Closed-loop magnetic bearing and angular velocity control of a reaction sphere actuator

This article presents the first closed-loop magnetic bearing and angular velocity experimental results of a reaction sphere actuator for satellite attitude control. The proposed reaction sphere is a permanent magnet spherical actuator whose rotor is supported by magnetic bearing and can be torqued electronically about any desired axis. The spherical actuator is composed of an 8-pole permanent magnet spherical rotor and of a 20-pole stator with electromagnets. The electromechanical model of the reaction sphere is summarized together with procedures to estimate the rotor magnetic state, the back-EMF voltage, and the rotor angular velocity, which are all fundamental ingredients for controller design. Dynamic controllers are developed to levitate the rotor inside the stator (magnetic bearing) and to control the rotor angular velocity. The magnetic bearing is based on a state-space controller with reduced-order displacement velocity estimator whereas the angular velocity controller is a simple proportional controller with a dedicated angular velocity estimator. The developed control algorithms are experimentally validated using the developed laboratory prototype showing the ability of simultaneously levitating the rotor while rotating it about a given arbitrary axis.     

转轴转角定位误差测量方法与误差分析

提出了一种基于光纤激光自准直转轴转角定位误差测量的方法,建立了包含转轴运动误差以及安装误差的误差模型,仿真分析了23项误差对转角定位误差测量的影响,结果表明仅有参考转轴与待测转轴之间的4项安装误差的影响量与转轴旋转角度相关,且只需精细调整其中两项角度安装误差即可保证影响量小于0.2。利用所搭建的测量装置对某分度盘的转角定位误差进行了测量,三次测量重复性偏差约为0.9,与光电自准直仪对比的最大偏差约为0.6。结果表明:利用该测量方法和测量装置可以实现转轴转角定位误差的全周范围高精度测量,验证了所提出模型的有效性。     

量子衍生差分进化算法的设计与实现

为提高差分进化算法的优化性能,从研究差分进化算法的实现机制入手,提出将差分策略与量子比特在Bloch球面的绕轴旋转相融合的新思想。个体采用基于Bloch球面描述的量子比特编码,采用差分策略计算当前个体上量子比特的旋转角度,采用向量积理论构造旋转轴,采用泡利矩阵构造旋转矩阵,以当前最优个体上相应量子比特为目标,在Bloch球面上沿旋转轴向目标比特旋转。采用Hadamard门实现个体变异。函数极小值优化的仿真结果表明,所提方法单步迭代的平均时间约为普通差分进化算法的13倍。当限定步数相同时,优化结果约为普通差分进化算法的0.3倍,当运行时间相同时,优化结果约为普通差分进化算法的0.4倍。从而表明所提算法计算效率降低,但寻优能力明显提高,整体优化性能优于原算法。      

Volume Registration Using the 3-D Pseudopolar Fourier Transform

This paper introduces an algorithm for the registration of rotated and translated volumes using the three-dimensional (3-D) pseudopolar Fourier transform, which accurately computes the Fourier transform of the registered volumes on a near-spherical 3-D domain without using interpolation. We propose a three-step procedure. The first step estimates the rotation axis. The second step computes the planar rotation relative to the rotation axis. The third step recovers the translational displacement. The rotation estimation is based on Euler's theorem, which allows one to represent a 3-D rotation as a planar rotation around a 3-D rotation axis. This axis is accurately recovered by the 3-D pseudopolar Fourier transform using radial integrations. The residual planar rotation is computed by an extension of the angular difference function to cylindrical motion. Experimental results show that the algorithm is accurate and robust to noise.     

Chronic whiplash associated disorders and neck movement measurements: an instantaneous helical axis approach

This paper presents an assessment tool for objective neck movement analysis of subjects suffering from chronic whiplash-associated disorders (WAD). Three-dimensional (3-D) motion data is collected by a commercially available motion analysis system. Head rotation, defined in this paper as the rotation angle around the instantaneous helical axis (IHA), is used for extracting a number of variables (e.g., angular velocity and range, symmetry of motion). Statistically significant differences were found between controls and subjects with chronic WAD in a number of variables.     

Hybrid learning control schemes with input shaping of a flexible manipulator system

The paper describes a practical approach to investigate and develop a hybrid iterative learning control scheme with input shaping. An experimental flexible manipulator rig and corresponding simulation environment are used to demonstrate the effectiveness of the proposed control strategy. A collocated proportional-derivative (PD) controller utilizing hub-angle and hub-velocity feedback is developed for control of rigid-body motion of the system. This is then extended to incorporate iterative learning control with acceleration feedback and genetic algorithms (GAs) for optimization of the learning parameters and a feedforward controller based on input shaping techniques for control of vibration (flexible motion) of the system. The system performance with the controllers is presented and analysed in the time and frequency domains. The performance of the hybrid learning control scheme with input shaping is assessed in terms of input tracking and level of vibration reduction. The effectiveness of the control schemes in handling various payloads is also studied.     

Automatic correction of motion artifacts in magnetic resonanceimages using an entropy focus criterion

Presents the use of an entropy focus criterion to enable automatic focusing of motion corrupted magnetic resonance images. The authors demonstrate the principle using illustrative examples from cooperative volunteers. Their technique can determine unknown patient motion or use knowledge of motion from other measures as a starting estimate. The motion estimate is used to compensate the acquired data and is iteratively refined using the image entropy. Entropy focuses the whole image principally by favoring the removal of motion induced ghosts and blurring from otherwise dark regions of the image. Using only the image data, and no special hardware or pulse sequences, the authors demonstrate correction for arbitrary rigid-body translational motion in the imaging plane and for a single rotation. Extension to three-dimensional (3-D) and more general motion should be possible. The algorithm is able to determine volunteer motion well. The mean absolute deviation between algorithm and navigator-echo-determined motion is comparable to the displacement step size used in the algorithm. Local deviations from the recorded motion or navigator-determined motion are explained and the authors indicate how enhanced focus criteria may be derived. In all cases they were able to compensate images for patient motion, reducing blurring and ghosting     

Modeling of prosthetic limb rotation control by sensing rotation of residual arm bone

We proposed a new approach to improve the control of prosthetic arm rotation in amputees. Arm rotation is sensed by implanting a small permanent magnet into the distal end of the residual bone, which produces a magnetic field. The position of the bone rotation can be derived from magnetic field distribution detected with magnetic sensors on the arm surface, and then conveyed to the prosthesis controller to manipulate the rotation of the prosthesis. Proprioception remains intact for residual limb skeletal structures; thus, this control system should be natural and easy-to-use. In this study, simulations have been conducted in an upper arm model to assess the feasibility and performance of sensing the voluntary rotation of residual humerus with an implanted magnet. A sensitivity analysis of the magnet size and arm size was presented. The influence of relative position of the magnet to the magnetic sensors, orientation of the magnet relative to the limb axis, and displacement of the magnetic sensors on the magnetic field was evaluated. The performance of shielding external magnetostatic interference was also investigated. The simulation results suggest that the direction and angle of rotation of residual humerus could be obtained by decoding the magnetic field signals with magnetic sensors built into a prosthetic socket. This pilot study provides important guidelines for developing a practical interface between the residual bone rotation and the prosthesis for control of prosthetic rotation.      

MagTable: A tabletop system for 6-DOF large range and completely contactless operation using magnetic levitation

This paper presents a new magnetic levitation system, MagTable, which provides six-degrees-of-freedom (6-DOF) and completely contactless operation of a magnetized object. The MagTable consists of a planar array of square coils and a permanent magnet type carrier. The maximum levitation height of the carrier is 30mm within a 400mm × 200mm horizontal translation range. The novelty of this research lies in the fully untethered manipulation of levitated carriers in such a large area, and in the fast and accurate computation of wrench matrix using the magnetic nodes method and the Lorentz force law. In this paper, the design method is firstly provided. Then, the optimization of the carrier's magnet topology, based on better controllability and minimum power consumption, is documented. Experimental results of the 5-DOF motion control of two single-permanent-magnet carriers and the 6-DOF motion control of a three-permanent-magnets carrier are presented. The results demonstrate the performance of the MagTable in 100mm × 40mm horizontal translation range with maximum levitation height of 20mm. The rotation range are ±6° in both roll and pitch, and ±12° yaw motion about the vertical axis. The proposed system has potential applications in fast and high precision manipulation tasks.     

压电振动微机械陀螺研究

本文介绍了一种新型的压电振动微机械陀螺，与其它大多数压电陀螺不同，它不需要弹性元件，由压电材料本身构成振子完成陀螺功能，由ＰＺＴ薄膜材料做成的平板沿厚度方向极化并受电激励产生厚度伸缩振动，当一输入角速度作用于振子，根据哥氏效应，则在极化轴和输入角速度轴组成的闰面垂直方向上产生一正比于输入的速度大小的感应电压，它是一种双轴陀螺，本文给出了它的物理模型，并用ＰＺＴ陶瓷晶体做了宏观模拟实验，实验结果与理     

Accuracy in Prediction of Catheter Rotation in IVUS With Feature-Based Optical Flow—A Phantom Study

The quantitative assessment of and compensation for catheter rotation in intravascular ultrasound images presents a fundamental problem for noninvasive characterization of the mechanical properties of the coronary arteries. A method based on the scale-space optical flow algorithm with a feature-based weighting scheme is proposed to account for the aforementioned artifact. The computed vector field, describing the misalignment between two consecutive frames, allows the quantitative assessment of the amount of vessel wall tissue motion, which is directly related to the catheter rotation. Algorithm accuracy and robustness were demonstrated on two tissue-mimicking phantoms, subjected to controlled amount of angular deviation. The proposed method shows a great reliability in the prediction of catheter rotational motion up to 4deg.     

基于MEMS传感器的微飞行器姿态理论与实验研究

为了得到基于微机电系统(MEMS)运动传感器的微飞行器的姿态角的输出,该文从理论和实验角度进行了全面分析。首先基于MEMS运动传感器的加速度计与磁力计理论计算了微飞行器的初始姿态及其最大误差范围,然后基于MEMS运动传感器的陀螺仪计利用时间序列自回归滑动平均模型(ARMA)分析方法对原始角速度进行误差建模,并利用卡尔曼滤波进行误差补偿,并通过积分法到更高精确度的姿态角度的算法,最后利用转台实验对其进行验证。通过该算法,对于任何MEMS九轴传感器,由实验确定相应的参数后,即可得到该传感器更高精确度的姿态角的输出。     

The Problem of Electromagnetic Field Diffraction by an Axisymmetric Inhomogeneous Body

An approximate method is proposed for the solution of the vector problem of diffraction by a body of revolution. The material characteristics of the body are independent of the angular coordinate in the cylinder coordinate frame. The method is tested using the problem of diffraction of a plane wave by a sphere and a circular cylinder having finite dimensions. The rigorous approach based on a spline basis is used in the case of a dielectric sphere whose wavenumber depends only on the radial coordinate (in spherical coordinates). The two methods are compared for the case of the parabolic dependence of the squared wavenumber of an inhomogeneous sphere on the radial coordinate. The diffraction of a point source field by a metamaterial inhomogeneous sphere is considered.     

Structure of energy quantum levels in a quantum dot shaped as an oblate body of revolution

It was shown that the electron energy spectrum in a disk-shaped potential well is characterized by two types of levels. One is characterized by a quantum number corresponding to carrier motion mainly along the disk axis. Energy intervals between such levels are large. As a rule, only a single electron level of this type can fit into the InAs quantum dot with GaAs surroundings. The second-type levels form a substructure with quantum numbers corresponding to carrier rotation about the polar axis and motion along the major disk axis. The distances between such levels are rather short. The theory makes it possible to determine the number of such levels as a function of the disk thickness and diameter and the conditions of the quantum dot transition into the quantum well with a large number of substructure levels.     

Data-based spatial feedforward for over-actuated motion systems

For advanced motion systems there is an increasing demand for higher production throughput and accuracy. Traditionally, such systems are designed using a rigid-body design paradigm, which aims at designs with high stiffness. The alternative is to design a lightweight system and deal with the resulting flexibilities by over-actuation and over-sensing. This paper presents a data-based spatial feedforward method based on previous task trials, which aims at reducing the vibrations over the complete structure during motion. The proposed method is experimentally validated on an industrial prototype and compared to standard mass feedforward using rigid-body decoupling.     

基于涡旋电磁波体制的三维SAR成像方法

涡旋电磁波得名于其传播时围绕行进轴的旋转现象,该电磁属性被称为轨道角动量。基于其在方位角上的目标分辨能力,该文将涡旋电磁波引入传统的合成孔径成像中,提出了一种新的三维成像方案。在结合轨道角动量模态域之后,将合成孔径雷达二维回波扩展到三维。首先,基于波形分集理论,获取同时多模态回波数据,并利用傅里叶变换(FT)变换到方位角维,形成距离-合成孔径方位-方位角三维数据。然后,基于Radon-FT,提出了一种联合二维方位压缩算法来生成三维目标成像。仿真结果验证了系统和算法的性能,证明了涡旋电磁三维合成孔径成像雷达系统的优越性。      

A magnetic flux model based method for detecting multi-DOF motion of a permanent magnet spherical motor

This paper presents a new method, referred to here as back-EMF method, for sensing the multi-DOF motion of a permanent magnet spherical motor (PMSM). With an explicit model characterizing the magnetic flux in the PMSM, a relationship between the electromotive force (EMF) induced in the winding of electro-magnets and the motion of the rotor permanent magnets is derived; and closed-form solutions that solves for multi-DOF Euler angles and angular velocities of the rotor are presented. This method allows for simultaneous estimation of both quantities in real-time by only measuring the voltages across the electro-magnets. Requiring no installation of additional sensors or fixtures on the rotor, the back-EMF method retains the structural simplicity of the PMSM. This method has been experimentally investigated on a prototype PMSM; the estimated Euler angles and angular velocities compare favorably with measurements from a commercialized gyroscope. As an immediate application, the motion states acquired using the back-EMF method are used for parameter estimation of the PMSM.     

Fast eigenspace decomposition of correlated images

We present a computationally efficient algorithm for the eigenspace decomposition of correlated images. Our approach is motivated by the fact that for a planar rotation of a two-dimensional (2-D) image, analytical expressions can be given for the eigendecomposition, based on the theory of circulant matrices. These analytical expressions turn out to be good first approximations of the eigendecomposition, even for three-dimensional (3-D) objects rotated about a single axis. In addition, the theory of circulant matrices yields good approximations to the eigendecomposition for images that result when objects are translated and scaled. We use these observations to automatically determine the dimension of the subspace required to represent an image with a guaranteed user-specified accuracy, as well as to quickly compute a basis for the subspace. Examples show that the algorithm performs very well on a number of test cases ranging from images of 3-D objects rotated about a single axis to arbitrary video sequences.     

基于角谱插值的数字全息在任意斜面的重建方法

为了在任意非平行斜面上重建数字全息像,提出了一种基于角谱旋转变换和插值的数字处理方法,用角谱衍射理论进行了分析,给出了正反旋转两种数字插值方法,基于旋转变换信息量不变的原则分析了倾斜面上的抽样间隔取值范围,其大小取决于斜面带宽和全息图空间带宽积大小。实现了在71°倾斜物面上的全息重建,消除了倾斜造成的局部离焦现象,同时验证了算法在斜面上抽样间隔取值范围。     

Magnetic levitation with unlimited omnidirectional rotation range

We have realized a magnetic levitation device in which the motion of a levitated body can be stably controlled in any orientation, with no limits on its spatial rotation range. The system consists of a planar array of cylindrical coils on a fixed base, a levitated frame containing disc magnets and LED position markers, and an optical motion tracking sensor for feedback control of levitation. This system combines the capabilities of fine positioning, vibration isolation, and a spherical motor, with potential applications in omnidirectional antenna and camera pointing, user interaction, manipulation, and simulated spaceflight dynamics and control. The device design is presented including the magnet and coil configuration, analysis and control methods, and position and rotation trajectory control results.The system development process consisted of numerical analysis of electromagnetic forces and torques between coils and magnets, to find the maximum required coil currents for levitation and the condition numbers of the transformation matrices between coil currents and forces and torques generated on the levitated body, for various configurations of coils and magnets, over their full 3D translation and rotation ranges. As a result, a magnetic levitation setup consisting of an array of 27 coils and a levitated object with six disk-shaped permanent magnets was selected. The setup achieved levitation in six degrees of freedom and unlimited rotation about any axis at a fixed height of 40 mm (a 4 mm minimum height above the coil array). The performance was verified with levitated trajectory following rotation command experiments in roll, pitch, yaw, and including 360° rotations about non-principal axes.