for four years, and will be proposed in ngCFHT and rebuilt telescope Mayall. The fiber positioner research group in USTC have designed a new generation prototype by a close-packed module robotic positioner mechanisms. The prototype includes about 150 groups fiber positioning module plugged in 1 meter diameter honeycombed focal plane. Each module has 37 12mm diameter fiber positioners. Furthermore the new system promotes the accuracy from 40 um in LAMOST to 10um in MSDESI. That’s a new challenge for measurement. Close-loop control system are to be used in new system. The CCD camera captures the photo of fiber tip position covered the focal plane, calculates the precise position information and feeds back to control system. After the positioner rotated several loops, the accuracy of all positioners will be confined to less than 10um. We report our component development and performance measurement program of new measuring system by using multi CCD cameras. With the stereo vision and image processing method, we precisely measure the 3-demension position of fiber tip carried by fiber positioner. Finally we present baseline parameters for the fiber positioner measurement as a reference of next generation survey telescope design.

A high-density integrated optical focal plane positioning system

Modern multi-spectral sky survey requires the use of greater quantity and smaller size of the fiber positioner. This paper presents a high-density integrated optical focal plane positioning system, which includes 150 groups fiber positioning module and a 1 meter diameter honeycomb-shaped focal plane framework in that have about 150 hexagonal hole. Each module has a pedestal includes 37 holes and 37 fiber positioner of 11.8 mm diameter. 37 fiber positioner integrated can greatly reduce the difficulty of the design and installation. The modular structure also facilitates maintenance and replacement in the field of telescope, and greatly reduce the difficulty of the drive system design. Numerical simulation results show that: the honeycomb-shaped focal plane framework whose thickness is 100mm and who is in a variety of working positions and load conditions, its maximum deformation is about 0.02mm. This meet the needs of the general astronomical telescopes. The positioning accuracy of test 12mm diameter fiber positioner is about 0.04 mm, and it is expected to reach 0.01mm if have the closed-loop control.

A new measurement method of profile tolerance for the LAMOST focal plane

There were a few methods taken in the profile tolerance measurement of the LAMOST Focal Plane Plate. One of the methods was to use CMM (Coordinate Measurement Machine) to measure the points on the small Focal Plane Plate and calculate the points whether or not in the tolerance zone. In this process there are some small shortcomings. The measuring point positions on the Focal Plane Plate are not the actual installation location of the optical fiber positioning system. In order to eliminate these principle errors, a measuring mandrel is inserted into the unit-holes, and the precision for the mandrel with the hole is controlled in the high level. Then measure the center of the precise target ball which is placed on the measuring mandrel by CMM. At last, fit a sphere surface with the measuring center points of the target ball and analyze the profile tolerance of the Focal Plane Plate. This process will be more in line with the actual installation location of the optical fiber positioning system. When use this method to judge the profile tolerance can provide the reference date for maintaining the ultra error unit-holes on the Focal Plane Plate. But when insert the measuring mandrel into the unit hole, there are manufacturing errors in the measuring mandrel, target ball and assembly errors. All these errors will bring the influence in the measurement. In the paper, an impact evaluation assesses the intermediate process with all these errors through experiments. And the experiment results show that there are little influence when use the target ball and the measuring mandrel in the measurement of the profile tolerance. Instead, there are more advantages than many past use of measuring methods.

The testing scheme for the LAMOST focal plane plate

At present, the LAMOST project is in a crucial period. The machining progressing of LAMOST Focal Plane Plate has completed. The inspection of the machining quality for the Focal Plane Plate in the machining process is a pivotal work. In all of the design requirements, the most crucial standards of accuracy are the profile tolerance and the unit-holes dimensional angle. Theirs precision will influence the observation efficiency of the LAMOST. But there are more than 4000 unit-holes on the 1.75m diameter Focal Plane Plate, it is impossible to measure all unit-holes and the whole area of the Focal Plane Plate. How to measure the minimal unit-hole and get the most accurate results about the machining process, judge whether the final machining Focal Plane Plate satisfy the design requirements. The measurement scheme optimization is discussed in the paper. There are two different ways to measure the Focal Plane Plate, one is the traditional way whish use specially designed implements for the every individual parameter, the other way used the CMM to measure the pivotal design requirements such as unit-hole dimensional angle and the profile tolerance of the Focal Plane Plate. The advantage of this is saving the time and cost on the CMM, improving the efficiency for the whole measurement work, and acquires the direct vision results before measuring the Focal Plane Plate on CMM. Whereas the implement which used in the measurement need to design and machine precisely for the credible measurement results. And all the measuring work is calibrated by the CMM sampling detection. The sampling detection based on the processing technology and some implements are mentioned in the paper.

The fiber view metrology system design for spectral survey telescope

Since the large scale use of paralleled controllable fiber positioner in LAMOST, the newly designed spectral survey telescope project generally uses the fiber position unit which similar to LAMOST to obtain the target spectrum. The positioning accuracy of the fiber positioner is directly related to the performance of the telescope. In order to further improve the positioning accuracy of positioners system, it is an important way to improve the accuracy by measuring the position of the optical fiber end on the positioners by using the visual metrology system. This paper mainly introduces the research design of LAMOST closed-loop metrology system, and the closed-loop system was established in different positions within the telescope to acquire best results. The metrology system will improve the fiber positioner system operation accuracy and reliability after the completion of the entire system in the future.

The improvement of LAMOST fiber view camera metrology system fiber position recognition algorithm

The LAMOST telescope has been officially observed for the past seven years since 2009, and many parts of the telescope are currently being upgraded. The fiber positioning unit of the focal plane instrument is also planned to be upgraded again. In order to ensure a higher positioning accuracy of the fiber positioning unit, the newly developed fiber positioning system adopts a closed-loop camera to photograph the unit fiber position in real time, and feeds back to the control system to implement multiple positioning to improve the positioning accuracy. This article focuses on an improved optical center of gravity algorithm for optical fiber location based on the optical center of gravity algorithm. The factors affecting the position measurement of the optical fiber spot are optimized, and the recognition accuracy of the spot position under different conditions is improved.

Stability study of the multi-object photogrammetric platform for optical fiber units

Metrology Camera System (MCS) was designed to make a closed-loop control of the optical fiber position in Fiber Positioning System (FPS) on the focal plate of the LAMOST. The stability of the metrology platform is the key factor to the quality of camera shooting. A precise adjustable mechanism was designed in this paper to achieve the platform’s pitching and horizontal rotation adjustment. And also a vibration isolation system using Magnetic Negative Stiffness (MNS) and positive spring in parallel was designed to decrease the effect of vibration, which was caused by the multiple complex vibration loads existing in the working environment, on the platform. Furthermore, an air conditioning system using the semiconductor refrigerator and resistance heater was designed to ensure working temperature of the camera and lens in extreme temperature environments. The simulation results showed that these designs were effective to improve the stability of the metrology system

Comparison of pose error compensation for focal plane pose test platform using GRNN and CART

The surface accuracy of the telescope focal plate plays a key role in high-precision astronomical observations. The 6- DOF parallel Focal Plane Pose Test Platform (FPPTP) is used to measure the deformation and surface accuracy of the focal plate in different space pose, and precise pose adjustment is an important indicator of the platforms performance. But the factors affecting the pose error of the platform are complex and difficult to describe accurately with mathematical model. Comparison of pose error compensation for the focal plate in different space pose using Generalized Regression Neural Network (GRNN) and Classification Regression Tree (CART) is studied in this paper.

Research on active heat dissipation experimental system for focal plate

The integrated cooling system with multi curved composite grooves on the surface of focal plate was designed to solve the problem that high-density heat resource is distributed on the focal plate. The new active heat dissipation experimental system was proposed considering the wide ambient temperature variation around the focal plate. The temperature field and deformation of the focal plate in the integrated cooling system under the environment of large temperature difference were analyzed by the simulation, and the active heat dissipation system for the focal plate was achieved by precise temperature control of the cooling medium. Meanwhile, the influence of active heat dissipation system on telescope observation was analyzed by the simulation. The simulation and experimental results suggested the integrated cooling system of focal plate can ensure the temperature of the focal plate constant and the deformation error of the focal plate is within the permitted range under the large temperature difference. And the new active heat dissipation system of focal plate can have a fast response speed and good adjustment ability in the condition of the varied ambient temperature, meanwhile, can effectively reduce the effect on the telescope observation.