KEYWORDS: Actuators, Active optics, Polishing, Telescopes, Surface finishing, Adaptive optics, Control systems, Mirrors, Deformable mirrors, Control systems design
Optical plates (OP) play more and more important role in modern ground-based telescopes. They can be as segments
composing primary mirror, deformable mirror for correcting air turbulence or active stressed lap used in polishing large
aspherical optics. When control the deformation of these plates, we always confronts with common situations: high
shape precision requirement, rapid deformation frequency with real time demand, intrinsic multi-channel coupling
characteristic. So how to improve OP deformation performance becomes a critical task in practical design. In this paper,
the control principle of OP is first introduced. Then a three-layer control architecture is presented. They are application
layer, real time control layer and motion execution layer. After that we designed a prototype system following this
framework, targeting active stressed polishing lap which has twelve motion channels. Both the hardware and software
development are discussed thereafter. OP surface deformation experiments are carried out and surface shape obtained
using LVDT array. Results verify the effectiveness of the design. And we are looking forward to use this control design
in more channel and time demanding applications.
KEYWORDS: Control systems, Control systems design, Mirrors, Astronomical imaging, Data acquisition, Astronomy, Aspheric lenses, Sensors, Astronomical telescopes, Telescopes
We have designed an active stressed lap and its control mode is that an computer sends control orders to the control
system of the active stress lap, under windows operating system. The control mode has a shortage, which is a limit exists
when we use the lap to complete an aspheric surface deformation task with a fast focal ratio, because windows system is
not real-time. Therefore, we have designed a real-time deformation control system for the active stressed lap.
The paper makes an introduction to the structure of the deformation control system of the active stressed lap.
Secondly, gives a detailed presentation on the design of the test system from software and hardware two
aspects .Finally, the paper makes a dynamic response test on the deformation control system of stressed lap, a stability
test on the control system and an overall performance test.
The active stressed lap polishing technology is a kind of new polishing technology that can actively deform the lap
surface to become an off-axis asphere according to different lap position on mirror surface and different angle of lap. The
pressure of the lap on the mirror is an important factor affecting the grinding efficiency of the optics mirror. The active
stressed lap technology using dynamic pressure control solution in the process of polishing astronomical Aspheric Mirror
with faster asphericity will provide the advantage like high polishing speed and natural smooth, etc. This article puts
emphases on the pressure control technology of the active stressed lap technology. It requires that the active stressed lap
keeps symmetrical vertical compression on the mirrors in the process of grinding mirrors. With a background of an
active stressed lap 450mm in diameter, this article gives an outline of the pressure control organization, analyzes the
principle of pressure control and proposes the limitations of the present pressure control organization and the relevant
solutions, designs a digital pressure controller with C32-bit RISC embedded and gives the relevant experimental test result finally.
KEYWORDS: Telescopes, Space telescopes, Computer programming, Astronomical telescopes, Control systems, Control systems design, Astronomy, Servomechanisms, Composites, Optical instrument design
Along with the development of space and astronomy science, production of large aperture telescope and super
large aperture telescope will definitely become the trend. It's one of methods to solve precise drive of large aperture
telescope using direct drive technology unified designed of electricity and magnetism structure. A direct drive precise
rotary table with diameter of 2.5 meters researched and produced by us is a typical mechanical & electrical integration
design. This paper mainly introduces position measurement control system of direct drive motor. In design of this motor,
position measurement control system requires having high resolution, and precisely aligning the position of rotor shaft
and making measurement, meanwhile transferring position information to position reversing information corresponding
to needed motor pole number. This system has chosen high precision metal band coder and absolute type coder,
processing information of coders, and has sent 32-bit RISC CPU making software processing, and gained high
resolution composite coder. The paper gives relevant laboratory test results at the end, indicating the position
measurement can apply to large aperture telescope control system. This project is subsidized by Chinese National
Natural Science Funds (10833004).
KEYWORDS: Polishing, Mirrors, Optical fabrication, Control systems, Surface finishing, Astronomy, Optics manufacturing, Motion controllers, Control systems design, Feedback control
Mirrors with large aperture, high asphericity and tight shape tolerances are indispensable for modern astronomical
telescope. This pressing demand provides new challenges on optical fabrication. Paper here presents a 2.5m CNC
machine which has been designed and constructed in Nanjing Institute of Astronomical Optics & Technology (NIAOT).
Mechanical layout of 2.5m OFM is first studied basing on analyzing fabrication requirements. Equipped with six motion
axes, it can process parts up to 2500mm in diameter. Rotary symmetrical component can be finished under cylindrical
coordinates and Cartesian coordinates are applied for off-axis workpiece. Then control system using CAN field bus is
discussed. This control architecture offers many characteristics, such as high openness, expansibility and flexibility.
Since 2.5m OFM is developed to combine faculties of grinding, lapping and polishing, we arrange a series of tests for
each function. Now a 1.1m hexagonal mirror is carried for grinding. Polishing test using sub-aperture tool and active
stressed lap will be programmed later.
KEYWORDS: Control systems, Polishing, Control systems design, Actuators, Mirrors, Microcontrollers, Sensors, Signal processing, Surface finishing, Astronomy
A 450mm diameter active stressed lap has been developed in NIAOT by 2003. We design a new lap in 2007. This
paper puts on emphases on introducing the new deforming control system of the lap. Aiming at the control
characteristic of the lap, a new kind of digital deforming controller is designed. The controller consists of 3 parts:
computer signal disposing, motor driving and force sensor signal disposing. Intelligent numeral PID method is applied
in the controller instead of traditional PID. In the end, the result of new deformation are given.
NIAOT has made a stressed lap polishing machine and finished a φ910mm, F/2.0 paraboloid. In the process we found shape control strategy is an important technology for stressed lap polishing tool and this kind of content has not been discussed systematically before. So this paper mainly dedicates to the method of lap shape control. Firstly a mathematical model of stressed lap is introduced. Then three shape control methods are put forward one by one concerning aspects as shape accuracy and deformation hysteresis. The fundamental method is least square algorithm. On the base of it we put forward its reformation form: least square algorithm with damping factor. To get more satisfied performance a new algorithm using optimization under constrains of linear inequalities is proposed. Through theoretical analysis and computer simulation some comparisons are made among three methods. Finally we have done experiments using stressed lap polishing machine in NIAOT and the results obtained substantiate the feasibility and efficiency of our method.
A special computer controlled polishing machine and a 450mm diameter active stressed lap have been developed
in NIAOT, and the lap has been successfully applied on polishing a f/2, Φ910mm paraboloidal mirror. This paper briefly
introduces the control structure of the polishing system. The deformation technology is an important part of the stressed
lap. This paper puts emphases upon discussing the deformation technology. On the base of experiments on f/2 mirror,
deformation experiments on f/1.5, f/1.2 have been done also. As the asphericity becomes faster, the dynamic response
of the lap's deformation becomes slower and the error of shape becomes bigger. In order to solve this problem and
improve deformation precision, we analyse the reason for the error of the lap and discuss the dedormation emendating
problem. In the end according to the result of deforming experiments, several considerations for optimization of
mechanic-electric design of the stressed lap are given.
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