Workspace Analysis of 7-DOF Humanoid Robotic Arm

Abstract

The 7-DOF humanoid robotic arm joint coordinate systems are established and link parameters are determined by D-H method, and the robotic arm kinematics model is established. The position and orientation of robotic arm end-effector is generated by homogeneous transform method. Monte Carlo method is proposed in analyzing the workspace of robotic arm and the echogram of robotic arm is calculated based on mapping relation from joint space to workspace of robotic arm. The reference basis is provided for follow-up robot trajectory planning, dynamics analysis, and motion control and parameter optimization. Introduction High-tech robot technology combines a variety of disciplines, such as computer, control theory, mechanisms, information and sensor technology, artificial intelligence and bionics, and it is very active in contemporary research and widely used in the fields. Compared with other robotic arms, humanoid robotic arm has a high degree of adaptability and flexibility, and it concretely performs in low requirements for environment, flexible motion and low energy consumption. Humanoid robotic arm has become one of the most active research direction in robot field and is a hot research for scholars from various countries. It will be surely the latest development trend and direction of modern manufacturing automation [1, . The flexibility of robotic arm plays a vital role in its work ability. Workspace is an important kinematics index for measuring the movement flexibility degree of robotic arm, it refers to the point coordinate that robotic arm end-effector can reach in space. Currently, the solution methods about robotic arm workspace are mainly graphical method, analytical and numerical methods. Graphic method and analytic method are restricted by the number of joints and they can’t accurately describe some robotic arms. The calculated amount of numerical method is too large and the reliability can’t be guaranteed for some boundary surfaces [3, . Monte Carlo method is used in this paper, derives from the numerical method and bases on random probability algorithm. With the rapid development of computer technology, Monte Carlo method has been more widely used . In this paper, the 7-DOF humanoid robotic arm is studied. Its kinematic model is established by D-H method and the position and orientation of robotic arm end-effector is generated. The workspace of humanoid robotic arm is analyzed in MATLAB environment by D-H method. Structure and modeling approach Workspace is the robot end-effector work area that is according to robotic configuration and the size of link and wrist joint, the point set robot can reach. It is the important indicator for measuring mechanism function, and it is very significant for mechanism design, control and operate. It can be determined by mathematic equations, and these equations define the constraint conditions of robotic links and joints. Accessible workspace refers to all points set that the end-effector reference point can reach and it doesn’t consider the position and orientation of end-effector. The structure and its link parameters. The 7-DOF humanoid robotic arm consists of shoulder joint, elbow joint and wrist joint. The shoulder joint with three degrees of freedom, the elbow joint with a degree of freedom and the wrist joint with three degrees of freedom, and the structure model is International Conference on Intelligent Systems Research and Mechatronics Engineering (ISRME 2015) © 2015. The authors Published by Atlantis Press 1560 shown in Fig.1. Shoulder joint and elbow joint are used to determine the spatial position, and wrist joint is used to determine the position and orientation of robotic arm. D-H model describes a very simple method for establishing the model about the links and the joints of robot, and it can be used in any robotic configurations regardless of robot structure sequence and complexity. In order to describe the motion relationship of robot arm adjacent links, the kinematics model is established by the D-H method for the robotic arm shown in Fig.1 and the robot each joint reference coordinate system is established. The coordinate system is shown in Fig.2 and the D-H parameters are shown in Table 1. Where, θi is the joint variable, θimin for joint variable lower limit and θimax for joint variable ceiling, di, and αi-1and ai-1 are three fixed link parameters. Fig. 1 The humanoid robotic arm structure model Fig. 2 The humanoid robotic arm link coordinates Table1 The 7-DOF humanoid robotic arm D-H parameters table i θi di/(mm) αi-1/(°) ai-1/(mm) θimin/(°) θimax/(°) 1 θ1 d1=410 0 0 -180 180 2 θ2 0 90 0 -110 110 3 θ3 d3=490 -90 0 -170 170 4 θ4 0 90 0 -130 130 5 θ5 d5=420 -90 0 -180 180 6 θ6 0 90 0 -110 110 7 θ7 d7=180 -90 0 -180 180 Forward kinematics analysis. Robot kinematics analysis is a prerequisite for robotics technology research and is also the foundation for robot workspace analysis and motion control. Robotic arm forward kinematics analysis is: robotic arm link geometry parameters and joint angle vectors are known, and calculating the position and orientation of robotic arm end-effectors relative to the reference coordinate system. The position and orientation transformation matrix from robotic adjacent joint coordinate system i-1 to i is as equation (1).