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Chapter 16
Points-based Visual Servoing with Central
Cameras
Hicham Hadj-Abdelkader, Youcef Mezouar, and Philippe Martinet
Abstract. This chapter concerns hybrid visual servoing schemes from a set of points
viewed by central camera. The main purpose is to decouple the velocity commands
in order to obtain an adequate camera trajectory. The proposed schemes are model-
free since they are based on the homography matrix between two views. The ro-
tational motions are controlled using the estimated orientation between the current
and the desired positions of the robot, while the translational motions are controlled
using the combination between image points (onto the sphere or into the normalized
plane) and 3D information extracted from the homography matrix. Real-time exper-
imental results with a cartesian manipulator robot are presented and show clearly
the decoupling properties of the proposed approaches.
16.1
Introduction
In vision-based control, the choice of the set of visual features to be used in the con-
trol scheme is still an open question, despite of the large quantity of results obtained
in the last few years. The visual servoing schemes can be classified in three groups:
position-based visual servoing (PBVS) [27], image-based visual servoing (IBVS)
[7] and hybrid visual servoing [15]. In PBVS, the used information is defined in
the 3D space which allow the control scheme to ensure nice decoupling properties
between the degrees of freedom (DOF) (refer to [26]). Adequate 3D trajectories can
thus be obtained such as a geodesic for the rotational motion and a straight line
for the translational motion. However, this kind of control scheme is sensitive to
measurement noises and the control may thus suffer from potential instabilities [3].
In IBVS the control is performed in the image space. Whatever the nature of the
possible measures extracted from the image, the main question is how to combine
them to obtain an adequate behavior of the system. In most works, the combination
of different features is nothing but a simple stacking. If the error between the initial
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