Compact high performance hybrid reluctance actuated fast steering mirror system

Fast steering mirror (FSM) is one of the most important components in electro-optical tracking system and access to FSM model is the basis for controlling and fault diagnosis. This paper presented a correlation identification method based on Invert-Repeated m-sequence which can be used in the electro-optical tracking system to achieve the model of FSM under low sampling rate. Firstly, this article discussed the properties of the Invert-Repeated m-sequence and program implemented in matlab language, then analyzed the principle of correlation identification method based on Invert-Repeated m-sequence by utilizing Wiener-Hopf equation which is simple to achieve with strong anti-jamming capability and small perturbations on the system. Finally, a FSM model with the experiment data got by Dynamic Signal Analyzer was built in Matlab/Simulink and identified by the method mentioned in the paper. The experiment showed that correlation identification method which has certain actual application value, based on Invert-Repeated m-sequence can obtain more accurate recognition results even if the FSM system’s output signal contained large variance noise.

Even though the design and tuning of proportional-integral-derivative (PID) controllers appears to be conceptually simple it can be difficult in practice, especially when competing control objectives are present. This paper presents a tuning method for PID controllers applied to low stiffness mechatronic systems that allows a direct and intuitive trade-off between the robustness and the performance of the resulting system. With the required system bandwidth typically determined by the targeted application and an according parametrization, the controller tuning is reduced to the selection of the cross-over frequency Uc and the variation of a single parameter α. It is demonstrated how the α-value influences the resulting system properties, while a larger α increases robustness but also diminishes control quality. The tuning method is experimentally verified on a fast steering mirror (FSM) system by implementing controllers with α-values of 2, 3 and 4.5. It is shown that the settling time for α = 2 is 4-times smaller than for α = 4.5, when applied to the nominal plant. On the other hand the stability margins for α = 2 are also significantly smaller, diminishing robustness and increasing oscillating transients when plant uncertainties are present. An α-value of 3 yields a good trade-off between robustness and performance of the closed-loop operated system.

In the precise pointing system of satellite laser communication, the piezoelectric fast steering mirror (FSM) is used in the system. In the free state, the hysteresis between the input voltage and the output displacement of FSM is obvious, which has a serious impact on the precision positioning accuracy. Therefore, aiming at the hysteresis problem of the fast steering mirror in satellite laser communication, a phenomenal hysteresis mathematical model based on Bouc-Wen operator is established by analyzing the hysteresis mechanism of the piezoelectric fast steering mirror. An improved nonlinear particle swarm optimization (PSO) parameter identification method is proposed, which greatly improves the optimization efficiency of particle swarm optimization. On this basis, a feedforward inverse compensation linearization method is proposed. In order to verify the effectiveness of the proposed model, a fast steering mirror system experiment is established. The experimental results show that the improved PSO parameter identification method proposed in this paper can accurately identify the parameters in the model, and the proposed feedforward linearization method can improve the linearity of piezoelectric ceramic actuator by more than 90%, which can meet the actual index requirements of the fast steering mirror.KeywordsFast steering mirrorHysteresisBouc-WenFeedforward linearization

The fast steering mirror is a commonly used image motion compensation device in space cameras. The mechanical properties of the support structure will directly affect the response speed and closed loop bandwidth of the fast steering mirror system. A fast steering mirror driven by voice coil motor in a low earth orbit space camera was taken as the research object, and a two-axis flexible support structure based on cross-shaped flexible hinges was designed, which had the advantages of compact structure and small center drift. According to the approximate differential equation of cantilever beam deflection, the mathematical model of the rotational stiffness of the two-axis flexible support was established. The main structural parameters of the flexible hinge were selected for the resonant frequency requirements of the fast steering mirror mechanism, and a modal analysis of the mechanism was performed by using the finite element software MSC.Patran. The analysis results show that the resonant frequency of the fast steering mirror mechanism in the two working directions is 18.6 Hz and 18.7 Hz, while the resonant frequencies in other non-working directions are above 292.2 Hz, which proves that the choice of flexible hinge structural parameters is reasonable. In order to test the correctness of the theoretical model, a prototype of the fast steering mirror was processed and the experimental platform was built. The rotational stiffness and resonant frequency of the mechanism were tested. The results of the test and the theoretical analysis are consistent within the allowable error range.

The Fast Steering Mirror (FSM) of the GMT is going to be the first-light secondary mirror system. An FSM prototype has been developed which consists of 1 m off-axis aspheric mirror and tip-tilt test-beds. The successful development results are presented.

The Giant Magellan Telescope (GMT) is one of Extremely large telescopes, which is 25m in diameter featured with two Gregorian secondary mirrors, an adaptive secondary mirror (ASM) and a fast-steering secondary mirror (FSM). The FSM is 3.2 m in diameter and built as seven 1.1 m diameter circular segments conjugated 1:1 to the seven 8.4m segments of the primary. The guiding philosophy in the design of the FSM segment mirror is to minimize development and fabrication risks ensuring a set of secondary mirrors are available on schedule for telescope commissioning and early operations in a seeing limited mode. Each FSM segment contains a tip-tilt capability for fine co-alignment of the telescope subapertures and fast guiding to attenuate telescope wind shake and mount control jitter, thus optimizing the seeing limited performance of the telescope. The final design of the FSM mirror and support system configuration was optimized using finite element analyses and optical performance analyses. The optical surface deformations, image qualities, and structure functions for the gravity print-through cases, thermal gradient effects, and dynamic performances were evaluated. The results indicated that the GMT FSM mirror and its support system will favorably meet the optical performance goals for residual surface error and the FSM surface figure accuracy requirement defined by encircled energy (EE80) in the focal plane. The mirror cell assembly analysis indicated an excellent dynamic stiffness which will support the goal of tip-tilt operation.

The Fast-Steering secondary mirror (FSM) of Giant Magellan Telescope (GMT) consists of seven 1.1m diameter segments with effective diameter of 3.2m. Each of the seven segments is held by three axial supports and a central lateral support with a vacuum system to mirror gravity compensations. The mirror assembly has a tip-tilt feature capable of guiding to attenuate telescope wind shake and mount control jitter. Both on-axis and off-axis mirror segments were optimized under various design considerations using finite element analyses and optical performance analyses. An integrated model of the mirror cell assembly was developed including sub-assembly parts consisting of axial supports, lateral support, breakaway mechanism, seismic restraints, and pressure seal. In this paper for the optimized FSM mirror and mirror cell assembly, the design considerations are addressed, and performance prediction results are discussed in detail with respect to the specifications.

The actuator is a primary component of the fast-steering mirror (FSM), and its quality directly determines the performance of FSM. To achieve high compactness, high efficiency, large output torque, and effective linearity, a hybrid reluctance actuator (NHRA) for FSM was designed. To obtain a high-force density and small flux leakage, four permanent magnets (PMs) were designed on the side of the armature, which improves the linearity of the actuator by generating a bias flux. Meanwhile, to obtain the maximum output torque for a limited size, the structural model of the actuator was established in ANSYS Maxwell, and all structural parameters were optimized. In addition, an analytical model of the actuator was established via the equivalent magnetic circuit method. To improve the modeling accuracy, both PM and coil flux leakages were considered. The theoretical and simulation results were insignificant in agreement, and both showed the output torque of this actuator to be approximately twice that of a state-of-the-art actuator under the same volume, simultaneously improving the linearity.

Vibration isolation and precision pointing control will be essential to the success of future space science missions such as Next Generation Space Telescope (NGST). This research investigated the use of actively controlled piezoelectric stack actuators to reduce the transmission of mechanical disturbances to the optics and to coarsely point the telescope. Initial actuator requirements were based on approximate expected motions on the spacecraft side (due to unbalanced reaction wheel assemblies), the structural dynamic properties of the flexible, deployable truss structure that supports the active optics, and the allowable motions on the telescope side. Piezoelectric actuator design was based on flextensional motion amplification, with sizing details determined using results from finite element analysis. A compressive pre-load was maintained on the fragile piezoceramic stacks via a mechanical interference (center block) fit into the actuator frame. Device performance characteristics, including blocked force, passive stiffness, free displacement, motion amplification factor, natural vibration frequencies, and electromechanical coupling coefficient were determined numerically and experimentally, with good agreement. An initial controlled isolation test of the entire system reduced the transmissibility by more than 80% over the frequency range from 4-20 Hz. Finally, an active isolation system with dual sensor feedback was implemented and shown to successfully reduce telescope motion by a factor of 10 (from 4-40 Hz) and to provide lower-frequency pointing capability. Introduction As space systems continue to grow in complexity and require greater precision, piezoelectric materials will be investigated for an increasing number of actuator applications, including precision pointing and vibration isolation and control. There are several approaches to vibration isolation, which have been successful in the past. Vibration isolation can be achieved through passive or active techniques or a combination of the two. The chosen method of isolation depends primarily on the application and requirements of the system. Precision pointing, on the other hand, is achieved solely by active control systems, which combine the necessary structural and mechanical components with a control design. Pointing systems are primarily limited by the quality of the mechanical system as well as the drive system, which is actuating movement. The structure (holding the pay load) to be controlled can be a rigid body, quasi-static flexible body, or a dynamic flexible body. With the classical arrangements of sensors and actuators in these control systems, only the rigid body configuration is commonly controlled. NGST (Next Generation Space Telescope) is the successor to the Hubble Space Telescope (HST) mission. NGST is a deployable 8-meter diameter truss structure holding the telescope and instruments such as cameras and spectrometers that are required by the scientific goals of the mission. In order to meet the scientific goals or projects such as the Origins of Galaxies studies [Mather, et al] along with independent science projects dealing with current scientific interests, positioning the optics and minimizing vibratory loads are very important. Positioning control for the HST was done as a rigid structure pointed as a unit to a precision of a small fraction of an arcsecond, but NGST is a dynamic flexible structure with sub-micron positioning performance. For NGST, the isolation system is to be used to reduce the ultrafine pointing requirements on the fine pointing system (fast steering mirror and adjusters distributed across the mirror) by as much as 1 2 orders of magnitude. This isolation system is aimed to reduce the estimated 30-nm peak disturbances at the mast to 6-nm or less in a range of 4 4 0 Hz, with most concern on the 15 20 Hz region. By substantially reducing these axial disturbances, the dynamic, wavefront error correction requirements will also be reduced, and the fine pointing system will have less of a burden. In order to achieve these requirements, piezoelectric stack actuators are ideal because they can provide sufficiently high output forces with large bandwidths. Individually, piezoelectric stack displacements are extremely small, on the order of approximately 2000 jiie; therefore, multiple stacks can be used in series to produce the desired output. In addition to this, mechanical amplification devices can be used to increase actuation displacement by reducing the actuation force. Compliant mechanisms, flexurehinged mechanisms and flextensional mechanisms Copyright © 2001 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved. (c)2001 American Institute of Aeronautics & Astronautics or Published with Permission of Author(s) and/or Author(s)' Sponsoring Organization. are commonly used for motion amplification, depending on the application. The flextensional actuator used in this research is shown in Figure I and consists of four stacks of piezoceramics connected in parallel to a flextensional mechanism that amplifies and converts the output

The Modular Optical Space Telescope (MOST) project is a design tool that allows rapid generation and analysis of many unique space telescope realizations. The project uses a parametric integrated model to quantitatively analyze many dierent architectures during the conceptual design phase. MOST aims to include advanced concepts and technologies such as lightweight, deformable optics, dynamic wavefront control, and low-cost segmented mirror systems. Traditional optical performance metrics are considered alongside programmatic metrics such as cost, robustness, and mission operations, permitting an examination of these conflicting requirements at the very beginning of the project. The model has been substantially updated to include new technologies, control, and performance metrics, and the trade studies continue to provide insights into determining favorable space telescope architectures. urrent space telescopes are reaching their limits in terms of size, cost, and performance. Future systems will have larger aperatures with increasingly tight performance requirements, with line-of-sight (LOS) jitter on the order of milli-arcseconds and wavefront error (WFE) on the order of nanometers. At the same time, lower mass and lower cost systems are desired. This creates an implicit conflict for currently designed systems, thus new technologies and telescope types must be developed and implemented. Technology possibilities for these new systems include deployable mirrors or sparse apertures, structural control, and active optics. Sparse apertures and deployable optics can be deployed on orbit, eliminating the launch fairing diameter as an aperture size constraint. Also, the smaller, identical mirrors used in sparse apertures are easier and less expensive to manufacture than large monolithic mirrors. Structural control can provide a means to achieve better performance with a less massive system by counteracting the flexible dynamics of the lightweight system. Active optics can help to meet the strict performance requirements. A fast steering mirror can correct for LOS jitter, and wavefront sensing and mirror shape control can rectify both thermal and dynamic distortions of the primary mirror. These and other technologies provide a promising path to meeting both the performance and systematic requirements of future space telescopes. The challenge is in determining which combinations of technologies create favorable architectures. It is important to explore the entire tradespace of possible designs to ensure that superior designs are not overlooked. In order to assist with these important decisions and tradespace exploration, the MOST project has created a parametric modeling technique to consider the implications of design decisions during the conceptual design phase. 1,2 In the past, simple models, along with engineering judgment, have been used in the conceptual design phase where key design decisions were made. During the preliminary design phase, detailed models of the single point design were built and analyzed. If the requirements were not met, then another point design was chosen and modeled. This strategy works well if the system is based upon heritage designs and performance can be adequately predicted. However, with the addition of new technologies, there is no guarantee that the chosen point design would meet the requirements, and if the design does meet requirements, there is no assurance that it is an optimal design. Therefore, the MOST project uses a parameterized model to quickly and automatically generate and analyze many designs during the conceptual

A flexible drive platform performance improvement method based on negative stiffness decoupling and its application in fast steering mirror

The article presents eddy current sensor system in respect to the measurements of vibrations for ultrasonic assisted machining processes. The comparison of eddy current sensor system with laser doppler vibrometer (LDV device) is also presented. The paper concerns the analysis of the influence of the distance between the tool and the sensor on amplitude value, filtering of raw voltage signals in MATLAB and amplitude values presentation for different tools after MATLAB and LDV software analysis. Functionality of two applied devices can be discussed after investigations. Differences in recorded amplitude’s values are also discussed. The examples of measurements and test stand configuration are presented. For better understanding of hybrid machining process, it is important to indicate the possible methods of amplitude measurements and to analyze the results of measurements.

为解决光电跟踪仪跟踪精度测量过程中光束大范围指向的模拟问题，设计了一种大口径、高精度二维快速控制反射镜（fast steering mirror, FSM）。采用微晶材料设计了长、短轴分别为230 mm和160 mm的椭圆形平面反射镜，面形精度优于<i>λ</i>/30。采用音圈电机驱动，通过柔性支撑铰链设计及DSP嵌入式控制系统，运动行程达到±30 mrad，运动控制精度达到5 μrad，运动控制线性度优于±0.20%，角分辨率优于1 μrad。通过软件控制，实现对入射光束圆形轨迹运动、直线轨迹运动、随机运动等形式的运动模拟。最后，对设计指标进行实际测试，可以满足跟踪精度光束动态模拟的测试需求。

Sample-tracking vibration isolation with rigid negative stiffness for broad bandwidth

A simple form of atmospheric tidal theory is used to deduce the dynamic atmospheric response to the nearly periodic 14 month precession of the Earth's rotation axis about its mean position, known as Chandler wobble. The departure of the tide from equilibrium, and the associated horizontal velocity field are calculated for an atmosphere initially at rest and having a constant adiabatic lapse rate with height. Results are in close agreement with those obtained from simple quasi-static approximations to the shallow water equations. The equilibrium tide in surface pressure is small, of order 10−3 mb, for typical polar displacements. The departure of the tide from equilibrium is still smaller, of order 10−6 mb, with associated horizontal velocities of order 10−6 m s−1. Inclusion of a reasonable solid body rotation component in the basic state does not qualitatively alter these results, although the non-equilibrium components are enhanced by nearly an order of magnitude, relative to those for a basic state at rest. The conclusion, qualified by numerous assumptions, is that the atmospheric response in surface pressure and horizontal velocity to the Chandler wobble forcing is of negligible amplitude.