基于抓持分类的接触力分解

研究了机器人手抓持物体时接触力、物体所受外力以及手指关节力矩之间的关系。文中针对三类抓持，分别给出了接触力分解的一般表达式，这些表达式比以往文献更有特点     

多指灵巧手基于广义力椭球的最优抓持规划

首先在抓持系统的力旋量空间中 ,建立了关节力矩与物体外力的关系 ,定义了整个手物体抓持系统的雅可比矩阵。按照关节空间和物体空间的力的映射关系 ,提出了广义力椭球和内力椭球。在此基础上 ,定义了抓持系统的最优抓持能力和最优内力。最后 ,按抓持能力和最优内力对多指灵巧手进行最优抓持规划     

双臂机器人抓持工件的力分解

针对双臂机器人抓持工件的协调运动 ,研究了抓持力的分解 ,基于最小范数和最小关节广义驱动力得到了力分解的两种方案 ,算例的仿真计算验证了方案的可行性。     

仿人四指灵巧手的抓持能力分析

对四指仿人灵巧手的结构及单手指运动学及动力学进行了分析,为深入地研究该灵巧手的控制提供了理论依据。在ADAMS中进行了灵巧手抓取物体仿真实验,实时得到手指与抓取物体间的接触力值。并利用有限元方法分析了灵巧手在强力抓取时的手指结构的力学性能,验证了该灵巧手可以达到实现设计目标所要求的抓取载荷。为抓取实验提供了抓取物体重量的理论分析依据。     

自适应抓持仿人手的抓持能力分析

以三自由度的仿人手为研究对象,对其抓持物体的能力进行研究。在对仿人手抓持给定形状和大小物体的受力进行分析的基础上,给出了以抓持起最重物体为目标函数的优化分析计算模型,得到了仿人手在具有最大抓持能力时手指各指节与物体之间的作用力的大小。最后获取了“解耦装置”中弹簧预紧力的计算方法,并根据优化所得到的各力值计算得到了该预紧力的大小。     

一种自适应拟人手指抓持力分析与结构优化

采用齿轮齿条传动机构,设计了一种新型自适应拟人手指。该手指自身不带驱动器,适合抓取不同形状、尺寸的物体,使机器人多指手以较少的驱动器驱动较多关节自由度。电机的数量大大减少使机器人手具有许多优点。另外,该手指与人的手指相似,适合用于拟人多指手。分析了该手指抓持力与其设计参数的关系,提出了该手指的结构优化设计原则。     

基于抓持矩阵的二指多关节手抓持规划和丝传动设计

二指手的欠驱动手指,能够模仿人的拇指和中指,实现对不同物体的抓持并完成抓放的任务。针对一般物体,利用丝传动的欠驱动手能更好地模仿人的手指,从而实现两个手指对于物体的抓持,并完成抓放任务。利用抓持矩阵的方法,建立二指多关节手对物体有摩擦接触的抓持模型,并将抓持矩阵逐步向外扩展到手指的各个关节处,进而建立扩展抓持矩阵。利用接触点处抓持矩阵确定了一类平面物体抓持规划中接触点的位置应该满足的条件,并在最小力的原则下计算物体在不同的位姿下抓持力的大小。利用上述规划的接触点进行运动学反解,进而从联动关节处的抓持矩阵提取出欠驱动手指两个耦合关节力矩信息,得出丝传动的半径设计和反向弹簧设计的原则。利用扩展抓持矩阵求得力矩分量并用之验证此法与常规求法求得的力矩是等效的,从而验证此方法的正确性并对丝传动进行位置与力的计算。     

无系留大负载软体抓持机器人研究发展综述

受软体材料、制造工艺、核心部件的限制,大多数的软体机器人负载能力较低,不能随机携带控制和能量硬件系统,不得不通过管路和线路系留在外部硬件上,这严重限制了软体机器人的作业范围和应用领域.在众多的软体机器人中,软体抓持机器人发展较快,主要包括两类:一类是软体末端,主要配合机械臂、水下机器人、无人机、人体等完成抓取任务;另一...     

基于方向可操作度的机器人灵巧手抓持优化研究

以三指灵巧手的速度可操作性椭球和力可操作性椭球研究为基础,定义了机构的速度方向可操作度和力方向可操作度。在给定灵巧手操作位姿的条件下,以方向可操作度为目标函数,给出了灵巧手最佳传速方向和传力方向的优化方法。最后,以三指灵巧手为算例进行演示,得出了灵巧手在给定位姿下的最佳传速方向和传力方向,为灵巧手的抓持规划提供了值得借鉴的方法。     

三指灵巧手结构设计及接触力规划

针对传统灵巧手追求灵活性而带来其外形尺寸过大、结构复杂的问题,设计一种小巧紧凑而灵活性高的全驱动三指灵巧手并建立其三维模型。采用拉格朗日法建立单手指动力学模型并进行动力学分析。然后将灵巧手三维模型导入ADAMS软件中建立灵巧手虚拟样机进行仿真,得到其运动学与动力学等性能曲线。利用MATLAB软件对其动力学方程进行数值分析,其理论分析结果与ADAMS仿真结果一致,验证了理论计算的正确性和灵巧手结构设计的合理性。基于拉格朗日乘子法求取抓取力初值,通过引入稳定系数对其进行优化得到优化接触力,同时也验证了其在手指关节驱动力矩约束下的合理性,为灵巧手手指抓取力计算提供了新的参考。     

FORCE OPTIMIZATION OF GRASPING BY ROBOTIC HANDS

It is important for robotic hands to obtain optimal grasping performance in the meanwhile balancing external forces and maintaining grasp stability. The problem offeree optimization of grasping is solved in the space of joint torques. A measure of grasping performance is presented to protect joint actuators from working in heavy payloads. The joint torques are calculated for the optimal performance under the frictional constraints and the physical limits of motor outputs. By formulating the grasping forces into the explicit function of joint torques, the frictional constraints imposed on the grasping forces are transformed into the constraints on joint torques. Without further simplification, the nonlinear frictional constraints can be simply handled in the process of optimization. Two numerical examples demonstrate the simplicity and effectiveness of the approach.     

PREDICTION OF CUTTING FORCES IN MACHINING WITH RESTRICTED CONTACT TOOLS

Abstract

A semi-empirical method is described for predicting cutting forces in orthogonal machining with restricted contact tools. The method uses a well-established machining theory to predict cutting forces and tool-chip contact length for the corresponding plane face tool, i.e., a tool having the same cutting-edge geometry but no restricted contact. These predicted parameters and a set of empirical relations are then used to calculate the cutting forces for the restricted contact tool. A comparison between predicted and experimental results for two plain carbon steel work materials and a range of tool geometries and cutting conditions shows good agreement.     

EXPERIMENTAL INVESTIGATIONS OF THE FORCE DISTRIBUTIONS IN THE GRINDING CONTACT ZONE

This paper is concerned with the experimental investigations for the prediction of the grinding force distribution in the grinding wheel and workpiece contact zone. A new approach was developed to predict the force distribution using the horizontal and vertical forces measured while grinding a workpiece with a shorter length along the grinding pass. Straight surface grinding experiments were conducted using straight oil as grinding fluid on a nickel-based alloy (IN718) with a 60-grit 150 mm diameter electroplated CBN wheel to implement this approach and to investigate the effects of wheel speeds and workspeeds on the distributions. Grinding power and forces were measured. It was found that the distribution along contact arc increases with a decreasing rate from bottom to top. Wheel speeds have a significant effect on the normal force distribution at the higher removal rate. The grinding power was estimated to verify the predicted force distribution and it was found to be in a good agreement with the measured power.     

EFFECT OF FRICTIONAL FORCE ON GEARING CONTACT FATIGUE STRENGTH

The model for computing frictional coefficient between two teeth faces at the state of mixed elastohydrodynamic lubrication is established. And then more than 80 sets of numerical calculations and six sets of disc fatigue tests are completed. The results show that when the film thickness ratio λ＜1.6, frictional coefficient μ is drastically decreased as λ rises; Thereafter it decreases smoothly until λ=4.5. When λ＞4.5, however, it goes up again with λ, which indicates that the excessive film thickness ratio will deteriorate gearing contact fatigue strength. At the end, the formulae for determining the frictional coefficients are formed.     

齿面摩擦力对齿轮接触应力的影响

渐开线齿轮接触疲劳强度设计中忽略了齿面摩擦力的影响。对此 ,众多学者看法不一 ,有的认为齿面摩擦力影响甚微 ,可以忽略 ;而另一些人则指出其影响明显 ,不可不计。文中通过 6组滚子疲劳试验得出 ,齿面摩擦力的影响能否被忽略与齿轮的转速、功率、材质、齿数、模数及润滑剂的黏度等因素有关 ,而这些因素可用一个无量纲参数S来表示。S存在两个临界点S1 和S2 。当S S2 时 ,摩擦力影响较小 ,可以忽略不计 ;当S1 相似文献   

预测含间隙机构副元素分离和碰撞的力判定方法

通过解析分析，对预测含间隙平面连杆机构运动副元素分离的方法进行了改进，指出了原方法的不足之处。改进后的预测方法的精确性和稳定性都大为提高，使得对平面连杆机构运动副元素分离的预测更准确有效。     

VELOCITY ANALYSIS OF A SPATIALM ECHANISM USING THE PRINCIPLEOF VIRTUAL FORCES

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THEORETICAL PREDICTION OF TOOL-CHIP CONTACT LENGTH IN ORTHOGONAL METAL MACHINING BY COMPUTER SIMULATION

A method for determination of tool-chip contact length is theoretically presented in orthogonal metal machining. By using computer simulation and based on the analyses of the elastro-plastic deformation with lagrangian finite element method in the deformation zone, the accumulated representative length of the low layer, the tool-chip contact length of the chip contacting the tool rake are calculated, experimental studies are also carried out with 0.2% carbon steel. It is shown that the tool-chip contact lengths obtained from computer simulation have a good agreement with those of measured values.     

CUTTING DISTURBANCES INFLUENCED BY VARIATIONS IN CONTACT SURFACE GEOMETRY

The significant cutting disturbances appearing in hard turning processes cause shifting of the process dynamics. Therefore, in this paper the turning process is evaluated by radial force variation analysis, as a function of depth of cut, tool nose radius and effective lead edge angle, through static and dynamic indicators. The tool/workpiece contact zone is, in the case of hard turning, mostly limited within the tool nose radius region. Therefore in this paper, geometry of the tool/workpiece contact line is analyzed. The depth of cut is calculated as a geometric difference of prior and instantaneous tool pass profiles. The calculated values of the depth of cut are time dependant, and can vary by 60%. Various process monitoring techniques have been used to identify and confirm these variations, as well as quantify the level of process stability. The results obtained confirm the assumption that effective lead edge angle and radial force are influenced by depth of cut, feed rate and tool nose radius. Additionally, it is shown that low values of depth of cut and geometry of prior pass-machined surface valleys shift the hard turning process to a dynamically more sensitive level as compared the case of soft machining.