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Feature Depth Observation for Image-based Visual Servoing: Theory and Experiments

Dipartimento di Informatica e Sistemistica, Università di Roma "La Sapienza", Via Ariosto 25, 00185 Roma, Italy, deluca{at}dis.uniromal.it

Giuseppe Oriolo

Dipartimento di Informatica e Sistemistica, Università di Roma "La Sapienza", Via Ariosto 25, 00185 Roma, Italy, oriolo{at}dis.uniromal.it

Paolo Robuffo Giordano

Dipartimento di Informatica e Sistemistica, Università di Roma "La Sapienza", Via Ariosto 25, 00185 Roma, Italy, robuffo{at}dis.uniromal.it

In the classical image-based visual servoing framework, error signals are directly computed from image feature parameters, allowing, in principle, control schemes to be obtained that need neither a complete three-dimensional (3D) model of the scene nor a perfect camera calibration. However, when the computation of control signals involves the interaction matrix, the current value of some 3D parameters is requiredfor each considered feature, and typically a rough approximation of this value is used. With reference to the case of a point feature, for which the relevant 3D parameter is the depth Z, we propose a visual servoing approach where Z is observed and made available for servoing. This is achieved by interpreting depth as an unmeasurable state with known dynamics, and by building a non-linear observer that asymptotically recovers the actual value of Z for the selected feature. A byproduct of our analysis is the rigorous characterization of camera motions that actually allow such observation. Moreover, in the case of a partially uncalibrated camera, it is possible to exploit complementary camera motions in order to preliminarily estimate the focal length without knowing Z. Simulations and experimental results are presented for a mobile robot with an on-board camera in order to illustrate the benefits of integrating the depth observation within classical visual servoing schemes.

Key Words: Image-Based Visual Servoing • Nonlinear Observers • Depth Observation • Focal Length Observation • Mobile Robots

The International Journal of Robotics Research, Vol. 27, No. 10, 1093-1116 (2008)
DOI: 10.1177/0278364908096706


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