Showing papers by "Gonzalo López-Nicolás published in 2007"

Homography-Based Visual Control of Nonholonomic Vehicles

Abstract: This paper presents a new visual control approach based on homography. The method is intended for nonholonomic vehicles with a fixed monocular system on board. The idea of visual control used here is the usual approach where the desired position of the robot is given by a target image taken at that position. This target image is the only previous information needed by the control law to perform the navigation from the initial position to the target. The control law is designed by the input-output linearization of the system using elements of the homography as output. The contribution is a controller that deals with the nonholonomic constraints of the mobile platform needing neither decomposition of the homography nor depth estimation to the target.

Switched Homography-Based Visual Control of Differential Drive Vehicles with Field-of-View Constraints

Abstract: This paper presents a switched homography-based visual control for differential drive vehicles. The goal is defined by an image taken at the desired position, which is the only previous information needed from the scene. The control takes into account the field-of-view constraints of the vision system through the specific design of the paths with optimality criteria. The optimal paths consist of straight lines and curves that saturate the sensor viewing angle. We present the controls that move the robot along these paths based on the convergence of the elements of the homography matrix. Our contribution is the design of the switched homography-based control, following optimal paths guaranteeing the visibility of the target.

Shortest Path Homography-Based Visual Control for Differential Drive Robots

Abstract: It is generally accepted that machine vision is one of the most important sensory modalities for navigation purposes. Visual control, also called visual servoing, is a very extensive and mature field of research where many important contributions have been presented in the last decade [Malis et al.,1999, Corke and Hutchinson, 2001, Conticelli and Allotta, 2001, Tsakiris et al., 1998, Ma et al., 1999]. Two interesting surveys on this topic are [De Souza and Kak, 2002] and [Hutchinson et al., 1996]. In this work we present a new visual servoing approach for mobile robots with a fixed monocular system on board. The idea of visual servoing is used here in the sense of homing, where the desired robot position is defined by a target image taken at that position. Using the images taken during the navigation the robot is led to the target. A traditional approach is to perform the motion by using the epipolar geometry [Basri et al., 1999, Rives, 2000, Lopez-Nicolas et al., 2006]. These approaches have as drawback that the estimation of the epipolar geometry becomes ill conditioned with short baseline or planar scenes, which are usual in human environments. A natural way to overcome this problem is using the homography model. In [Malis and Chaumette, 2000] it is proposed a method based on the estimation of the homography matrix related to a virtual plane attached to an object. This method provides a more stable estimation when the epipolar geometry degenerates. In [Benhimane et al., 2005] it is presented a visual tracking system for car platooning by estimating the homography between a selected reference template attached to the leading vehicle. A significant issue with monocular camera-based vision systems is the lack of depth information. In [Fang et al., 2005] it is proposed the asymptotic regulation of the position and orientation of a mobile robot by exploiting homography-based visual servo control strategies, where the unknown time-varying depth information is related to a constant depth-related parameter. These homography-based methods usually require the homography decomposition, which is not a trivial issue. Two examples of approaches which do not use the decomposition of the homography are [Sagues and Guerrero, 2005] which is based on a 2D homography and [Benhimane and Malis, 2006] which presents an uncalibrated approach for manipulators. We present a novel homography-based approach by performing the control directly on the