Design of a Gough-Stewart Platform Based on Visual Servoing Controller

Designing a robot with the best accuracy is always an attractive research direction in the robotics community. In order to create a Gough-Stewart platform with guaranteed accuracy performance for a dedicated controller, this paper describes a novel advanced optimal design methodology: control-based design methodology. This advanced optimal design method considers the controller positioning accuracy in the design process for getting the optimal geometric parameters of the robot. In this paper, three types of visual servoing controllers are applied to control the motions of the Gough-Stewart platform: leg-direction-based visual servoing, line-based visual servoing, and image moment visual servoing. Depending on these controllers, the positioning error models considering the camera observation error together with the controller singularities are analyzed. In the next step, the optimization problems are formulated in order to get the optimal geometric parameters of the robot and the placement of the camera for the Gough-Stewart platform for each type of controller. Then, we perform co-simulations on the three optimized Gough-Stewart platforms in order to test the positioning accuracy and the robustness with respect to the manufacturing errors. It turns out that the optimal control-based design methodology helps get both the optimum design parameters of the robot and the performance of the controller {robot + dedicated controller}.

Contribution to generic modeling and vision-based control of a broad class of fully parallel robots

This paper deals with a generic modeling and vision-based control approach for a broad class of parallel mechanisms. First, a generic architecture representing several families is proposed. Second, inspired by the geometry of lines, a generic differential inverse kinematic model according to the proposed generic structure is introduced. Finally, based on the image projection of cylindrical legs, a kinematic vision-based control using legs observation is presented. The approach is illustrated and validated on the Gough–Stewart and Par4 parallel robots.

Image-based Visual Servoing of a Gough—Stewart Parallel Manipulator using Leg Observations

In this paper, a tight coupling between computer vision and parallel robotics is exhibited through the projective line geometry. Indeed, contrary to the usual methodology where the robot is modeled independently from the control law that will be implemented, the proposed method takes into account, from the early modeling stage, the fact that vision will be used for control. Hence, kinematic modeling and projective geometry are fused into a control-devoted projective kinematic model. Thus, starting from a vision-based kinematic modeling of a Gough—Stewart manipulator, a visual servoing scheme is presented, where the image projection (edges) of the non-rigidly linked legs are servoed, rather than the end-effector pose or the leg directions.

Laser steering using virtual trifocal visual servoing

This paper focuses on the development of a weakly calibrated three-view-based visual servoing control law applied to the laser steering process. It proposes to revisit the conventional trifocal constraints governing a three-view geometry for a more suitable use in the design of an efficient trifocal vision-based control. Thereby, an explicit control law is derived, without any matrix inversion, which allows to simply prove the global exponential stability of the control. Moreover, only ‘[Formula: see text]’ are necessary to design a fast trifocal control system. Thanks to the simplicity of the implementation, our control law is fast, accurate, robust to errors on the weak calibration and it exhibits good behavior in terms of convergence and decoupling. This was demonstrated by different experimental validations performed on a test-bench for the steering of laser spot on a 2D and 3D surface using a two degrees-of-freedom commercial piezoelectric mirror, as well as in preliminary cadaver trials using an endoluminal micromirror prototype.