Sensitivity improvement of an optical current sensor with enhancedFaraday rotation

A sensitivity improvement technique is proposed for a class of bulk-glass optical current sensors that employ a ferromagnetic field concentrator. The total effective optical path length is demonstrated theoretically to be an invariant regardless of the bulk glass thickness and consequently independent of the size of the concentrator gap opening. Thus, if the magnetic field is increased by reducing the gap size, the eventual Faraday rotation for a given electric current can be increased proportionally, leading to an improved device sensitivity. The dependence of the gap magnetic field on gap size is calculated with an equivalent circuit model, and this analytical treatment is compared with a dedicated finite element computer package. By taking account of various types of optical power losses present in the bulk glass, the above formulated gap dependence of magnetic field is used to aid a realistic assessment of device sensitivity and this serves as a tool to design and analyze practical bulk-glass optical current sensors. A detailed experimental study to confirm the proposed sensitivity improvement technique is also reported     

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.     

The development of a novel prosthetic hand-ongoing research andpreliminary results

An "ideal" upper limb prosthesis should be perceived as part of the natural body by the amputee and should replicate sensory-motor capabilities of the amputated limb. However, such an ideal "cybernetic" prosthesis is still far from reality: current prosthetic hands are simple grippers with one or two degrees of freedom (DOF), which barely restore the capability of the thumb-index pinch. This paper describes the development of a novel prosthetic hand based on a "biomechatronic" design. The proposed hand is designed to augment the dexterity of traditional prosthetic hands while maintaining approximately the same dimension and weight. Our approach is aimed at providing enhanced grasping capabilities and "natural" sensory-motor coordination to the amputee, by integrating miniature mechanisms, sensors, actuators, and embedded control. A biomechatronic hand prototype with three fingers and a total of six independent DOFs has been designed and fabricated. The paper is focused on the actuators system, which is based on miniature electromagnetic motors     

Development of a magnetic sensing device for tooth displacement under orthodontic forces

We have developed a system for measuring tooth displacement from orthodontic force. Eight small magnetic sensors and a magnet are combined to measure three-dimensional displacement. Sensors, arranged cubically in the three planes of space, are placed in the mouth and fixed to the posterior teeth by a splint. A magnet is placed in the center of the eight sensors and attached to a front tooth that is subjected to orthodontic force. Sensors detect the magnet's movement as target tooth displacement. The system was designed to achieve displacement resolution of 1 microm. The mean percentage of measurement errors was determined to be less than 1% in a 600-cubic-microm volume from calibration. The system was tested clinically on human teeth. Although the oral environment, with high temperature and humidity, was not agreeable with the sensors, this system was stable and accurate enough for quantitative measurement of tooth displacement. The advantage of this system is the ability to detect tooth trajectories by decomposing displacement into translation and rotation and to determine the position of the center of rotation from these parameters.     

Estimation of elbow-induced wrist force with EMG signals using fast orthogonal search

In many studies and applications that include direct human involvement-such as human-robot interaction, control of prosthetic arms, and human factor studies-hand force is needed for monitoring or control purposes. The use of inexpensive and easily portable active electromyogram (EMG) electrodes and position sensors would be advantageous in these applications compared to the use of force sensors, which are often very expensive and require bulky frames. Multilayer perceptron artificial neural networks (MLPANN) have been used commonly in the literature to model the relationship between surface EMG signals and muscle or limb forces for different anatomies. This paper investigates the use of fast orthogonal search (FOS), a time-domain method for rapid nonlinear system identification, for elbow-induced wrist force estimation. It further compares the forces estimated using FOS with the forces estimated by MLPANN for the same human anatomy under an ensemble of operational conditions. In this paper, the EMG signal readings from upper arm muscles involved in elbow joint movement and sensed elbow angular position and velocity are utilized as inputs. A single degree-of-freedom robotic experimental testbed has been constructed and used for data collection, training and validation.     

A Flux-Density-Based Electromagnetic Servo System for Real-Time Magnetic Servoing/Tracking

The goal of this paper is to develop an electromagnetic servo system for two kinds of multiaxis motion control, namely magnetic servoing and magnetic tracking. Based on the proposed space vector expression that is a function of magnetic flux density for estimating the relative position from a magnet to a Hall probe, the magnetic servoing can achieve a contouring control with respect to a fixed magnet, and the magnetic tracking can track a moving magnet. The proposed flux-density-based feedback control is a fully closed-loop scheme, which involves an inner position control loop and an outer magnetic control loop. Experiments are presented to demonstrate the validity of the space vector expression in terms of flux density and the feasibility of the electromagnetic servo system using flux density feedback control.     

Development of the Utah Artificial Arm

The development of a practical multifunction, electronically controlled artificial arm is an extremely complex undertaking. Various technical factors such as the limited capability of man-made components, together with problems in the development of adequate control systems, impair the ultimate performance of any prosthesis. Also, nontechnical problems in clinical, marketing, and economic areas strongly influence the potential success of any system. Consequently, the realization of a practical system with the possibility of near-term application requires simultaneous and coordinated work by personnel in a number of normally unrelated areas of medicine and engineering. The opinions of engineers, physicians, amputees, industrial entities, and institutions responsible for funding the fitting of artificial limnbs must be understood and must influence the design process. This paper begins with a discussion of the natural limb and those design objectives and compromises which govern the development of its artificial counterpart Specific details of the Utah Arm are then reviewed, along with general comments regarding the area of prosthetic limb research and application.     

Acoustic and magnetic surface wave ring interferometers for rotation rate sensing

The similarities and differences between acoustic and magnetic surface waves as compared with light waves are discussed. This comparison suggests several possible advantages of surface wave ring interferometers over optical ring interferometers for rotation sensing. The primary advantags are increased sensitivity, ease of construction, and size reduction. Proposed designs for such sensors are given. In the Appendixes the optical ring interferometer and ring laser are reviewed.     

A micron-sized GMR sensor with a CoCrPt hard bias

A GMR (giant magneto-resistive) spin valve sensor for magnetic recording has been designed in an attempt to solve the Barkhausen noise problem in small-sized GMR sensors. In this study, the GMR ratio of the top-pinned spin valve is optimized to a value of 13.2%. The free layer is magnetized perpendicular to the pinned layer by a CoCrPt permanent magnetic bias so that a linear magnetic field response can be obtained. An obvious improvement on performance is observed when the permanent magnetic bias is magnetized, while the GMR sensor has a steadier MR-H loop and a smaller coercive field.     

基于视觉暂留的动态扫描LED旋转屏

为了研究并控制基于视觉暂留的发光二极管旋转显示屏,在系统仿真研究的基础上,设计并改善了红外驱动电路、磁电传感器电路以及单片机控制系统,在Keil-汇编语言环境下编写了单片机控制程序,制作出PCB电路板并进行了软硬件调试。实验结果表明,设计的基于视觉暂留的发光二极管旋转显示屏具有良好的可控制性和实用性,实现了非矩形及高速旋转场合下的应用。     

Two-DOF magnetic orientation sensor using distributed multipole models for spherical wheel motor

This paper presents a new method for measuring a two degree-of-freedom (DOF) orientation of a permanent magnet (PM) based system using magnetic field measurements. The method exploits distributed multipole (DMP) modeling method to accurately predict a magnetic field, and provides a rational basis to inversely solve for the orientation of the PM from measured data. The PM-based magnetic sensor along with the ability to characterize the magnetic field in real-time offers advantages in sensing and control such as contact-free measurements eliminating frictional wears commonly encountered in existing designs with a combination of single-axis encoders, and high-speed sampling rate thus offering a higher bandwidth than methods based on imaging sensors. This paper demonstrates the efficient method capable of measuring the orientation of the PM by implementing it on a spherical wheel motor (SWM), where the two-DOF orientation is measured. Sensor performance has been studied both analytically and experimentally to validate the DMP-based sensor model. The results can offer valuable insights for optimizing contact-free sensor designs.     

Applied neural control in the 1990s

The authors describe some of the current neural prostheses and examine technological developments needed for future generations of neural prosthetic implants. Current developments include the peroneal nerve stimulator, upper and lower extremity functional neuromuscular stimulation and the auditory prosthesis. Three issues connected with future developments include stimulating and recording electrodes, the interconnection system, encapsulation, the command unit, force, touch, and position sensors, and signal conditioning     

Ambulatory position and orientation tracking fusing magnetic and inertial sensing

This paper presents the design and testing of a portable magnetic system combined with miniature inertial sensors for ambulatory 6 degrees of freedom (DOF) human motion tracking. The magnetic system consists of three orthogonal coils, the source, fixed to the body and 3-D magnetic sensors, fixed to remote body segments, which measure the fields generated by the source. Based on the measured signals, a processor calculates the relative positions and orientations between source and sensor. Magnetic actuation requires a substantial amount of energy which limits the update rate with a set of batteries. Moreover, the magnetic field can easily be disturbed by ferromagnetic materials or other sources. Inertial sensors can be sampled at high rates, require only little energy and do not suffer from magnetic interferences. However, accelerometers and gyroscopes can only measure changes in position and orientation and suffer from integration drift. By combing measurements from both systems in a complementary Kalman filter structure, an optimal solution for position and orientation estimates is obtained. The magnetic system provides 6 DOF measurements at a relatively low update rate while the inertial sensors track the changes position and orientation in between the magnetic updates. The implemented system is tested against a lab-bound camera tracking system for several functional body movements. The accuracy was about 5 mm for position and 3 degrees for orientation measurements. Errors were higher during movements with high velocities due to relative movement between source and sensor within one cycle of magnetic actuation.     

槽楔材料对PMLSM电磁特性的影响

为提高PMLSM的电磁性能并降低齿槽力和推力波动,文中提出一种在直线电机槽口安装槽楔的解决方案。槽楔材料对电机性能影响较大,为了使电磁性能最佳,文中以分数槽永磁直线同步电机为研究对象,分析了槽楔材料为硬磁、软磁和非磁时对电机气隙系数的影响。利用有限元法对比分析了3种槽楔材料下电机的气隙磁场、反电动势、齿槽力和推力波动等电磁性能,并对不同负载下削弱推力波动的程度进行对比。分析结果表明,硬磁性材料可以有效降低齿槽力和推力波动。最后研究了不同相对磁导率下硬磁性材料对电机性能的影响,并得到电机性能最佳时的相对磁导率值,为进一步提高电机性能提供了理论基础。     

An application of magnet and magnetic sensor: measurement systemfor tooth movement

A system for measuring tooth displacement and rotation in the sagittal and frontal planes was designed and tested. Four small magnetic sensors were arranged at each corner of a rectangular on a plastic sheet. They were then placed in the mouth and fixed to the front teeth with a plastic splint. A powerful magnet made of a rare earth metal was fixed to the target tooth and placed at the center of the sensors. Movement of the magnet was detected by the four sensors as the tooth trajectory. This system was tested by measuring first molar movement in human subjects with a load generated by an orthodontic aid. The system was small enough to fit in a human oral cavity and did not interfere with the orthodontic aid. Although the high humidity and high temperature of the oral environment were not agreeable for the sensors, resolution was estimated at better than 3μm, including the effects of system drift. The advantage of this system is not only the two-dimensional measurement, but also the rotational measurement, in which a 0.05° resolution was calculated     

Magnetic Field Measurement System in Superconducting Combined Function Magnets for the J-PARC Neutrino Beam Line

Magnetic field measurements have been performed for the first full-scale magnet system assembled with the cryostat for the J-PARC proton beam line of neutrino experiment. In the measurement system, the probe position with respect to magnet central axis is measured by a Helium Neon laser and a position sensitive detector, PSD, in order to obtain an exact dipole field strength. Errors associated with the PSD misalignment and influences on the PSD signals by the magnetic field were evaluated. The measured dipole components approached to the design values by compensating those with the probe position. The latest beam simulation indicated that the measured values of magnetic field were good enough for the primary proton beam transport.     

Theory of magnetostatic waves in moving ferrite films andapplications to rotation rate sensing

A first-order field theory for electromagnetic waves in moving ferrites and ferrite thin films is presented. The dominant effect of the motion is found to be the Doppler-shifted frequency observed in the moving frame. This gives rise to an anomalously large shift in wavenumber, due to the dispersive nature of the ferrite medium. Because of the large effect, it is suggested that a moving-medium experiment using magnetostatic waves could be used to distinguish between various competing forms for the dispersion term in the Fresnel-Fizeau coefficient. The results of the field theory are discussed with relation to relative and absolute rotation rate sensing. The author describes how magnetostatic waves could be used to measure relative rotation rates if confined to propagate around the perimeter of a rotating disk. Since the phase shift would be established in the time required to propagate around the disk, the response time could be significantly shorter than conventional tachometers. An experiment with counterpropagating magnetostatic waves is suggested to clarify the effect of a magnetic medium on the magnitude of the Sagnac effect     

基于小周期永磁型错列波荡器的紧凑型XFEL装置设计

X射线自由电子激光(XFEL)装置具有规模庞大、造价高昂的缺点,因此XFEL装置小型化成为该领域一个重要的研究方向,减小波荡器周期是小型化XFEL装置的重要手段之一。小周期永磁型错列波荡器周期可做到10 mm,同时产生约0.8 T的峰值磁场,在小型化XFEL装置上具有潜在应用价值。本文将小周期永磁型错列应用到SASE型XFEL装置中,分析了纵向磁场对起振过程和辐射性能可能的影响,设计了一台辐射波长1 nm的SASE型XFEL装置并计算了其辐射性能,峰值功率约2.2 GW,单脉冲能量约2.4μJ。通过本文证明了小周期永磁型错列波荡器在缩减基于加速器光源规模上的作用。     

RKA 引导磁场设计研究

本文为RKA 设计了一套秒级脉冲磁场系统,该系统主要由磁场线圈和磁场电源两部分组成,磁场线圈通过迭代 获得所需截面形状,之后进行了必要的电磁参数设计,对与之配套的磁场电源提出了主要技术要求和时序控制问题。最 后初步测试了RKA 磁场位形情况,经测试,该秒级脉冲磁场性能稳定,满足RKA 磁场约束要求。     

Redundancy resolution of the human arm and an upper limb exoskeleton

The human arm has 7 degrees of freedom (DOF) while only 6 DOF are required to position the wrist and orient the palm. Thus, the inverse kinematics of an human arm has a nonunique solution. Resolving this redundancy becomes critical as the human interacts with a wearable robot and the inverse kinematics solution of these two coupled systems must be identical to guarantee an seamless integration. The redundancy of the arm can be formulated by defining the swivel angle, the rotation angle of the plane defined by the upper and lower arm around a virtual axis that connects the shoulder and wrist joints. Analyzing reaching tasks recorded with a motion capture system indicates that the swivel angle is selected such that when the elbow joint is flexed, the palm points to the head. Based on these experimental results, a new criterion is formed to resolve the human arm redundancy. This criterion was implemented into the control algorithm of an upper limb 7-DOF wearable robot. Experimental results indicate that by using the proposed redundancy resolution criterion, the error between the predicted and the actual swivel angle adopted by the motor control system is less then 5°.