Motion Study of the Ornithopter with Periodic Wing Oscillations

The motion of an ornithopter, a flying robot, consisting of a body and two symmetric twolink wings, is considered. The device moves in a vertical plane perpendicular to the longitudinal axis of the robot. All the links of the object form a chain through cylindrical joints with parallel axes. A mathematical model of the ornithopter is developed based on a bird’s flight analysis taking into account the aerodynamic interaction of all the links with the environment. Sequences of flight phases are considered, each of which differs in the direction of motion of the wing links. As a result of numerical simulation, diagrams of the robot’s modes of motion are constructed (ascent, hovering, and descent) and the effect of the amplitude and frequency of oscillation of the wing links, as well as their area, is determined (the same wing area was achieved by varying the length and width of the wings).     

Motion analysis of a tripod parallel mechanism

A tripod parallel mechanism consists of three links of fixed length and a rigid platform, and these are connected by revolute joints. The platform can achieve sixdegrees-of-freedom (6-DOF) motion by the coordinated movement of the bottom ends of the three links on a horizontal plane. This mechanism has advantages over the more common six extendible parallel manipulators. It has a much larger work space and a simple structure. In this article, we show that the vector analysis for this tripod parallel mechanism and the derivation of the positions of the three bottom ends of the links in an arbitrary attitude of platform can be found by inverse kinematics and the conditions of geometrical constraint. Then, by a numerical simulation, the trajectories of the bottom ends of the three links are shown.     

A constrained assumed modes method for dynamics of a flexible planar serial robot with prismatic joints

In the present study, for the first time, flexible multibody dynamics for a three-link serial robot with two flexible links having active prismatic joints is presented using an approximate analytical method. Transverse vibrations of flexible links/beams with prismatic joints have complicated differential equations. This complexity is mostly due to axial motion of the links. In this study, first, vibration analysis of a flexible link sliding through an active prismatic joint having translational motion is considered. A rigid-body coordinate system is used, which aids in obtaining a new and rather simple form of the kinematic differential equation without the loss of generality. Next, the analysis is extended to include dynamic forces for a three-link planar serial robot called PPP (Prismatic, Prismatic, Prismatic), in which all joints are prismatic and active. The robot has a rigid first link but flexible second and third links. To model the prismatic joint, time-variant constraints are written, and a motion equation in a form of virtual displacement and virtual work of forces/moments is obtained. Finally, an approximate analytical method called the “constrained assumed modes method” is presented for solving the motion equations. For a numerical case study, approximate analytical results are compared with finite element results, which show that the two solutions closely follow each other.     

3-RRRT并联机器人位置正向求解研究

研究一种3-RRRT型并联机器人机构的运动学正向求解方法。根据3-RRRT型并联机器人机构特点以及关节运动的取值范围,提出了以并联机器人支链中支杆的方向余弦和动平台绝对位置坐标为系统的广义坐标的方法,并详细地推导了3-RRRT型并联机器人运动学模型,通过进一步消除中间变量的方法最终获得了易于正、逆运动学求解的只包含3个驱动关节坐标与动平台3个绝对位置坐标的约束方程组。最后,运用基于Moore—Penwse广义逆的牛顿迭代格式编制了MATLAB运动学正向求解程序,并进行了运动学正向求解数值仿真,结果表明求解程序快速有效。     

Design and analysis of the statically balanced direct-drive robot manipulator

A practical architecture, using a four-bar linkage, is considered for the University of Minnesota direct-drive robot (Kazerooni, H., Kim, S.: A new architecture for direct drive robots. In Proc. IEEE International Conference on Robotics and Automation, Philadelphia, Pennsylvania, April 1988). This statically balanced direct-drive robot has been constructed for stability analysis of the robot in constrained manipulation (Kazerooni, H. et al.: Fundamentals of robust compliant motion for robot manipulators. IEEE J. Robotics Automation 2: 1986; Kazerooni, H.: On the robot compliant motion control. ASME J. Dynamic Systems Msmt Control; 111 (3): September 1989. Kazerooni, H. et al.: Theory and experiments on robot compliant motion control. ASME J. Dynamic Systems Msmt Control, June 1990). As a result of the elimination of the gravity forces (without any counterweights), smaller actuators and, consequently, smaller amplifiers were chosen. The motors yield acceleration of 5 g at the robot end point without overheating. High torque, low speed, brushless AC synchronous motors are used to power the robot. Graphite-epoxy composite material is used for construction of the robot links. A 4-node parallel processor has been used to control the robot. A compliant motion control method has been derived and experimentally verified to guarantee stable constrained maneuvers for the robot. As part of the research work, a general criterion has been derived to guarantee the stability of robot manipulators in constrained maneuvers.     

SYMBOLIC COMPUTATION OF ROBOT DYNAMIC PARAMETERS

Optimal performance of robot manipulators can be achieved only by utilizing advanced control algorithms. However, precise control of robot motion requires the use of accurate dynamic models, which are very complicated due to varying arm geometric configuration, uncertain effects of load handling on the dynamic stability of the arm, and the high degree of nonlinearty and coupling exhibited between different links. Therefore, an efficient and fast method for on-line tuning of robot dynamic parameters must be devised. In this work a simplified model based on Lagrange-Euler dynamics is developed. The proposed method is simple and systematic for the extraction and identification of robot dynamic parameters. The dynamic parameters are then formulated as a regression model. This model is used to generate the closed-form solution of the dynamics. The analysis in this work is based on a set of compiled data for the Stanford arm to facilitate the study of the dynamic performance and closed-loop solutions of robot manipulators. For the derivation of the dynamics MAPLE (symbolic computer algebra language) is used.     

Recursive modelling in dynamics of Agile Wrist spherical parallel robot

Recursive matrix relations for kinematics and dynamics of the 3-RRR Agile Wrist spherical parallel robot are established in this paper. The prototype of the robot is a three-degrees-of-freedom mechanism with three identical legs. Controlled by concurrent torques, which are generated by some electric motors, the active elements of the robot have three independent rotations. Knowing the rotation motion of the moving platform, we develop first the inverse kinematical problem and determine the velocities and accelerations. Further, the principle of virtual work is used in the inverse dynamic problem. Matrix equations offer iterative expressions and graphs for the power requirement comparison of each of three actuators in two computational complexities: complete dynamic model and simplified dynamic model.     

Cable-direct-driven-robot (CDDR) with a 3-link passive serial support

Cable-direct-driven-robots (CDDRs) provided with a passive serial support represent an interesting and rising evolution of planar cable robots. The paper is devoted to present and analyze a novel CDDR robot. The robot consists in a fully actuated CDDR supported against loading normal to the motion plane with a 3-link passive planar serial manipulator. This hybrid structure combines positive features of both parallel and serial architectures, and prevents out-of-plane movements without the necessity for the robot to be supported on the motion plane. The adoption of a 3-link serial manipulator ensures a greater workspace area compared with similar structures that adopt a smaller number of links, and improves specific characteristics of their dynamics. Nevertheless undesired oscillations may occur since the serial manipulator is underconstrained. For this reason damping elements are inserted in the structure. Simulation examples are presented to demonstrate the novel CDDR concept and its dynamics. In addition, a strategy to select proper values of damping coefficients is presented.     

Inverse dynamics of the 3-PRR planar parallel robot

Recursive modelling for the kinematics and dynamics of the known 3-PRR planar parallel robot is established in this paper. Three identical planar legs connecting to the moving platform are located in a vertical plane. Knowing the motion of the platform, we develop first the inverse kinematics and determine the positions, velocities and accelerations of the robot. Further, the principle of virtual work is used in the inverse dynamics problem. Several matrix equations offer iterative expressions and graphs for the power requirement comparison of each of three actuators in two different actuation schemes: prismatic actuators and revolute actuators. For the same evolution of the moving platform in the vertical plane, the power distribution upon the three actuators depends on the actuating configuration, but the total power absorbed by the set of three actuators is the same, at any instant, for both driving systems. The study of the dynamics of the parallel mechanisms is done mainly to solve successfully the control of the motion of such robotic systems.     

A neural network-based approach for an assembly cell control

In several robotics applications, the robot must interact with the workspace, and thus its motion is constrained by the task. In this case, pure position control will be ineffective since forces appearing during the contacts must also be controlled. However, simultaneous position and force control called hybrid control is then required. Moreover, the nonlinear plant dynamics, the complexity of the dynamic parameters determination and computation constraints makes more difficult the synthesis of control laws. In order to satisfy all these constraints, an effective hybrid force/position approach based on artificial neural networks for multi-inputs/multi-outputs systems is proposed. This approach realizes, simultaneously, an identification and control of systems, and it is implemented according to two phases: At first, a neural observer is trained off-line on the basis of the data acquired during contact motion, in order to realize a smooth transition from free to contact motion. Then, an online learning of the neural controller is implemented using neural observer parameters so that the closed-loop system maintains a good performance and compensates for uncertain/unknown dynamics of the robot and the environment. A typical example on which we shall focus is an assembly task. Experimental results on a C5 links parallel robot demonstrate that the robot's skill improves effectively and the force control performances are satisfactory, even if the dynamics of the robot and the environment change.     

机械臂惯性矩阵的并行计算

本文在给出一种非递推形式的逆动力学计算公式的基础上，针对机械臂惯性矩阵的计算提出了一种面向Ｏ（ｎ）个处理器的并行算法，并以ＰＵＭＡ５６０机器人的前３个臂为例进行了计算效率分析。     

A systematic formulation of dynamic equations for robot manipulators with elastic links

Although a variety of formulation schemes for the dynamic equations of robot manipulators with rigid links can be found in the literature, an efficient method of the formulation for robot manipulators with elastic links is not well known. Accordingly, this work presents the derivation of the equations of motion for application to mechanical manipulators with elastic links. The formulation is conducted analytically using Hamilton's principle. The resultant equations consist of the terms of inertial, Coriolis, centrifugal, gravitational, and exerted forces. They are expressed in terms of a set of independent generalized coordinates. In contrast to conventional variational approaches, the present method provides an efficient and systematic way for obtaining the compact symbolic equations of flexible manipulator systems. Two examples are presented to illustrate the proposed methodology. Firstly, a three-link flexible manipulator with three revolute joints is studied. A flexible manipulator consisting of a prismatic joint and a discrete mass is the second model.     

Methodology for the kinematical selection of a manipulator for a specified task

Manipulator design methodology is a recent and important issue in the robot design research area. Most importantly, to design a robot rationally, one must have a strong understanding of the design parameters of the manipulator, and of the characteristics of the robot relative to its kinematical and dynamical requirements. Development of a robot capable of fast movements or high payloads is progressed by the analysis of dynamic characteristics, DOF positioning, actuator selection, structure of links, and so on. This paper highlights the design of a robot manipulator scaled down from its final form, when it will passively be handled by a human for man-machine cooperation. The requirements of the system include its having 6-DOF and the capacity for a high payload in the condition of its maximum reach. The primary investigation factors are motion range, performance within the motion area, and reliability during the handling of heavy materials. Traditionally, the mechanical design of robots has been viewed as a problem of packaging motors and electronics into a reasonable structure. This process usually transpires with heavy reliance on designer experience. Not surprisingly, the traditional design process contains no formally defined rules for achieving desirable results, as there is little opportunity for quantitative feedback during the formative stages. This work primarily focuses on the selection of proper joint types and link lengths, considering a specific task type and motion requirements of the curtain wall installation process in the construction site based on the result of experiment of proto type system of this study.     

Swing-Up Control for a 3-DOF Gymnastic Robot With Passive First Joint: Design and Analysis

This paper concerns a swing-up control problem for a three-link gymnastic planar robot in a vertical plane with its first joint being passive (unactuated) and the rest being active (actuated). The objectives of this paper are to: (1) design a controller under which the robot can be brought into any arbitrarily small neighborhood of the upright equilibrium point, where all three links of the robot remain in their upright positions; and (2) attain a global analysis of the motion of the robot under the controller. To tailor the energy-based control approach to achieve the aforementioned objectives, first, this paper considers the links 2 and 3 as a virtually composite link, and proposes a coordinate transformation of the angles of active joints. Second, this paper constructs a novel Lyapunov function based on the transformation, and devises an energy-based swing-up controller. Third, this paper carries out a global analysis of the motion of the robot under the controller, and establishes some conditions on control parameters for achieving the swing-up control objective. To validate the theoretical results obtained, this paper provides simulation results for a three-link robot with its mechanical parameters being obtained from a human gymnast.     

Dimensional synthesis of a three translational degrees of freedom parallel robot while considering kinematic anisotropic property

By taking the Delta robot as the object of study, this paper deals with the methodology of the dimensional synthesis of the three translational degrees of freedom parallel robot while considering the kinematic anisotropic property. The velocity transmission index is employed as the objective function of the optimization design. The physical meaning of the velocity transmission index is the maximum of the input angular velocity when the moving platform translates with an assigned velocity. The determinant of the direct kinematic Jacobian matrix, the ratio of the machine volume to that of the desired workspace and the difference between the radius of the base and the radius of the moving platform are adopted as the constraints for the dimensional synthesis in order to make the Delta robot have a good transmission behavior between the distal links, keep far away from the direct kinematic singular configuration, not to be a very tall and slender configuration, achieve the desired performance without large dimension and big building cost. The example of the dimensional synthesis of the Delta robot is presented in the simulation while considering the maximum velocity requirements for the moving platform along the respective direction parallel to the x axis, y axis and z axis are varied. The conclusions are provided at the end of the paper.     

一种并联激光焊接机器人的机构设计与运动学分析

提出了一种3 分支5 自由度的并联激光焊接机器人,通过3 个分支共同作用,使整机具备了5 个自由 度的空间加工能力．针对激光焊接,通过分析该机器人的结构特性,建立了其正反解运动学模型,通过解析法求解 该模型并进行了计算仿真．最后,对机器人进行激光拼焊实验,仿真数据和实验结果表明,本文研究的并联机器人 机构适用于实际的高速、高精度激光焊接．     

Quadruped walking with parallel link legs

We are proposing an underwater robot for the work. In this study, we designed the robot, which has body of rectangular plane and 4 legs at each corner. The leg is consisted with parallel mechanism of 2or3 cylinders, and the end of each cylinder is attached on the robot body with free rotational joint and the end of both piston rods are connected with pin joint. 2 cylinder leg’s motion is restricted in forward or backward direction but 3 cylinder leg can move any direction. We are studying the control scheme of walking for this robot, which is putting mind especially on smooth and steady movement without rolling, pitching, yawing or heaving motion and keeping the body horizontally. We confirmed the validity of control scheme with simulation and experiments.     

Dynamics and elasto-dynamics optimization of a 2-DOF planar parallel pick-and-place robot with flexible links

Dynamic modeling and analysis of a 2-DOF translational parallel robot with flexible links for high-speed pick-and-place operation is presented in this paper. Optimization is implemented with the goal to improve the dynamic accuracy of the end-effector at high speed. The governing equations of flexible links within the robot are formulated in the floating reference frame using Euler–Lagrange method, leading to a global FEM model being generated using the KED (Kineto-Elasto-Dynamics) technique. The dynamic characteristics of the robot are then investigated by model analysis. A numerical dynamic index is proposed to identity the range of natural frequency when the robot reaches different configurations. The comparisons are made between the optimized and original designs in terms of dynamic stress and response.     

基于Pro/E二自由度并联机器人的结构设计

为了提高研发效率,需要将机器人的设计过程和分析过程集成起来;针对这一集成要求,提出了基于Pro/E二自由度的机器人仿真平台,并建立两自由度平移运动并联机器人运动仿真模型;验证了机构的实际工作空间和运动情况,指出了该机构的在实际中的应用;最后通过仿真了机器人的位置轨迹、速度轨迹以及加速度轨迹来验证,文章所设计的二自由度机器人性能良好、工作灵活,很好地满足了设计指标要求,具有一定的实用性。     

Modeling, simulation and fuzzy control of an anthropomorphic robot arm by using Dymola

Analysis and fuzzy control of an anthropomorphic robot arm on a special trajectory is the subject of this paper. These types of systems are used in cutting operations on materials, joining materials by welding, material handling in remote and dangerous environments, packing of foods, inspection/testing electronic parts or medical products. This robot arm realizes the handling motion on a special trajectory. In this study, the first three links of Mitsubishi RV-2AJ Industrial Robot, are like an anthropomorphic arm, have been modeled and simulated by using Dymola. Kinematic equations have been obtained and mathematical model of this system has been formed by using Lagrange’s Equations. Fuzzy logic controller for the joint angles for the motion trajectory has been designed and the simulation results have been presented at the end of the study.