Jianping Wang

Calibration method with separation patterns of a single-camera

Such as in LAMOST (Large Sky Area Multi-Object Fiber Spectroscopy Telescope), many photometric measurement systems need to reach sub-pixel accuracy with area scan CCD camera. The separation patterns are used to calibrate a single-camera with high precision. Several separation calibration patterns with small size are put on the position of object plane of the camera. Each pattern has some spot array with high precision. The position of each reference point on the image plane of the camera is calculated. The coordinates of the reference points on the calibration patterns are used to calibrate the camera. The curved-surface fitting method is applied to fit the perspective relationship between the object plane and the image plane. The integer pattern with large dimension can be replaced by the several small differential patterns in the situation of large field. The difficulty to manufacture the large pattern is avoided. The experimental results show that the mean value of residual error is less than 0.002mm with the separation calibration method.

Research on calibration method of LAMOST fiber robot

Large sky area multi-object fiber spectroscopy telescope (LAMOST) is an innovative reflecting Schmidt telescope. One of its key technology is 4000 dual rotational fiber robot located in the focal plane. This article analyzes the calibration requirements of the 4000 fiber robot. And then, proposes a fast calibration method in the complex field environment, and discribes the specific process how to obtain positioning parameters of the fiber robot rapidly.

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.

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

A micro-optical fiber positioner

This paper gives a scheme of optical fiber positioner structure of a miniature, by use of the DC servo motor with the diameter of 3mm driver, the distance can designed to 8.5mm, and can arrange more than 12000 fibers in the focal plane with the diameter of 1 meters, it is especially suitable for telescope with small dimension focal plane and has high density fiber positioning requirements. Based on the principle of double rotary fiber positioning principle, It consists of a hollow shaft revolving mechanism, and eccentric axis revolving mechanism relative to hollow shaft. The hollow shaft turns round at the range of -180 degrees to +180 degrees and the eccentric axis turns round at the range of -90 degrees to +90 degrees at the half of radius driving by each control motor. When positioning, the optical fiber end moves on the focal plate throughout, and can never deviate from focal plane. optical fiber is fixed in the mounting hole of fiber support which installed on the eccentric rotary shaft (fiber support’s hole axis is parallel to the axis of the hollow shaft), and fiber will lead to pass through the inner hole of the hollow shaft and focal plate then connected to the spectrometer. positioner center shaft adopts planetary gear driving principle, with small module motor’s gear and the fixed ring gear can driving motor and positioner planetary rotate, the eccentric shaft by DC servo motor with the diameter of 3mm drived coaxial optical fiber on the eccentric shaft, the center and the eccentric shafts adopts micro rolling bearing support; in order to prevent the positioner’s center and eccentric shaft to rotate out of bounds, both limiting devices have designed to ensure the safety of fiber positioning; both center and eccentric shaft are designed with a spring structure to eliminate the influence of gear clearance; because positioner size is very small, the positioner driving wire is embedded in the slot of the hollow shaft sleeve wall. This will not affect the fiber go through the center shaft’s holes and pass through the focal plane; positioner sample test results show that the closed-loop positioning can reached accuracy of 0.01mm unit, and can meet with the demand of optical fiber positioning.