A Modeling and Simulation Platform for Robot Kinematics Aiming Visual Servo Control

Abstract

A robotic system is a mechanical structure built from rigid links connected by flexible joints. The arrangement of links and joints (robot architecture) depends on the task the robot was designed to perform. The robot links have then different shapes and the joints can be of revolute (rotational motion) or prismatic (translation motion) nature. These robots, as described, perform task on an open-loop control scheme, i.e. there is not feedback from the environment (robot workspace) thus it will not notice changes in the workspace. As an attempt to establish a closed-loop control scheme a computer-based vision systems is introduced to detect workspace changes and also to allow guiding the robot (Hutchinson et al., 1996). At the University of Brasilia to cope with the study and teaching of robotics an educational robotic workstation was built around the Rhino XR4 robot (Soares & Casanova Alcalde, 2006). To implement a vision-guided robot a video camera was installed and integrated to the robot control system. As an alternative for dealing with the real system and for teaching purposes a simulation platform was devised within the Matlab environment (Soares & Casanova Alcalde, 2006). The platform was called RobSim and it is based on assembling elementary units (primitives) which represent the robot links, being the joints represented by the motion they perform. This simulation and developing platform then evolved and now it includes robot visual servo control being presented in this work. Within RobSim platform control algorithms can be developed for the vision-guided robot to perform tasks before implementing them on the real system. Simulation tools for either conventional robotic systems (Legnani, 2005; Corke, 1996) and for vision-based systems (Cervera, 2003) do exist, this work presents a unified environment for both systems. The developed simulation tools were assembled as a laboratory platform, where robotic and vision-based algorithms share similar data structures and block building methodologies. Moreover, this platform was developed mainly for educational purposes; later on it was found it can be used for research and design of robotic systems. The graphical presentation is as simple as possible, but allowing an insight and visualization of parts and motions. The chapter is organized as follows; initially the RobSim basic mounting blocks, the primitives, are defined and described. Then, the RobSim developed Matlab functions for initialization, motion, computer display and image acquisition are presented. Following, the modeling and simulation capabilities RobSim platform offers are presented together with