Design of a discrete bending joint using multiple unit PREF joints for isotropic 2-DOF motion

Miniature steerable robots are required for various medical applications. Although a typical continuum joint mechanism has a great advantage of miniaturization, it is difficult to have a small bending radius of curvature. With a discrete joint, it is easy to secure definite bending with strength; however, a coarsely structured joint cannot provide a stable distal rolling motion to the end-effector. This paper proposes a method to construct a 2-DOF discrete bending joint using multiple pulleyless rolling joints with an example of a 4-segmental joint. The effects of the stacking sequence on its performance are analyzed. Then, three evaluation criteria are established, and the best stacking sequences are determined. The proposed design method is valid for various numbers of unit joints, and it can be easily applied to the structural design of soft robots resembling snakes or elephant trunks.     

Static Force-Based Modeling and Parameter Estimation for a Deformable Link Composed of Passive Spherical Joints With Preload Forces

To balance the contradiction between higher flexibility and heavier load bearing capacity, we present a novel deformable manipulator which is composed of active rigid joints and deformable links. The deformable link is composed of passive spherical joints with preload forces between socket-ball surfaces. To estimate the load bearing capacity of a deformable link, we present a static force-based model of spherical joint with preload force and analyze the static force propagation in the deformable link. This yields an important result that the load bearing capacity of a spherical joint only depends on its radius, preload force, and static friction coefficient. We further develop a parameter estimation method to estimate the product of preload force and static friction coefficient. The experimental results validate our model. 80.4% of percentage errors on the maximum payload mass prediction are below 15%.      

焊点质量检测新方法

提出一种基于小波神经网络的焊点质量检测算法。首先对焊点图像进行预处理,然后提出采用形态因子和曲率作为焊点图像特征,最后建立焊点质量检测的小波神经网络模型。实验结果表明,提出的焊点质量检测算法具有较快的处理速度以及较高的准确率。     

基于UG的膨胀套管螺纹接头参数化建模

膨胀套管螺纹接头优化设计分析时需要反复修改接头参数,高效快速建立接头三维模型,本文提出了两种利用UG软件进行膨胀套管螺纹接头参数化建模的方法.在UG中完成接头模型样板后,第一种方法通过Visual Studio开发平台编写程序得到一个可改变结构参数的可执行程序,实现膨胀套管接头二次开发建模;另一种方法是基于PTS模块完...     

Topology optimization of frame structures with flexible joints

A method for structural topology optimization of frame structures with flexible joints is presented. A typical frame structure is a set of beams and joints assembled to carry an applied load. The problem considered in this paper is to find the stiffest frame for a given mass. By introducing design variables for beams and joints, a mass distribution for optimal structural stiffness can be found. Each beam can have several design variables connected to its cross section. One of these is an area-type design variable which is used to represent the global size of the beam. The other design variables are of length ratio type, controlling the cross section of the beam. Joints are flexible elements connecting the beams in the structure. Each joint has stiffness properties and a mass. A framework for modelling these stiffnesses is presented and design variables for joints are introduced. We prove a theorem which can be interpreted as the fact that the removal of structural elements, e.g. joints or beams, can be modelled by a small strictly positive material amount assigned to the element. This is needed for the computations of sensitivities used in the applied gradient based iterative method. Both two and three dimensional problems, as well as multiple load cases and multiple mass constraints, are treated.     

计算机辅助设计应用于斜轧健身器管孔型设计

健身器管材的宽高比等于3,并且要求焊缝在角部;长边与短边的连接圆角亦不相等,轧制难度较大。介绍了矩形健身器管焊缝在角部的斜轧轧制工艺及其孔型设计方法,在分析了轧制要求及难点的基础上,给出了孔型设计实施方案。应用计算机辅助孔型设计计算了不等圆角的斜轧矩形管各架次孔型尺寸,进行了孔型优化。将焊缝有效地控制在成型后矩形管的角部,保证了所生产的健身器管材的质量要求。     

Robust trajectory planning for robotic manipulators under payload uncertainties

A number of trajectory planning algorithms are available for determining the joint torques, positions, and velocities required to move a manipulator along a given geometric path in minimum time. These schemes require knowledge of the robot's dynamics, which in turn depend upon the characteristics of the payload which the robot is carrying. In practice, the dynamic properties of the payload will not be known exactly, so that the dynamics of the robot, and hence the required joint torques, must be calculated for a nominal set of payload characteristics. But since these trajectory planners generate nominal joint torques which are at the limits of the robot's capabilities, moving the robot along the desired geometric path at speeds calculated for the nominal payload may require torques which exceed the robot's capabilities. In this paper, bounds on joint torque uncertainties are derived in terms of payload uncertainties. Using these bounds, a new trajectory planner is developed to incorporate payload uncertainties such that all the trajectories generated can be realized with given joint torques. Finally, the trajectory planner is applied to the first three joints of the Bendix PACS arm, a cylindrical robot to demonstrate its use and power.     

Dynamic modelling, simulation and control of a manipulator with flexible links and joints

The paper presents a dynamic modelling technique for a manipulator with multiple flexible links and flexible joints, based on a combined Euler–Lagrange formulation and assumed modes method. The resulting generalised model is validated through computer simulations by considering a simplified case study of a two-link flexible manipulator with joint elasticity. Controlling such a manipulator is more complex than controlling one with rigid joints because only a single actuation signal can be applied at each joint and this has to control the flexure of both the joint itself and the link attached to it. To resolve the control complexities associated with such an under-actuated flexible link/flexible joint manipulator, a singularly perturbed model has been formulated and used to design a reduced-order controller. This is shown to stabilise the link and joint vibrations effectively while maintaining good tracking performance.     

Formulation of a Class of Higher Pair Joints in Multibody Systems Using Joint Coordinates

This paper describes the development of general formulations of higher pair joints in multibody systems. A class of higher pair joints, described as a spatial point contact between the surfaces of two interacting bodies is formulated by means of Joint Coordinate Formulation and implemented in a general purpose multibody analysis program. The joint is formulated as remaining within the reduced open loop system according to the notation applied in the Joint Coordinate Method. This representation necessitates an evaluation of the degrees of freedom in the joint. Based on these considerations, the point contact joint is also formulated to cut a loop in the mechanical system. In this case, the appropriate constraint equations and a set of artificial variables are introduced in the analysis. The surfaces in the point contact joint are represented as parametric cubic spline patches but can also be introduced using other methods. Examples illustrating the implemented types of joints are presented at the end of the paper.     

Robustness of decentralized robot controller to payload variation

The decentralized controller for manipulation robot is tested for its robustness to payload variation. First the local controllers are synthesized to withstand variation of inertia round the joints and then the global stability of the robotic system is examined. Three various situations are discussed: a) when actuator inertia is large in comparison to mechanism inertia, b) if the variation of payload is small in comparison to mechanism inertia, and c) if the large variation of payload parameters are expected. An algorithm for testing the robustness of the robot control to parameter variation is established, too. The purpose of the algorithm is to determine the allowable variation of the payload parameters which can be withstood by the simple decentralized controller. On the other hand, by this algorithm the local servosystems can be synthesized which are capable to withstand assumed parameter variation. This synthesis is demonstrated on an example of particular robotic system.     

基于人工肌肉的机器人驱动关节设计与研究

提出一种基于人工肌肉的新型驱动关节设计方法, 用于提高机器人的驱动性能.通过定义关节结构的笛卡儿坐标系统,建立了反映关节结构参 数与工作空间、结构强度、动力学特性之间关系的数学模型.在上述分析的基础上,采用多 目标规划算法对驱动关节进行优化设计,并给出相应的设计变量、目标函数、约束条件和求 解方法.最后,将该方法应用于某四足机器人髋关节的设计过程.仿真结果表明,基于人工 肌肉的新型驱动关节具有良好的强度、灵巧度和承载能力.     

工业机器人负载动力学参数辨识方法

为了解决负载变化导致的机器人控制性能降低的问题,本文在分析负载动力学参数对各关节力矩的影响的基础上,提出了一种仅驱动机器人的第3、4、5、6轴运行激励轨迹的辨识方法．首先,基于最小惯性参数集线性化工业机器人动力学模型;其次,在分析负载参数对各关节力矩的影响的基础上,选取相应的运动关节轴,设计适用于负载辨识的有限项傅里叶级数的优化激励轨迹;然后,在空载和带3种不用负载情况下运行激励轨迹,采集关节角度和关节力矩数据,并将数据通过低通滤波器处理;最后,基于动力学线性模型使用加权最小二乘法辨识负载动力学参数．机器人运行验证轨迹,通过计算负载力矩计算值和测量值的差的均方根（RMS）来评价负载辨识结果．同时将该方法与CAD（computer aided design）方法对比,结果显示前者最多可以将后者RMS值降为原来的16%,且该方法对不同负载辨识结果稳定有效．该方法避免了驱动所有关节轴运动的方式,减小了机器人耦合带来的误差,同时缩短了激励轨迹参数优化时间,有效提高负载动力学参数的辨识效率和效果．     

大型挠性空间机械臂振动抑制的一种关节控制策略

大型空间机械臂在操作过程中,一个突出的问题是超低频挠性,不仅存在机械臂的弯曲振动,而且还存在关节的扭转变形振动;另外一个不能忽视的问题就是减速器的扭矩传递特性,以及机械臂关节运动与基座扰动（空间站）之问的耦合特性,这就要求根据关节结构和传感器配置实现关节位置控制,同时稳定和衰减机械臂及其关节的低频挠性振动．本文运用集中参数法对空间机械臂的挠性动力学进行建模,设计了工程可实现的单个关节控制策略及其控制律,分析和数值仿真了其稳定性,对未来空间站的大型挠性空间机械臂设计、动力学与控制的研究具有一定的参考价值．     

The angular capacity of spherical joints used in mechanisms with closed loops and multiple degrees of freedom

Typical kinematic and dynamic analysis of mechanisms considers the joints just as theoretical constraints. Nevertheless, for some particular kinematic joints (e.g. spherical joints) the physical realization takes the shape of distinct components that are attached to the adjacent bodies. While a spherical joint allows three theoretic relative rotations, except the self rotation of the shaft the other two rotations have a reduced range because of constructive limitations. In this paper we propose a function named angular capacity to represent the range of the physically permitted motion in a spherical joint. A graphical representation of the angular capacity is also proposed to intuitively illustrate the relative motion range and the constructive parameters that influence it are identified. Angular capacity of a spherical joint is defined as a constructive feature of the joint assembly—out of the mechanism context—but also as a motion range demanded by the mechanism from the spherical joint. For the first case general relations have been proposed for the constructive angular capacity calculation and useful consideration has been made for the embodiment design of the spherical joints. For the latter, a complete methodology and relationships for mechanisms with two degrees of mobility are proposed as well. Finally, the suspension-steering mechanism of the passenger cars is presented as a use case.     

Automated sizing of automotive steering ball joints in parametric CAD environment using expert knowledge and feature-based computer-assisted 3D modelling

Ball joints used in the steering systems of vehicles are exposed to fluctuating loads, which can cause fatal accidents in case of failure. The design of ball joints is an iterative and time-consuming process. Even though the automotive industry is preparing for the era of autonomous self-steering vehicles, parts such as ball joints were not designed using a fully automated parametric design methodology. Recently, parametric design of automotive ball joints based on variable design methodology using knowledge and feature-based computer-assisted-3D modelling methods was studied. However, these studies do not give details of the interactive sizing process within the part and assembly module to determine the final dimensions for avoidance of fatigue failure.This work provides methods and discusses details of the configurable sizing of a ball joint assembly under the boundaries of the developed “parametric design platform”. The platform closes the software gap for the automated reconfiguration and sizing of the ball joint assembly using a three-dimensional (3D) modelling technique. The platform can parametrically change part, material, feature, geometry, assembly and dimension features in a programmable environment. It can also reconfigure the ball joint assembly model considering various structured data conforming to technical standards and reasoning mechanisms with “engineering and geometrical relations” provided in this work, and data gathering along the life cycle of a product. Parameterised 3D solid models and a knowledge base of ball joints are stored in a database, and then an evaluation process within the platform that is capable of sizing ball joints for infinite fatigue-life has been established to verify sizing. It demonstrates the practicability and validity of the automated sizing of a steering ball joint within a configurable design environment and with minimum human expert knowledge and interaction.     

改进末端跟随运动的超冗余蛇形臂机器人运动学逆解

针对超冗余蛇形臂机器人运动学逆解中计算量大、超关节极限和位形偏移量大的问题,提出了一种改进末端跟随运动的逆解算法．在末端跟随法中引入蛇形臂弯曲角度的约束,调整关节位置的更新方式,使关节在蛇形臂轴线上运动．通过依次更新关节的空间位置,将超冗余多节蛇形臂的运动学逆解转化为2自由度单节蛇形臂的运动学逆解．仿真分析了蛇形臂机器人在基座移动和基座固定条件下的轨迹跟踪效果,对比了同一目标位置下不同方法的性能．结果表明,改进后的算法能保证蛇形臂的弯曲角度不超过给定范围,关节的运动量从末端到基座依次减小,机器人的运动更协调;与基于雅可比矩阵的数值法和现有启发式方法相比,该方法运算量降低,机器人整体位形偏移量减小,能用于蛇形臂机器人的实时控制．     

两足步行椅机器人的机构设计

主要介绍了两足步行椅机器人的整体机构设计．在踝关节和髋关节处，采用了一种新型多自由度正交关节设计，使得机器人结构紧凑，提高了步态规划的精度．利用两足步行椅机器人动力学模型，分析了各关节的驱动力矩，以此确定了驱动电机的功率．在髋关节和座椅之间设计了减震系统，并建立了减震系统模型，分析了减震系统对于步态稳定性的作用．最后，为保证乘坐者的安全，从机构的角度设计了机械式保护装置．     

气动机器人多指灵巧手——ZJUT Hand

总结了现有灵巧手的缺点,例如结构复杂、难以控制等,并在此基础上提出了一种新型的气动驱动多指灵巧手,命名为ZJUT Hand.基于一种新型的气动柔性驱动器FPA,设计了气动刚柔性弯曲关节及侧摆关节;在此基础上给出了一种4自由度气动拟人手指;为了获得较高的模块化集成度,将5个完全相同的手指装配在拟人手掌上,构成具有5个手指、20个自由度的ZJUT Hand的本体结构;采用仿生学优化方法确定ZJUT Hand的结构参数,并对其本体结构进行了抓持仿真实验.仿真结果表明:ZJUT Hand能够对圆柱、长条形、球形等典型形状的物体实现抓持,并能够模拟人手实现对捏、夹持、勾拉等复杂拟人手形.详细设计了ZJUT Hand的力/位传感系统.完成了ZJUT Hand的抓取实验,结果表明:ZJUT Hand能够对典型形状目标物体实现稳定抓取.最后,简单总结了ZJUT Hand的特色之处.     

Interactive Modeling of Mechanical Objects

Objects with various types of mechanical joints are among the most commonly built. Joints implement a vocabulary of simple constrained motions (kinematic pairs) that can be used to build more complex behaviors. Defining physically correct joint geometry is crucial both for realistic appearance of models during motion, as these are typically the only parts of geometry that stay in contact, and for fabrication. Direct design of joint geometry often requires more effort than the design of the rest of the object geometry, as it requires design of components that stay in precise contact, are aligned with other parts, and allow the desired range of motion. We present an interactive system for creating physically realizable joints with user‐controlled appearance. Our system minimizes or, in most cases, completely eliminates the need for the user to manipulate low‐level geometry of joints. This is achieved by automatically inferring a small number of plausible combinations of joint dimensions, placement and orientation from part geometry, with the user making the final high‐level selection based on object semantic. Through user studies, we demonstrate that functional results with a satisfying appearance can be obtained quickly by users with minimal modeling experience, offering a significant improvement in the time required for joint construction, compared to standard modeling approaches.     

并联微机器人的逆动力学

本文基于牛顿 欧拉法建立了一类PSS副、带柔性铰链的六自由度并联微机器人的 逆动力学方程,这是设计、控制微机器人的前提和基础．所建模型不仅考虑了因柔性铰链的 特殊性,微机器人连杆绕自身轴线转动的内部运动,还分析了柔性球铰弹性变形产生的反力 矩．由于微机器人机构本体以及逆动力学建模过程中所固有的并联特性,对逆动力学可实施 并行算法．最后以一实例进行了仿真分析,仿真结果表明微机器人所需驱动力呈线性变化, 揭示了微机器人在微动情况下的线性本质．