双臂式空间机械臂捕捉目标问题

基于动量守恒关系,分析了空间机械臂抓取目标过程中的碰撞问题.针对单臂式系统提出了直臂抓取与广义直臂抓取构型,并将后者推广到双臂式空间机械臂系统.利用广义直臂抓取方法得到的空间机械臂构型,可有效减少碰撞作用对于空间机械臂系统角冲量、基座姿态的影响,保证了系统的稳定性,克服了控制算法中存在的构件转角和执行机构力矩限制问题.仿真证明了方法的有效性。

轮式移动仿人机器人的动力学建模与分析

利用高效迭代牛顿-欧拉方法对一个21自由度的轮式移动仿人机器人进行了整体动力学建模,该模型虽然维数较高,但消除了分块建模中需要对模块之间相互作用力进行建模的难点问题,并且由于机器人双臂的对称结构,当合理规划双臂运动时,动力学模型将得到部分简化。本文还对某关节运动时在各个关节所产生的力或力矩进行了仿真分析。解析及仿真结果表明,合理规划上臂各关节的协调运动,将极大地削弱车体及腰部各关节所受的力或力矩扰动,为基于动力学的机器人运动控制以及稳定性分析提供理论依据。

新型蛇形机器人蜿蜒运动的动力学分析

为提高蛇形机器人执行各种运动的能力,研制了新型蛇形机器人系统.重点研究了该蛇形机器人的动力学.建立了机器人的运动学模型,并根据运动学模型提出了控制蛇形机器人蜿蜒运动的复合运动控制方法.用拉格朗日方法建立动力学模型,对不同参数下蛇形机器人的关节力矩特性和摩擦力特性进行了分析比较,为蛇形机器人的有效运动提供了理论依据.

蛇形机器人行波运动的研究

对蛇形机器人的行波运动机理进行了研究,基于Serpenoid曲线建立了蛇形机器人行波运动的形状控制模型、运动学模型、机构动力学模型及环境动力学模型,给出了求解过程。仿真结果表明:在行波运动中,各关节输入力矩大小呈周期变化,且随其与蛇体重心距离的增加而减小。蛇体中心关节的最大输入力矩为蛇形机器人所需最大输入力矩。对称关节输入力矩幅值变化规律相同,但相差不同;运动初始弯角保持不变,关节输入力矩随着环境摩擦因数的增加而增加。环境摩擦因数保持不变,关节输入力矩随着初始弯角的增加而减小。

基于加速度传感器反馈控制的谐波驱动系统的研究

在机器人驱动中经常采用谐波传动。但谐波减速器的柔性、非线性摩擦、随速度波动、低阻尼等因素会给负载端带来振动 ,导致工作端的轨迹跟踪精度不高。为了抑制其振动 ,实现高精度轨迹跟踪控制 ,提出利用加速度传感器反馈控制来抑制负载端的振动、力矩干扰和动力学效应 ,提高其响应性能。理论分析和实验结果证实了提出方法的可行性。

直接驱动机器人关节加速度反馈解耦控制

以利用线加速度传感器实际测量转动关节的加速度为基础 ,分析了机器人关节加速度反馈控制的开环模型 ,以及影响其闭环稳定性的主要因素 ;提出了闭环控制策略的设计准则 .在一台三自由度直接驱动机器人上的实验结果证明了该文分析的正确性 ,与不具备加速度反馈控制时的实验结果相比较 ,显示出这种方法的有效性

基于动力学约束的机械臂最优关节轨迹规划

本文提出了基于机械臂关节驱动力矩约束方程规划其关节最优运动轨迹的一种有效方法.该方法运用矩阵范数理论简化机械臂的动力学约束方程;在机械臂的关节空间内采用归一化的无因次量运用非线性规划法优化其运动轨迹.将所规划的无因次量轨迹方程作为机械臂产生实际运动轨迹的发生器,通过给定机械臂各运动段的起始和终止关节坐标,由系统的动力学约束方程计算出整个运动段所允许的最短运行时间,即生成所期望的运动轨迹.本文的轨迹规划方法计算效率高,可用于在线轨迹规划,文中通过算例证实了该方法的实用性.

The Effect of Transmission Design on Force-Controlled Manipulator Performance

Previous research in force control has focused on the choice of appropriate servo implementation without corresponding regard to the choice of mechanical hardware. This report analyzes the effect of mechanical properties such as contact compliance, actuator-to-joint compliance, torque ripple, and highly nonlinear dry friction in the transmission mechanisms of a manipulator. A set of requisites for high performance then guides the development of mechanical-design and servo strategies for improved performance. A single-degree-of-freedom transmission testbed was constructed that confirms the predicted effect of Coulomb friction on robustness; design and construction of a cable-driven, four-degree-of- freedom, "whole-arm" manipulator illustrates the recommended design strategies.

Cross-Border Unitization and Joint Development Agreements: An International Law Perspective

Okoye, Adaeze, et al, 'Cross-Border Unitization and Joint Development Agreements: An International Law Perspective', Houston Journal of International Law (2007) 29(2) pp.355-425 RAE2008

Effect of solder volume on joint shape with variable chip-to-board contact pad ratio

The objective of this paper is to investigate the effect of the pad size ratio between the chip and board end of a solder joint on the shape of that solder joint in combination with the solder volume available. The shape of the solder joint is correlated to its reliability and thus of importance. For low density chip bond pad applications Flip Chip (FC) manufacturing costs can be kept down by using larger size board pads suitable for solder application. By using “Surface Evolver” software package the solder joint shapes associated with different size/shape solder preforms and chip/board pad ratios are predicted. In this case a so called Flip-Chip Over Hole (FCOH) assembly format has been used. Assembly trials involved the deposition of lead-free 99.3Sn0.7Cu solder on the board side, followed by reflow, an underfill process and back die encapsulation. During the assembly work pad off-sets occurred that have been taken into account for the Surface Evolver solder joint shape prediction and accurately matched the real assembly. Overall, good correlation was found between the simulated solder joint shape and the actual fabricated solder joint shapes. Solder preforms were found to exhibit better control over the solder volume. Reflow simulation of commercially available solder preform volumes suggests that for a fixed stand-off height and chip-board pad ratio, the solder volume value and the surface tension determines the shape of the joint.

Quality control autophagy: a joint effort of ubiquitin, protein deacetylase and actin cytoskeleton.

Autophagy has been predominantly studied as a nonselective self-digestion process that recycles macromolecules and produces energy in response to starvation. However, autophagy independent of nutrient status has long been known to exist. Recent evidence suggests that this form of autophagy enforces intracellular quality control by selectively disposing of aberrant protein aggregates and damaged organelles--common denominators in various forms of neurodegenerative diseases. By definition, this form of autophagy, termed quality-control (QC) autophagy, must be different from nutrient-regulated autophagy in substrate selectivity, regulation and function. We have recently identified the ubiquitin-binding deacetylase, HDAC6, as a key component that establishes QC. HDAC6 is not required for autophagy activation per se; rather, it is recruited to ubiquitinated autophagic substrates where it stimulates autophagosome-lysosome fusion by promoting F-actin remodeling in a cortactin-dependent manner. Remarkably, HDAC6 and cortactin are dispensable for starvation-induced autophagy. These findings reveal that autophagosomes associated with QC are molecularly and biochemically distinct from those associated with starvation autophagy, thereby providing a new molecular framework to understand the emerging complexity of autophagy and therapeutic potential of this unique machinery.

Patient expectation is the most important predictor of discharge destination after primary total joint arthroplasty.

The purpose of this study was to identify preoperative predictors of discharge destination after total joint arthroplasty. A retrospective study of three hundred and seventy-two consecutive patients who underwent primary total hip and knee arthroplasty was performed. The mean length of stay was 2.9 days and 29.0% of patients were discharged to extended care facilities. Age, caregiver support at home, and patient expectation of discharge destination were the only significant multivariable predictors regardless of the type of surgery (total knee versus total hip arthroplasty). Among those variables, patient expectation was the most important predictor (P < 0.001; OR 169.53). The study was adequately powered to analyze the variables in the multivariable logistic regression model, which had a high concordance index of 0.969.

Unipedal balance is affected by lower extremity joint arthroplasty procedure 1 year following surgery.

Lower Extremity Joint Arthroplasty (LEJA) surgery is an effective way to alleviate painful osteoarthritis. Unfortunately, these surgeries do not normalize the loading asymmetry during the single leg stance phase of gait. Therefore, we examined single leg balance in 234 TJA patients (75 hips, 65 knees, 94 ankles) approximately 12 months following surgery. Patients passed if they maintained single leg balance for 10s with their eyes open. Patients one year following total hip arthroplasty (THA-63%) and total knee arthroplasty (TKA-69%) had similar pass rates compared to a total ankle arthroplasty (TAA-9%). Patients following THA and TKA exhibit better unilateral balance in comparison with TAA patients. It may be beneficial to include a rigorous proprioception and balance training program in TAA patients to optimize functional outcomes.

Percent body fat more associated with perioperative risks after total joint arthroplasty than body mass index

Copyright © 2014 Elsevier Inc. All rights reserved.Understanding the impact of obesity on elective total joint arthroplasty (TJA) remains critical. Perioperative outcomes were reviewed in 316 patients undergoing primary TJA. Higher percent body fat (PBF) was associated with postoperative blood transfusion, increased hospital length of stay (LOS) >3 days, and discharge to an extended care facility while no significant differences existed for BMI. Additionally, PBF of 43.5 was associated with a 2.4× greater likelihood of blood transfusion, PBF of 36.5 with a 1.9× greater likelihood for LOS >3 days, and PBF of 36.0 with a 1.4× greater likelihood for discharge to an extended care facility. PBF may be a more effective measure than BMI to use in screening for perioperative risks and acute outcomes associated with obese total joint patients.