Design Considerations for a Real-Time Ocular Counterroll Instrument

A video-based technique for measuring the torsional movement of the eye (counterroll) by processing video images of the eyeball is presented. Spectral estimates show that most of the variance of the iris image is in the angular direction. It will be demonstrated that cross correlation between sequences that are obtained by circular sampling of the digitized image of the iris is sufficient to extract the counterroll information. Computation time for angular correlation is thus significantly reduced and real-time hardware implementation becomes feasible. As the result of a preprocessing step, we obtain the information about the horizontal and vertical movement of the eye and also the diameter of the pupil. To improve the measurement resolution, a fast second degree local least square interpolation of the cross-correlation function is used. Possible sources of error and the limitations of the algorithm will be studied. The results of the computer simulations made using the algorithm serve to experimentally confirm the error estimates. Application of the algorithm to photographically obtained image data from human subjects demonstrates its practicality on normal eyes. The system design for a device for measuring 3D movement of the eye will be discussed.     

Combined head and eye tracking system for dynamic testing of thevestibular system

The authors present a combined head-eye tracking system suitable for use with free head movement during natural activities. This system provides an integrated head and eye position measurement while allowing for a large range of head movement (approx 1.8 m of head translation is tolerated). Six degrees of freedom of head motion and two degrees of freedom of eye motion are measured by the system. The system was designed to be useful for the evaluation of the vestibulo-ocular reflex (VOR). The VOR generates compensatory eye movements in order to stabilize gaze during linear or rotational motion of the head. Current clinical and basic research evaluation of the VOR has used a restricted range of head motion, mainly low-frequency, yaw rotation. An integrated eye-head tracking system such as the one presented here allows the VOR response to linear and angular head motion to be studied in a more physiologically relevant manner. Two examples of the utility of the integrated head and eye tracking system in evaluating the vestibular response to linear and angular motion are presented     

Galvanic vestibular stimulation elicits consistent head-neck motion in seated subjects

Humans actively stabilize the head-neck system based on vestibular, proprioceptive and visual information. Galvanic vestibular stimulation (GVS) has been used previously to demonstrate the role of vestibular feedback in standing balance. This study explores the effect of GVS on head-neck kinematics and evaluates the approach to investigate the vestibular contribution to head-neck stabilization. GVS was applied to 11 seated subjects using seven different stimuli (single sinusoids and multisines) at amplitudes of 0.5-2 mA and frequencies of 0.4-5.2 Hz using a bilateral bipolar configuration while 3-D head and torso kinematics were recorded using motion capture. System identification techniques were used evaluating coherence and frequency response functions (FRFs). GVS resulted in significant coherence in roll, yaw and lateral translation, consistent with effects of GVS while standing as reported in the literature. The gain of the FRFs varied with frequency and no modulation was observed across the stimulus amplitudes, indicating a linear system response for the stimulations considered. Compared to single sine stimulation, equivalent FRFs were observed during unpredictable multisine stimulation, suggesting the responses during both stimuli to be of a reflexive nature. These results demonstrate the potential of GVS to investigate the vestibular contribution to head-neck stabilization.     

Galvanic vestibular stimulation for analysis of postural adaptationand stability

Human postural dynamics was investigated in 12 normal subjects by means of a force platform recording body sway, induced by bipolar transmastoid galvanic stimulation of the vestibular nerve and labyrinth. The model adopted was that of an inverted segmented pendulum, the dynamics of postural control being assumed to be reflected in the stabilizing forces actuated by the feet as a result of complex muscular activity subject to state feedback of body sway and position. Time-series analysis demonstrates that a transfer function from stimulus to sway-force response with specific parameters can be identified. In addition, adaptation to the vestibular stimulus is demonstrated to exist, and the authors describe this phenomenon using quantification in terms of a postural adaptation time constant in the range of 40-50 s. The results suggest means to evaluate adaptive behavior and postural control in the erect human being which may be useful in the rehabilitation of individuals striving to regain upright stance     

仿生角加速度传感器设计及传感特性研究

半规管是人体前庭系统中的一种角位移感知器官,该文基于人体半规管几何尺寸、机械属性及内部结构,利用表面对称电极含金属芯聚偏二氟乙烯(PVDF)纤维(SMPF)传感器,设计制备了一种结构尺寸、工作机理与人体半规管基本一致的仿生角加速度传感器。同时搭建了实验系统,对仿生半规管传感器的感知理论模型进行了验证。实验结果证明,传感器的工作机理与数学模型推导结果基本一致,仿生传感器在不同加速度刺激下输出相应幅值的电信号。通过扫频实验确认系统固有频率约为10 Hz,可用于人体头部的运动检测。     

Noninvasive optical polarimetric glucose sensing using a true phasemeasurement technique

The focus of this paper was to describe the development and testing of a noninvasive true phase optical polarimetry sensing system to monitor in vivo glucose concentrations. To demonstrate the applicability of this optical sensor for glucose measurement, we first calibrated the system and then tested it in vitro using both a glass test cell filled with glucose solution in the physiologic range, with a path length of 0.9 cm to approximate one centimeter path length present in the anterior chamber of the eye, and then on an excised human eye. Our technique used helium neon laser light which was coupled through a rotating linear polarizer along with two stationary linear polarizers and two detectors to produce reference and signal outputs whose amplitudes varied sinusoidally with a frequency of twice the angular velocity of the rotating polarizer, and whose phase was proportional to the rotation of the linear polarization vector passing through the glucose solution.     

Channel Sounding System for MM-Wave Bands and Characterization of Indoor Propagation at 28 GHz

The aim of this work is to present a vector network analyzer based channel sounding system capable of performing measurements in the range from 2 to 50 GHz. Further, this paper describes an indoor measurement campaign performed at 26–30 GHz. The sounding system is capable of receiving two channels and transmitting one. Using this feature a channel measurement has been performed using both a directional horn antenna and a virtual uniform circular array (UCA) at the same time. This allows for comparative studies of measured channels with two different antennas in a simultaneous way. The measurement has been conducted with 42 measurement positions distributed along a 10 m long path through an indoor laboratory environment. The transmitter was positioned such that measurements were conducted both in line-of-sight and non-line-of-sight scenarios. The measurements showed good agreement between the measurement data collected with the horn antenna and the data collected with the UCA. The propagation environment was found to be sparse both in delay and angular domain for the given scenario. Based on the performed measurement campaign together with validation measurements of the system stability, it is found that the system works as expected.     

模式识别和电视跟踪在前庭功能检查中的应用

应用模式识别和电视跟踪原理测量眼球在视靶信号刺激下的运动,为分析飞行员、车辆驾驶员的前庭功能提供一种先进的检查方法.采用均衡化、形态滤波和形心计算等方法实现了瞳孔区域的自动定位和实时跟踪;通过Harris角点检测和Lucas-Kanade光流跟踪实时测量出虹膜的旋转角度,为前庭功能分析奠定了良好的基础.通过实验验证,所介绍的眼球跟踪算法已达到了预期的效果,并已成功应用在前庭功能检查分析系统中.     

基于稀疏采样的空间碎片群目标成像方法

低重频、短数据条件下的雷达成像是比较困难的,同时,星载平台观测的碎片目标多以群目标形式出现。针对窄带条件下的空间碎片群目标成像问题,该文提出了一种基于稀疏重构的空间碎片群目标成像方法。由于空间碎片通常存在高速自旋现象,且碎片之间因质量、密度等物理差异存在明显的转速差,利用观测时间内碎片群的多周期观测数据与转速差异性,结合回波的自相关特性,能有效实现碎片群的转速检测。由于碎片在空域具有强稀疏特性,结合碎片转速,利用观测矩阵抽取数据,可以实现等效插值操作,并且将稀疏重构得到的数据进行重排,即可得到各个目标的像。抽取操作能够一定程度地抑制其他碎片的回波能量,并解决在低重频条件下的多普勒模糊问题。理论分析证明了该文所提方法的有效性,仿真实验表明,该文所提方法能够在低重频条件下实现对碎片群目标的分别成像。      

Shoulder and elbow joint angle tracking with inertial sensors

Wearable inertial systems have recently been used to track human movement in and outside of the laboratory. Continuous monitoring of human movement can provide valuable information relevant to individuals' level of physical activity and functional ability. Traditionally, orientation has been calculated by integrating the angular velocity from gyroscopes. However, a small drift in the measured velocity leads to increasing integration error over time. To compensate that drift, complementary data from accelerometers are normally fused into tracking systems using the Kalman or extended Kalman filter. In this study, we combine kinematic models designed for control of robotic arms with state-space methods to continuously estimate the angles of human shoulder and elbow using two wearable inertial measurement units. We use the unscented Kalman filter to implement the nonlinear state-space inertial tracker. Shoulder and elbow joint angles obtained from 8 subjects using our inertial tracker were compared to the angles obtained from an optical-tracking reference system. On average, there was an RMS angle error of less than 8 (°) for all shoulder and elbow angles. The average correlation coefficient for all movement tasks among all subjects was r ≥ 0.95 . This agreement between our inertial tracker and the optical reference system was obtained for both regular and fast-speed movement of the arm. The same method can be used to track movement of other joints.     

MICROCOMPUTERIZED MEASUREMENT AND ANALYSIS OF ELECTRON EMISSION PROPERTIES OF THERMIONIC CATHODES

A microcomputerized measurement system is developed.This system automatically acquiresan I-V characteristic curve in 5 seconds with the accuracy of 0.05％ FSR(full scale range).The Schottkyextrapolation field-free emission,the inflection-point emission,the flection-point emission,the average effec-tive work function.the Richardson work function,the work function distribution at the operation tempera-ture and other important information that reflects properties of cathodes are obtained by this system.The re-sults of analysing four types of cathodes demonstrate that this system is very suitable for measuring the activi-ty changes of the cathode in the processes of activation,ageing,poisoning and life test.It is proved that thissystem can also be used to monitor the actlvity of the cathode in the assembled tube by measuring a gridcontrolled travelling-wave tube.     

Development of a totally active magnetically suspended gyro

A magnetically suspended gyro (MSG) is developed and its performances is estimated. In the MSG, a disk-type rotor is connected to a synchronous motor through a fluid bearing and the motor is fixed to the frame of the floator. The floator is suspended by magnetic force without any mechanical contact so that highly accurate measurement is possible. In accordance with this concept, a three-degrees-of-freedom (DOF) active MSG was developed. However, because of poor damping in the passive suspension and the low resolution of the displacement sensors, the measurement accuracy was relatively low. To solve these problems, a six-DOF (totally) active MSG is designed and fabricated. The frame of this gyro is an octagonal. The motion of the frame is controlled by eight electromagnets. The performance of the gyro is evaluated through measurement of the double-axis angular velocity. The advantages of totally active suspension are investigated. Sufficient damping rapidly reduces the influence of disturbances. Then, the influence of sensor noise is examined. The results of this examination show that the accuracy of the angular velocity measurement is improved by using highly sensitive displacement sensors. Next, the dynamic range is measured. This experiment shows that the MSG can provide precise angular velocity measurement in a low-frequency region.     

Quantification of force abnormalities during passive andactive-assisted upper-limb reaching movements in post-stroke hemiparesis

We evaluated a method for measuring abnormal upper-limb motor performance in post-stroke hemiparetic subjects. A servomechanism (MIME) moved the forearm in simple planar trajectories, directly controlling hand position and forearm orientation. Design specifications are presented, along with system performance data during an initial test of 13 stroke subjects with a wide range of impairment levels. Performance of subjects was quantified by measuring the forces and torques between the paretic limb and the servomechanism as the subjects relaxed (passive), or attempted to generate force in the direction of movement (active). During passive movements, the more severely impaired subjects resisted movement, producing higher levels of negative work than less-impaired subjects and neurologically normal controls. During active movements, the more severely impaired subjects produced forces with larger directional errors, and were less efficient in producing work. These metrics had significant test-retest repeatability. These motor performance metrics can potentially detect smaller within-subject changes than motor function scales. This method could complement currently used measurement tools for the evaluation of subjects during recovery from stroke, or during therapeutic interventions.     

基于ADNS2610的微型飞机速度检测系统设计

设计了以ADNS2610光学传感器为核心的微型飞机水平飞行速度测量系统。该系统使用光流法进行测速,通过透镜将地表图像聚焦到ADNS光学传感器的感光面,利用传感器内置的信号处理单元判断图像的运动方向和距离。微处理器MSP430F449根据图像运动距离的检测周期和微型飞机的飞行高度,计算出微型飞机的水平飞行速度。该系统可以在微型飞机近地飞行时发挥作用,测量时对地角速度最大可达76．2rad／s。     

Feedback control of coronal plane hip angle in paraplegic subjectsusing functional neuromuscular stimulation

This paper reports on an investigation of feedback control of coronal plane posture in paraplegic subjects who stand using functional neuromuscular stimulation (FNS). A feedback control system directed at regulating coronal plane hip angle in neutral position was designed, implemented, and evaluated in two paraplegic subjects. The control system included sensor mounting and signal processing techniques, a two-stage feedback controller, stimulation hardware, and a set of percutaneous intramuscular electrodes. The feedback controller consisted of two-stages in cascade: a modified discrete-time proportional-integral-derivative (PID) stage and a nonlinear single-input, multiple-output stage to determine the stimulation to be sent to several muscles. The focus of this work was on evaluating the performance of the feedback controller by comparing the response of the feedback-controlled system to that of an open-loop stimulation system. In an evaluation based on temporal response characteristics the controlled system exhibited a 41% reduction in root-mean-squared (rms) error (where error is defined as the deviation from the desired angle), a 52% reduction in steady-state error, and a 22% reduction in hip compliance. In addition, the feedback-controlled system exhibited significant reductions in variability of these measures on several days. These results demonstrate the ability of the feedback controller to improve the temporal response characteristics of the FNS control system.     

Characterizing Fiber Bragg Grating Index Profiles to Improve the Writing Process

We demonstrate an accurate method for identifying both systematic and random errors in a fiber Bragg grating (FBG) writing system and show its application to calibration of the writing process. We first measure the FBG impulse response using low-coherence interferometry, and then we calculate the refractive index profile using layer peeling. This yields the complex longitudinal refractive index profile, which includes both the index modulation amplitude and the effective index as a function of position along the FBG. We demonstrate how this measurement can be applied to the calibration of a scanning-beam dithered phase mask FBG writing system. We demonstrate the ability to identify errors in the writing process that would not likely be found from a measurement of the FBG reflection spectrum alone     

Extension of measurement bandwidth in an AMB-based gyroscopic sensor

A gyroscopic sensor using active magnetic bearing (AMB) is studied both theoretically and experimentally. The sensor has been proposed to realize high accuracy, compact and low-cost sensors, and it utilizes the control function of the AMB. The sensor works as a two-axis gyroscopic sensor and also as a three-axis servo-type accelerometer. Angular velocities and accelerations are measured based on the control signals for cancelling the inertial effects that act on the AMB rotor. The methods to detect the accelerations and angular velocities have been validated from several experimental results. In addition, it has been indicated that there is an upper limit in the measurement bandwidth of the sensor when the two-axis angular velocity is measured simultaneously. However, factors determining the limit have not been presented in a concrete manner. This paper discusses these factors and presents a methodology that can extend the measurement bandwidth of the sensor. The limiting factors are investigated extensively by analysis, numerical simulations and experiments with the AMB. The relationship between the measurement bandwidth and the control system is also investigated. In addition, the measurement range of the gyro is discussed.