用块稀疏贝叶斯学习算法重构识别体域网步态模式

针对低功耗体域网步态远程监测终端非稀疏加速度数据重构和步态模式识别性能优化问题,提出了一种基于块稀疏贝叶斯学习的体域网远程步态模式重构识别新方法,该方法基于体域网远程步态监测系统架构和压缩感知框架,在体域网传感节点利用线性稀疏矩阵压缩原始加速度数据,减少传输数据量,降低其功耗,同时在远程终端基于块稀疏贝叶斯学习算法充分利用加速度数据块结构内在相关性,获取加速度数据内在稀疏性,有效提高非稀疏加速度数据重构性能,为准确识别步态模式提供可靠的数据支撑.采用USC-HAD数据库中行走、跑、跳、上楼、下楼五种步态运动的加速度数据验证新方法的有效性,实验结果表明,基于所提算法的加速度数据重构性能明显优于传统压缩感知重构算法性能,使基于支持向量机多步态分类器识别准确率可达98%,显著提高体域网远程步态模式识别性能.所提新方法不仅有效提高非稀疏加速度数据重构和步态模式识别性能,并且也有助于设计低功耗、低成本的体域网加速度数据采集系统,为体域网远程监测步态模式变化提供一个新方法和新思路.     

Effects of milking on dairy cow gait

We studied cows with (n = 6) and without (n = 26) sole ulcers before and after milking to explore how milking influences dairy cattle gait and how this differs for cows with hoof injuries. Video recordings of cows were digitized using motion-analysis software to calculate stride variables for each hoof. Gait was scored using a 1-to-5 numerical rating system (1 = sound, 5 = severely lame) and a continuous 100-unit visual analog scale of gait attributes (back arch, head bob, tracking-up, and reluctance to bear weight). For cows with and without sole ulcers, differences in gait before and after milking were evident; after milking, all cows had significantly longer strides (123.3 vs. 133.5 ± 2.0 cm, respectively), higher stride height (8.3 vs. 8.9 ± 0.1 cm), shorter stride durations (1.49 vs. 1.41 ± 0.03 s), walked faster (0.85 vs. 0.97 ± 0.03 m/s), and had shorter periods of triple support (3 legs in ground contact; 80.0 vs. 71.7 ± 2.0%). Tracking-up and reluctance to bear weight improved after milking (20 vs. 16 ± 2; 20 vs. 15 ± 1, respectively), but numerical rating scores and back arch did not. Cows with sole ulcers walked differently than cows without for all measures, except swing duration, both before and after milking. Interactions between hoof health and milking were found for swing duration and head bob but when tested separately, the only effect was that cows without sole ulcers had longer swing durations before milking (0.45 vs. 0.44 ± 0.01 s, respectively). Gait differences were probably due to udder distention and motivation to return to the home pen. Our results suggest that the most suitable time to assess lameness is after milking when differences between cows with and without ulcers are most evident.     

Comparison of models to identify lame cows based on gait and lesion scores, and limb movement variables

Bovine lameness results in pain and suffering in cattle and economic loss for producers. A system for automatically detecting lame cows was developed recently that measures vertical force components attributable to individual limbs. These measurements can be used to calculate a number of limb movement variables. The objective of this investigation was to explore whether gait scores, lesion scores, or combined gait and lesion scores were more effectively captured by a set of 5 limb movement variables. A set of 700 hind limb examinations was used to create gait-based, lesion-based, and combined (gait- and lesion-based) models. Logistic regression models were constructed using 1, 2, or 3 d of measurements. Resulting models were tested on cows not used in modeling. The accuracy of lesion-score models was superior to that of gait-score models; lesion-based models generated greater values of areas under the receiving operating characteristic curves (range 0.75 to 0.84) and lower mean-squared errors (0.13 to 0.16) compared with corresponding values for the gait-based models (0.63 to 0.73 and 0.26 to 0.31 for receiving operating characteristic and mean-squared errors, respectively). These results indicate that further model development and investigation could generate automated and objective methods of lameness detection in dairy cattle.     

线性插值框架下矩阵步态识别的性能分析

针对现有的步态周期检测方法检测效果不佳以及行走速度变化对步态识别性能有很大影响的问题,提出的基于矩的步态周期检测方法中,Zernike矩需要人体居中、尺度归一的前期预处理过程,而伪Zernike矩具有能描述运动图像的特点,它可以避免人体居中、尺度归一等处理,以便直接测试步态的周期性.根据行走时的两帧之间的特征取决于前一帧和后一帧的特征,提出了基于线性插值的矩阵步态识别算法框架,并且将投影特征、Hough变换特征、Trace变换特征和Fan-Beam映射特征应用在CASIA(B)步态库上,验证了框架的有效性,为解决步态识别问题带来新的方法与思路.这种基于线性插值的矩阵步态识别特征本质上是一种权值不同的能量形式.     

Locomotion characteristics of dairy cows walking on pasture and the effect of artificial flooring systems on locomotion comfort

The locomotion comfort of dairy cows depends on the floor of the walking alleys. Optimal locomotion comfort is given when cows walk on pasture, allowing freedom from discomfort and pain and the expression of normal behavior. This study examined the characteristics of locomotion behavior on pasture (gold standard with optimal locomotion comfort) and compared it with behaviors of cows walking on mastic asphalt or solid rubber mats before and after a routine claw trimming session. Our hypotheses were (1) that gait variables were different on pasture versus mastic asphalt and on mastic asphalt versus rubber, and (2) that claw trimming had an effect on gait variables of cows walking on mastic asphalt. Twenty-four dairy cows kept in a tiestall facility were enrolled in this experimental trial. The pedogram was measured using 2 standalone 3-dimensional accelerometers (400 Hz), attached to the metatarsus of both hind limbs. The extracted pedogram variables included temporal events (kinematic outcome = gait cycle and stance-phase and swing-phase durations) and peaks (kinetic outcome = foot load, toe-off). The cows were further video-recorded to calculate walking speed and stride length. Locomotion score was performed on mastic asphalt to enroll only nonlame cows (locomotion score <3). For comparison between different floor types, repeated-measures ANOVA was performed with the cow as a subject variable, session time of measurement as within-subject variable, and flooring type as a fixed effect. Three separate analyses were performed: pasture versus mastic asphalt (analysis I), solid rubber versus mastic asphalt (analysis II), and the effect of claw trimming on the kinematic and kinetic variables on mastic asphalt (analysis III). All tested gait variables were significantly different between pasture and mastic asphalt floor. The optimal characteristics of locomotion comfort on pasture included shorter duration of gait cycle, longer stance-phase duration, shorter swing-phase duration, higher walking speed, longer stride length, and higher peaks of foot load and toe-off. However, gait variables of cows walking on rubber mats did not show any significant difference compared with the mastic asphalt floor; only stride length tended to be longer on rubber mats. In addition, the stance- and swing-phase durations significantly improved shortly after trimming. The left–right differences of the stance- and swing-phase durations tended to decrease after claw trimming when cows walked on asphalt floor. The results of this study show that solid rubber flooring does not result in significant improvement of the evaluated variables of locomotion comfort compared with mastic asphalt.     

足踝步态模拟机运动学和动力学分析

研究足踝步态模拟机运动学和动力学,为试验台运动驱动提供理论依据,验证试验台的仿真能力。设计了一种五自由度的步态模拟机,建立了Adams虚拟样机和足踝模型,并对其进行运动学和动力学仿真,与活体实验数据比对了足踝运动特性曲线、胫骨轴在矢状面的旋转特性曲线及着地相进程中的足底反力。根据仿真中控制规律,对实验台进行了运动学和动力学验证。结果表明,模拟机的踝关节位移模拟结果曲线与活体实验测量结果曲线吻合良好,最大误差低于5%;同时能够较精确模拟人体胫骨轴旋转运动趋势;足底反力与活体测量数据较为吻合;试验台重复良好特性。     

一种仿真数字人步态规划优化算法

为了研究下肢骨骼服的行走步态.构造了HL-1(华理1号)仿真数字人体模型,并对数字人进行了步态规划.为了确保数字人行走的稳定,避免数字人行走过程中关节驱动的冲击,减小脚与地面的碰撞,在考虑前向与侧向运动存在耦合的条件下,提出了将正运动学和逆运动学方法相结合的步态规划优化算法,克服了原有的数字人步态求解方法的不足.应用该算法求得步态周期函数,仿真数字人在Matlab和Adams环境下进行了协同仿真,实现了数字人的平稳行走,验证了该步态规划优化算法的可行性.     

Effects of obstacle height on the control of the body center of mass motion during obstructed gait

Abstract

Tripping over obstacles has been reported as one of the most frequent causes of falls in the elderly. Since a successful crossing requires the stability of the body through the control of the motion of the body center of mass (COM), the purpose of this study was to investigate the COM motion when crossing obstacles of different heights. Ten young healthy adults walked and crossed obstacles of heights of 10%, 20% and 30% of their leg lengths in a gait laboratory. The COM motions were calculated using data measured from a motion analysis system. It was found that vertical motions of the COM, including position, velocity and acceleration, were all modulated to successfully cross obstacles of different height. All acceleration components of the COM were changed with increased obstacle height, suggesting that different forces from muscle contractions were needed to control COM stability when facing different obstacle heights. These findings may help shed light on further investigation of the motor control strategies of the central nervous system for obstacle crossing and serve as baseline data in the evaluation of the elderly and patients.     

Can a new ergonomical ankle–foot orthosis (AFO) device improve patients’ daily life? A preliminary study

Abstract

Approximately two-thirds of patients survive following a cerebral vascular accident (stroke), nevertheless about half are left with a physical incapacity. The clinical picture is frequently a combination of motor, sensory, visual and cognitive deficits. Mechanically, the use of ankle-foot orthosis (AFO) appear a good option. The objective of this study was to quantify the impact of the AFO on patients having a deficit of dorsi-flexion during gait in the aim to improve their daily lives. Different biomechanical variables were analysed such as parameters of Balance in static position and spatio-temporal (ST) ones in dynamics. Seven patients were enrolled in this study (53.57 ± 16.17 years old, 1.80 ± 0.07 m height and 89 ± 15.06 kg body mass). The pressure force plate used in this experimentation aimed to measure the patients’ behaviors with and without AFO. The results showed a significant impact of AFO in terms of ST analysis (p < 0.05). These results can be related to the fact that the orthosis supports the foot during walking and propels the step during the initial swing phase. In posturography, the results showed that patients increased their balance by using AFO (p < 0.05). This result permits the patients a better expansion of their movements during gait after an immediate benefit.