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.
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.
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 platform's 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.
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.
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
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.
An optical transmitting antenna for visible light communication(VLC) is designed in this work, in which the antenna is positioned before the light-emitting diodes (LED) source to change the lighting distribution, in order to achieve uniform received power effect. The method to design antenna is introduced into physical optical lens principle. According to the energy conservation law and Snell law, the antenna is designed via establishing energy mapping between the luminous flux emitted by a LED source with Lambertian distribution and the target plane. The coordinates of the antenna model are obtained under matrix laboratory (MATLAB). The antenna model entity is generated through three dimensional (3D) composition software AutoCAD with the coordinates of antenna. Ray-tracing software Tracepro is used to trace the ray which through antenna, and validate the irradiance maps. The uniformity of illumination and received power of the designed VLC is improved from approximately 35% to over 83%.
In this paper, the direct current (DC)-biased optical orthogonal frequency division multiplexing (DCO-OFDM) visible light communication (VLC) system using modified μ-law companding is modeled and investigated. The simulation results reveal that the high peak to average power ratio (PAPR) induced by multi-carrier modulation (MCM) and DC bias, can aggravate signal distortion that is caused by the nonlinear characteristic of light emitting diode (LED). Thus, a pre-distortion method based on modification of μ-law companding is proposed for DCO-OFDM VLC system to resolve this problem. With the proposed method, the system can achieve a good performance of PAPR reduction and bit error rate (BER), compared to the original DCO-OFDM VLC system. It is demonstrated that the modified μ-law companding is appropriate to alleviate LED nonlinearity without degradation of the signal quality in DCO-OFDM VLC system.
Mask exchange system is the main part of Multi-Object Broadband Imaging Echellette (MOBIE) on the Thirty Meter Telescope (TMT). The robot is one of the key parts in the mask exchange process. In view of the facts that the scheme the on-board robot is hard to meet the requirements of TMT and the traditional industrial robot is difficult to use in the Mask Exchange System (MEX). The delta parallel mechanism has much advantages such as good dynamic performance, high speed and could integrate a vision recognition system to identify the masks. The design for MEX based on off-board Delta parallel mechanism was proposed in the paper.
The surface accuracy of astronomical telescope focal plate is a key indicator to precision stellar observation. Combined with the six DOF parallel focal plane attitude measurement instrument that had been already designed, space attitude error compensation of the attitude measurement instrument for the focal plane was studied in order to measure the deformation and surface shape of the focal plane in different space attitude accurately.
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.
In this paper, a compact optical fiber positioner is proposed, which is especially suitable for small scale and high density optical fiber positioning. Based on the positioning principle of double rotation, positioner’s center shaft depends on planetary gear drive principle, meshing with the fixed annular gear central motor gear driving device to rotate, and the eccentric shaft rotated driving by a coaxial eccentric motor, both center and the eccentric shaft are supported by a rolling bearings; center and eccentric shaft are both designed with electrical zero as a reference point, and both of them have position-limiting capability to ensure the safety of fiber positioning; both eccentric and center shaft are designed to eliminating clearance with spring structure, and can eliminate the influence of gear gap; both eccentric and center motor and their driving circuit can be installed in the positioner’s body, and a favorable heat sink have designed, the heat bring by positioning operation can be effectively transmit to design a focal plane unit through the aluminum component, on sleeve cooling spiral airway have designed, when positioning, the cooling air flow is inlet into install hole on the focal plate, the cooling air flow can effectively take away the positioning’s heat, to eliminate the impact of the focus seeing. By measuring position device’s sample results show that: the unit accuracy reached 0.01mm, can meet the needs of fiber positioning.
In the telescope observation, the position of fiber will highly influence the spectra efficient input in the fiber to the spectrograph. When the fibers were back illuminated on the spectra end, they would export light on the positioner end, so the CCD cameras could capture the photo of fiber tip position covered the focal plane, calculates the precise position information by light centroid method and feeds back to control system. A set of fiber back illuminated system was developed which combined to the low revolution spectro instruments in LAMOST. It could provide uniform light output to the fibers, meet the requirements for the CCD camera measurement. The paper was introduced the back illuminated system design and different test for the light resource. After optimization, the effect illuminated system could compare with the integrating sphere, meet the conditions of fiber position measurement.Using parallel controlled fiber positioner as the spectroscopic receiver is an efficiency observation system for spectra survey, has been used in LAMOST recently, and will be proposed in CFHT and rebuilt telescope Mayall. In the telescope observation, the position of fiber will highly influence the spectra efficient input in the fiber to the spectrograph. When the fibers were back illuminated on the spectra end, they would export light on the positioner end, so the CCD cameras could capture the photo of fiber tip position covered the focal plane, calculates the precise position information by light centroid method and feeds back to control system. After many years on these research, the back illuminated fiber measurement was the best method to acquire the precision position of fibers. In LAMOST, a set of fiber back illuminated system was developed which combined to the low revolution spectro instruments in LAMOST. It could provide uniform light output to the fibers, meet the requirements for the CCD camera measurement and was controlled by high-level observation system which could shut down during the telescope observation. The paper was introduced the back illuminated system design and different test for the light resource. After optimization, the effect illuminated system could compare the integrating sphere, meet the conditions of fiber position measurement.
A joint algorithm, integrating selective mapping (SLM) and restorable clipping (RC), is proposed for the direct current-biased optical orthogonal frequency division multiplexing (DCO-OFDM) and visible light communication (VLC) system to reduce the nonlinearity impacts of light-emitting diode (LED) aggravated by high peak-to-average power ratio (PAPR) and DC-bias. The performance of DCO-OFDM VLC system is analyzed and discussed with different techniques of LED nonlinearity alleviation. The simulation results show that compared to the original DCO-OFDM VLC system, the system with the proposed scheme can achieve about 4.8 dB improvement of PAPR reduction and 7 dB improvement of bit error rate (BER) performance. The reason is that the signals acquiring the desired shape in LED linear region can be recovered correctly without distortion induced by LED nonlinearity. It is demonstrated that the proposed SLM-RC technique effectively reduces not only PAPR but also the impacts of LED nonlinearity without BER deterioration.
Mask exchange system is an important part of the Multi-Object Broadband Imaging Echellette (MOBIE) on the Thirty Meter Telescope (TMT). To solve the problem of stiffness changing with the gravity vector of the mask exchange system in the MOBIE, the hybrid parallel mechanism design method was introduced into the whole research. By using the characteristics of high stiffness and precision of parallel structure, combined with large moving range of serial structure, a conceptual design of a hybrid parallel mask exchange system based on 3-RPS parallel mechanism was presented. According to the position requirements of the MOBIE, the SolidWorks structure model of the hybrid parallel mask exchange robot was established and the appropriate installation position without interfering with the related components and light path in the MOBIE of TMT was analyzed. Simulation results in SolidWorks suggested that 3-RPS parallel platform had good stiffness property in different gravity vector directions. Furthermore, through the research of the mechanism theory, the inverse kinematics solution of the 3-RPS parallel platform was calculated and the mathematical relationship between the attitude angle of moving platform and the angle of ball-hinges on the moving platform was established, in order to analyze the attitude adjustment ability of the hybrid parallel mask exchange robot. The proposed conceptual design has some guiding significance for the design of mask exchange system of the MOBIE on TMT.
Mask exchange system is the main part of Multi-Object Broadband Imaging Echellette (MOBIE) on the Thirty Meter Telescope (TMT). According to the conception of the TMT mask exchange system, the pre-design was introduced in the paper which was based on IRB 140 robot. The stiffness model of IRB 140 in SolidWorks was analyzed under different gravity vectors for further error compensation. In order to find the right location and path planning, the robot and the mask cassette model was imported into MOBIE model to perform different schemes simulation. And obtained the initial installation position and routing. Based on these initial parameters, IRB 140 robot was operated to simulate the path and estimate the mask exchange time. Meanwhile, MATLAB and ADAMS software were used to perform simulation analysis and optimize the route to acquire the kinematics parameters and compare with the experiment results. After simulation and experimental research mentioned in the paper, the theoretical reference was acquired which could high efficient improve the structure of the mask exchange system parameters optimization of the path and precision of the robot position.
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.
Multi-objects survey system because of its high efficiency have been planned to build in many telescope such as
Mayall 4m telescope and have been working well on LAMOST. The telescope could control massively robotic fiber-positioners
carried with fibers on the top, received thousand galaxies and quasi-stellar objects at one time observation.
How to measure every fiber's position accurately is the key techniques for the telescope to improve its performance.
There is a good way to measure the fiber’s position by photogrammetry with no touches measurement. The camera
could capture the position of backside illuminated fibers. In this paper we described the trial measurement for multi
positioners system in different measuring parameters, and compared these conditions which influenced the measuring
accuracy. Finally the test results were presented the baseline parameters for the measurement system to provide a site
measurement option for the positioner location.
The surface accuracy of astronomical telescope focal plate is a key indicator to precision stellar observation. To conduct
accurate deformation measurement for focal plate in different status, a 6-DOF hexapod platform was used for attitude
adjustment. For the small adjustment range of a classic 6-DOF hexapod platform, an improved structural arrangement
method was proposed in the paper to achieve ultimate adjustment of the focal plate in horizontal and vertical direction.
To validate the feasibility of this method, an angle change model which used ball hinge was set up for the movement and
base plate. Simulation results in MATLAB suggested that the ball hinge angle change of movement and base plate is
within the range of the limiting angle in the process of the platform plate adjusting to ultimate attitude. The proposed
method has some guiding significance for accurate surface measurement of focal plate.
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.
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.
The focal plate is one of the most important components of the LAMOST, whose shape precision to be centripetal and
spherical structure of multi-hole. The hole drilling distortion duing to residual stress becomes one of the striking
problems. Studying on the distortion prediction, this paper adopts the finite element simulation based on the metal
cutting principles. The distribution to the surface residual stress is achieved by building the FEM model using
ANSYS .The influence of cutting depths on the distortion of the focal plate was investigated. With the confirmation of
the final CMM test result, the deviation which compared the measuring point with the theoretical sphere is less than
0.066mm. The result showed that the FEM analysis is an effective method which predicts the machining distortion of the
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 biggest concern in the use of radio-over-fiber (ROF) links in wireless access is the limited dynamic range due to nonlinear distortion (NLD). We introduce the configuration of the ROF system, then the Volterra series, a higher-order adaptive-filter-based nonlinearity compensation scheme, is proposed to model the system and compensate the NLD. The adaptive algorithms of least mean square (LMS) and recursive least squares (RLS) for identifying Volterra kernels are both studied. The simulated results based on the measured results show that both Volterra LMS and Volterra RLS can be used to model the system, and gradually saturating amplitude nonlinearity can be adequately linearized by the latter.
A radio-over-fiber (ROF) system that combines a wireless link and an optical fiber link is studied. After introducing the configuration and analyzing the nonlinear distortion of the system, the Volterra series is proposed and used to model the system. The adaptive least mean square (LMS) and recursive least squares (RLS) algorithms for identifying the Volterra kernel are studied. A simulation is given, which uses both Volterra LMS and Volterra RLS to model a nonlinear ROF system, and indicates that the method is efficient.
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.