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Computer vision systems have demonstrated to be useful in applications of autonomous navigation, especially with the use of stereo vision systems for the three-dimensional mapping of the environment. This article presents a novel camera calibration method to improve the accuracy of stereo vision systems for three-dimensional point localization. The proposed camera calibration method uses the least square method to model the error caused by the image digitalization and the lens distortion. To obtain particular three-dimensional point coordinates, the stereo vision systems use the information of two images taken by two different cameras. Then, the system locates the two-dimensional pixel coordinates of the three-dimensional point in both images and coverts them into angles. With the obtained angles, the system finds the three-dimensional point coordinates through a triangulation process. The proposed camera calibration method is applied in the stereo vision systems, and a comparative analysis between the real and calibrated three-dimensional data points is performed to validate the improvements. Moreover, the developed method is compared with three classical calibration methods to analyze their advantages in terms of accuracy with respect to tested methods.

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In this paper, it is proposed a control structure to solve the tracking problem in a class of uncertain mechanical systems. It is considered that the system is affected by unknown disturbances, discontinuous friction and uncertainties. The proposed control algorithm is based on the twisting control algorithm plus a nested signum term, moreover a disturbance estimator is used as feedback to the controller in order to compensate the non modelled parameters and uncertainties of the plant, also a velocity observer is proposed. Through the usage of Lyapunov tools, it is shown that the closed-loop nonlinear system is globally asymptotically stable and achieves zero steadystate position error, also, it is shown that while being asymptotically stable and homogeneous of degree q < 0, these systems approach the equilibrium point in finite time. Numerical simulations and real-time experiments carried out in a mass-spring-damper system show the performance and effectiveness of the control structure.

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In this paper is proposed a control structure for a class of mechanical systems; this structure consists of a continuous controller based on nonsingular terminal sliding mode control plus uncertainty and disturbance estimator. Closed-loop stability is proved by designing an adequate sliding surface and showing the existence of sliding modes by the fulfillment of the reaching law. A controllers comparison using the nonsingular terminal sliding mode, first-order sliding mode, PID, and the proposed control structure is carried out through numerical simulations of a pendulum system, where the l 2 index is used to measure the performance of the controllers. Moreover, real-time experiments are performed in a mechanical system with a pneumatic actuator. The theoretical, numerical, and experimental results validate the feasibility, performance, and robustness of the proposed control structure. INDEX TERMS Mechanical systems, nonsingular terminal sliding mode control, robust control, uncertainty and disturbance estimator.