Fiber Positioning System of LAMOST focal plane based on subarea thinking, adopts a parallel controllable
positioning plan, the structure is designed as a round area and overlapped each other in order to eliminate the
un-observation region. But it also makes the observation efficiency of the system become an important problem. In this
paper According to the system, the model of LAMOST focal plane Observation Planning including 4000 fiber
positioning units is built, Stars are allocated using netflow algorithm and mechanical collisions are diminished through
the retreat algorithm, then the simulation of the system's observation efficiency is carried out. The problem of
observation efficiency of LAMOST focal plane is analysed systemic and all-sided from the aspect of overlapped region,
fiber positioning units, observation radius, collisions and so on. The observation efficiency of the system in theory is
describes and the simulation indicates that the system's observation efficiency is acceptable. The analyses play an
indicative role on the design of the LAMOST focal plane structure.
This paper proposes research of a structure of LAMOST fiber positioning medium-term system; its construction and its tests are briefly introduced. This medium-term system includes several parts as follow: a main control computer, a unit controller, a set of drive circuits, 19 optical positioning units that positioning 19 optical fiber ends on the small simulate focal plane with diameter of 180 mm, a CCD camera, a frame grabber, and control programs. Tests on the system have indicated that positioning precision of 19 units is less than 0.04 mm on the whole focal plane with diameter of 180 mm. On medium-term system, some important problem for LAMOST building has test and research, for example: Fiber positioning precision, mechanism interference among the units, anti-jamming of drive circuits, unit's work life-span and reliability, temperature raising, etc. Test results have established stability foundation for LAMOST construction.
The architecture of the software which controls the LAMOST fiber positioning sub-system is described. The software is composed of two parts as follows: a main control program in a computer and a unit controller program in a MCS51 single chip microcomputer ROM. And the function of the software includes: Client/Server model establishment, observation planning, collision handling, data transmission, pulse generation, CCD control, image capture and processing, and data analysis etc. Particular attention is paid to the ways in which different parts of the software can communicate. Also software techniques for multi threads, SOCKET programming, Microsoft Windows message response, and serial communications are discussed.
The observation region of fiber positioning unit of LAMSOT is designed as a round area and overlapped each other in order to eliminate the un-observation region and increase the efficiency of the observation. But in such structure, the fiber holders have probability to touch each other during moving to the target images. This paper introduces a method of an observation planning for LAMOST sub-system including 19 fiber positioning units which can diminish the probability of mechanical interference by proper assignment ways and the preparatory processing in which the interference would be detected and eliminated through the retreat algorithm, and the strategy of allocating images and the moving routes of all units are obtained. The computer simulation indicates that this method successfully avoids the mechanical collisions during observations of Sub-system, at the same time, the efficiency of the observation is hardly decreased. This method is definitely valuable to the parallel controllable optical fiber position system of LAMOST which has 4000 fiber positioning units.
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