Vision-based 2D and 3D Control of Robot Manipulators

Abstract

Robotics has been a paradigm for science in the last few decades. At first, scientists’ efforts were devoted to the solution of the problem of planning and control of themotion of robot manipulators. However, the motion control of robot manipulators in unstructured environments is today an attractive scientific problem. An interesting solution for motion control is the use of sensor information, such as computer vision, in the system’s feedback. Several works and tools have been developed in recent years in this field (Corke; 2005), (Chaumette and Hutchinson; 2006). The more typical approaches consider visual perception for servoing and for the so called look and move (Hutchinson et al.; 1996). Visual servoing (Kelly et al.; 2000) can be classified into two approaches: camera-in-hand or camera-to-hand (Flandin et al.; 2000). In camera-to-hand robotic systems, multiple cameras or a single camera fixed in the worldcoordinate frame capture images of both, the robot and its environment. The tracking of the object with visual feedback can be made in 2D or 3D. An interesting solution for the visual servoing of camera-in hand robot manipulators in 2D can be found in e. g. (Bonfe et al.; 2002) and (Hernandez et al.; 2008) where stability demonstration of a decoupled controller have been presented. For 3D tracking some solutions reported are look and move controller, with one camera (Sim et al.; 2002) or more than one camera (Xie et al.; 2005). A 3D visual servoing with stability analysis in continuous time is presented by (Hernandez et al.; 2008a) and (Kelly et al.; 2006) present a direct visual servoing with transpose Jacobian control technique for regulation of robot manipulators in the 3D Cartesian space. In a similar vein (Enescu et al.; 2006) present mobile robot navigation for person tracking using a stereo head-camera. In this chapter, we consider the control problem of camera-in-hand robot manipulators in 2D and 3D. In both cases only one camera is mounted on the robot’s arm, which supplies visual information of the environment, with the aim of moving the manipulator by maintaining the image of the tracked object (a sphere) in the centre of the image plane, despite the possible movements of the object. In the 3D control the constant radius is used as a feature too. In this work, the proposed control system considers two loops in cascade, an internal loop solving the robots’ joint control, and an external loop implementing a dynamic look and move visual controller. A stability analysis in discrete time is developed under the conditions that it is possible to approximate the dynamic effect of the internal loop as an external loop time delay (Corke; 1996) and (Bonfe et al.; 2002). The more classic presentations of servovisual control are velocity controllers, based in the term feature Jacobian,(Chaumette and Hutchinson; 2006) 2