In the realm of quadruped robot locomotion,compliance control is imperative to handle impacts when negotiating unstructured terrains.At the same time,kinematic tracking accuracy should be guaranteed during locomotion....In the realm of quadruped robot locomotion,compliance control is imperative to handle impacts when negotiating unstructured terrains.At the same time,kinematic tracking accuracy should be guaranteed during locomotion.To meet both demands,ajoint space compliance controller is designed,so that compliance can be achieved in stance phase while position tracking performance can be guaranteed in swing phase.Unlike operational space compliance control,the joint space compliance control method is easy to implement and does not depend on robot dynamics.As for each joint actuator,high performance force control is of great importance for compliance design.Therefore,a nonlinear PI controller based on feedback linearization is proposed for the hydraulic actuator force control.Besides,an outer position loop（compliance loop）is closed for each joint.Experiments are carried out to verify the force controller and compliance of the hydraulic actuator.The robot leg compliance is assessed by a virtual prototyping simulation.展开更多
Assessing the radiographic features of knee osteoarthritis （OA）, especially joint space narrowing, is important for evaluating disease progression. The purpose of this study was to quantitatively analyze joint space...Assessing the radiographic features of knee osteoarthritis （OA）, especially joint space narrowing, is important for evaluating disease progression. The purpose of this study was to quantitatively analyze joint space narrowing by measuring 2 new variables： the average joint space width （aJSW） and the articulate angle （AA） on X-ray films, and to evaluate the relationship between the 2 variables, knee function and OA symptoms. Methods Using the web-based radiology viewer （Cedara I-ReachTM 4.1.1）, we measured the 2 variables in 50 knees of 41 patients with knee OA participating in the Shanghai OA Study. We also evaluated the Kellgren-Lawrence （K-L） grade, the Western Ontario and McMaster Universities OA Index （WOMAC）, and additional questionnaire in OA knees. The study was approved by the ethics committee of Shanghai Ninth People＇s Hospital （No. 2009-28）. Results The aJSW correlated with the K-L grade （r=-0.57, P 〈0.001）, kneeling （r=-0.29, P=0.04）, sitting cross-legged on the floor （r=-0.31, P=0.03）, WOMAC pain （r=-0.31, P=0.03）, WOMAC disability （r=-0.35, P=0.01）, pain while squatting （r=-0.37, P=0.01）, and defecating in a squatting position （r=-0.39, P= 0.01）. The AA correlated with defecating in a squatting position （r=0.29, P=0.05）, WOMAC disability （r=0.30, P=0.04） and K-L grade （r=0.44, P=0.003）. The K-L grade also correlated with pain while squatting （r=-0.40, P=0.005） and defecating in a squatting position （r=-0.34, P=0.02）, WOMAC pain （r=0.30, P=0.04）, and WOMAC disability （r=0.30, P=0.04）. Conclusions The aJSW closely correlated with knee OA symptoms and function scores, and was more sensitive to knee OA related disabilities than K-L grade and the AA. The aJSW could be used as a new variable for knee OA evaluation.展开更多
This letter addresses the recent study by Zhu et al on the predictive factors for coronal and sagittal graft extrusion length following medial meniscus reconstruction using tendon autografts.The study provides valuabl...This letter addresses the recent study by Zhu et al on the predictive factors for coronal and sagittal graft extrusion length following medial meniscus reconstruction using tendon autografts.The study provides valuable insights into the importance of preoperative joint space width and tunnel positioning as predictors of graft extrusion.Specifically,it found strong correlations between preoperative joint space width and medial,posterior,and mean graft extrusion at both 1 week and 8 months post-operation.Additionally,tunnel edge distance at 1 week postoperation correlated with anterior and posterior graft extrusion.These findings offer critical guidance for improving surgical outcomes.However,the letter highlights the need for further research with larger sample sizes and comparative studies involving different graft types to strengthen these findings and broaden their applicability in clinical settings.The study's contributions to understanding meniscus reconstruction using tendon autografts are acknowledged,along with suggestions for future research directions.展开更多
当干扰信号的空域和极化域特征与目标信号相似时,采用空极化域联合抗干扰技术在消除干扰的同时也会抑制目标信号,导致干扰对消后信干噪比(signal to interference plus noise ratio,SINR)低于雷达系统需求,从而形成干扰对消盲区。针对...当干扰信号的空域和极化域特征与目标信号相似时,采用空极化域联合抗干扰技术在消除干扰的同时也会抑制目标信号,导致干扰对消后信干噪比(signal to interference plus noise ratio,SINR)低于雷达系统需求,从而形成干扰对消盲区。针对这一现象,通过在空域、极化域与空极化域分别建立交替极化阵列对消盲区模型,推导了对消盲区位置和大小的数学表达式,从而给出了交替极化阵列对消盲区的数学表征方法。进而分析了交替极化阵列对消盲区的分布规律与影响因素,研究发现阵元间距能够显著影响交替极化阵列对消盲区的分布,在相同条件下交替极化阵列对消盲区大于共点极化阵列对消盲区,结果表明交替极化阵列虽然通过减少天线数目降低了设备成本,但增大了阵列的对消盲区。然后,对消盲区模型进行了数值仿真,仿真结果验证了理论分析。最后,利用信道模拟器搭建了实验平台,信道模拟实验测得的对消盲区与理论值基本一致,再次证明了分析结论的有效性。展开更多
基金Supported by the National High Technology Research and Development Program of China(863 Program)(2011AA041002)
文摘In the realm of quadruped robot locomotion,compliance control is imperative to handle impacts when negotiating unstructured terrains.At the same time,kinematic tracking accuracy should be guaranteed during locomotion.To meet both demands,ajoint space compliance controller is designed,so that compliance can be achieved in stance phase while position tracking performance can be guaranteed in swing phase.Unlike operational space compliance control,the joint space compliance control method is easy to implement and does not depend on robot dynamics.As for each joint actuator,high performance force control is of great importance for compliance design.Therefore,a nonlinear PI controller based on feedback linearization is proposed for the hydraulic actuator force control.Besides,an outer position loop（compliance loop）is closed for each joint.Experiments are carried out to verify the force controller and compliance of the hydraulic actuator.The robot leg compliance is assessed by a virtual prototyping simulation.
文摘Assessing the radiographic features of knee osteoarthritis （OA）, especially joint space narrowing, is important for evaluating disease progression. The purpose of this study was to quantitatively analyze joint space narrowing by measuring 2 new variables： the average joint space width （aJSW） and the articulate angle （AA） on X-ray films, and to evaluate the relationship between the 2 variables, knee function and OA symptoms. Methods Using the web-based radiology viewer （Cedara I-ReachTM 4.1.1）, we measured the 2 variables in 50 knees of 41 patients with knee OA participating in the Shanghai OA Study. We also evaluated the Kellgren-Lawrence （K-L） grade, the Western Ontario and McMaster Universities OA Index （WOMAC）, and additional questionnaire in OA knees. The study was approved by the ethics committee of Shanghai Ninth People＇s Hospital （No. 2009-28）. Results The aJSW correlated with the K-L grade （r=-0.57, P 〈0.001）, kneeling （r=-0.29, P=0.04）, sitting cross-legged on the floor （r=-0.31, P=0.03）, WOMAC pain （r=-0.31, P=0.03）, WOMAC disability （r=-0.35, P=0.01）, pain while squatting （r=-0.37, P=0.01）, and defecating in a squatting position （r=-0.39, P= 0.01）. The AA correlated with defecating in a squatting position （r=0.29, P=0.05）, WOMAC disability （r=0.30, P=0.04） and K-L grade （r=0.44, P=0.003）. The K-L grade also correlated with pain while squatting （r=-0.40, P=0.005） and defecating in a squatting position （r=-0.34, P=0.02）, WOMAC pain （r=0.30, P=0.04）, and WOMAC disability （r=0.30, P=0.04）. Conclusions The aJSW closely correlated with knee OA symptoms and function scores, and was more sensitive to knee OA related disabilities than K-L grade and the AA. The aJSW could be used as a new variable for knee OA evaluation.
文摘目的 评价磁共振3D space序列在膝关节半月板放射状撕裂中的诊断价值,提高对此病的影像认识,为临床诊疗提供帮助。方法 回顾性分析29例经关节镜证实的膝关节半月板放射状撕裂患者的磁共振资料;对比常规磁共振2D序列与3D space序列在半月板放射状撕裂病变中的诊断效能,使用Fisher确切概率法对两种方法诊断半月板放射状撕裂的准确率进行比较。结果 3D space序列和常规2D序列诊断半月板放射状撕裂的准确率分别为96.7%(29/30)、80.0%(24/30),3D space序列诊断准确率高于常规2D序列,差异有统计学意义(P<0.05)。结论 3D space序列在半月板放射状撕裂的诊断中具有较高价值,其诊断效能优于2D序列。
文摘This letter addresses the recent study by Zhu et al on the predictive factors for coronal and sagittal graft extrusion length following medial meniscus reconstruction using tendon autografts.The study provides valuable insights into the importance of preoperative joint space width and tunnel positioning as predictors of graft extrusion.Specifically,it found strong correlations between preoperative joint space width and medial,posterior,and mean graft extrusion at both 1 week and 8 months post-operation.Additionally,tunnel edge distance at 1 week postoperation correlated with anterior and posterior graft extrusion.These findings offer critical guidance for improving surgical outcomes.However,the letter highlights the need for further research with larger sample sizes and comparative studies involving different graft types to strengthen these findings and broaden their applicability in clinical settings.The study's contributions to understanding meniscus reconstruction using tendon autografts are acknowledged,along with suggestions for future research directions.
文摘当干扰信号的空域和极化域特征与目标信号相似时,采用空极化域联合抗干扰技术在消除干扰的同时也会抑制目标信号,导致干扰对消后信干噪比(signal to interference plus noise ratio,SINR)低于雷达系统需求,从而形成干扰对消盲区。针对这一现象,通过在空域、极化域与空极化域分别建立交替极化阵列对消盲区模型,推导了对消盲区位置和大小的数学表达式,从而给出了交替极化阵列对消盲区的数学表征方法。进而分析了交替极化阵列对消盲区的分布规律与影响因素,研究发现阵元间距能够显著影响交替极化阵列对消盲区的分布,在相同条件下交替极化阵列对消盲区大于共点极化阵列对消盲区,结果表明交替极化阵列虽然通过减少天线数目降低了设备成本,但增大了阵列的对消盲区。然后,对消盲区模型进行了数值仿真,仿真结果验证了理论分析。最后,利用信道模拟器搭建了实验平台,信道模拟实验测得的对消盲区与理论值基本一致,再次证明了分析结论的有效性。
文摘针对车载雷达多参数联合超分辨计算复杂度高、无法快速实现参数估计的问题,提出了基于频域波束降维的多参数联合超分辨算法。所提算法通过快速傅里叶变换(fast Fourier transform,FFT)将空时多参数域联合数据变换到频域,处理感兴趣区域的多维频域数据,完成空时波束空间降维和基于频域数据的多参数联合超分辨,实现目标信息的快速联合估计。推导了频域子空间正交性及频域波束降维超分辨算法理论。仿真研究了算法的分辨率和估计性能与信噪比的关系。仿真结果表明,所提算法的精度和分辨率远超传统FFT算法,相对于传统多重信号分类(multiple signal classification,MUSIC)算法,所提算法计算量大幅降低。
