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Kinematic design and analysis of a 7 degree-of-freedom dual-stage inspection manipulator for dexterous subsea applications

Remotely operated Underwater Robotic Vehicles (URV) are widely used for subsea tasks such as cleaning, repair and inspection of long objects such as pipelines. The ability to perform such inspections by a remotely located human pilot, over extended periods, is highly desirable. Due to underwater currents and the inability to maintain a fixed distance from the object, produces a constantly varying image for the observer. Incorporation of stereoscopic imaging, with the option of maintaining a constant image size, was perceived to be desirable. This effect was implemented by dynamic compensation of the camera zoom, and shown to negate the negative motion effects and allowed the operator to perform close inspection for extended periods of time.This paper describes the design, structure, and preliminary evaluation of an experimental Telepresence Viewing System (TVS) for Underwater Robotic Vehicle (URV) to enhance the observation capabilities of its remote pilot during an inspection task. The Telepresence Viewing System enables an automatic projection of suitably prepared and adapted underwater stereoscopic video images from the video cameras of the URV, into the operator's visual field. The processed images aid the coupling of the operator's vestibular and kinesthetic sensations to the visual information from the URV.

The optimum dimensioning of an underwater inspection manipulator is discussed in this paper. The inspection of a weld seam using an alternating current eld measurement (ACFM ) probe was identi ed as a ve-dimensional Cartesian task. Due to the forward positioning of the required workspace, this manipulator requires two additional axes to locate its base with respect to the weld seam. This leads to a seven-axis manipulator, comprising a two-axis launching stage and a ve-axis dexterous inspection stage. The optimization of the architecture of the latter ve-axis inspection manipulator is the subject of this paper. In optimizing the architecture, various postures of the manipulator during the inspection process were considered, which thus allows identi cation of the limiting values of the joint angles for maximum dexterity. The optimum link lengths to ensure the highest dexterity were then determined from the results of the analysis. It is shown that the weld seam diameter and the manipulator condition number can be used as the deciding parameters for determining the relative link lengths of the ve-axis inspection stage of the manipulator.

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