Abstract
Friction stir welding (FSW) has been widely applied in many fields as an alternative to traditional fusion welding. Although serial robots can provide the orientation capability required to weld along curved surfaces, they cannot adequately support the huge axial downward forces that FSW generates. Available parallel mechanism architectures, particularly redundantly actuated architectures for FSW, are still very limited. In this paper, a redundantly actuated 2UPR-2RPU parallel robot for FSW is proposed, where U denotes a universal joint, R denotes a revolute joint and P denotes a prismatic pair. First, its semi-symmetric structure is described. Next, inverse kinematics analysis involving an analytical representation of rotational axes is implemented. Velocity analysis is also conducted, which leads to the formation of a Jacobian matrix. Sensitivity performance is evaluated utilizing level set and convex optimization methods, where the local sensitivity indices are unit consistent, coordinate free, and of definite physical significance. Furthermore, global and hierarchical sensitivity indices are proposed for the design process. Finally, dimension synthesis is conducted based on the sensitivity indices and the optimal link parameters of the parallel robot are obtained. In summary, this paper proposes a dimensional synthesis method for a redundantly actuated parallel robot for FSW based on sensitivity indices.
Highlights
Friction stir welding (FSW) is a novel solid-state welding technology that was patented by The Welding Institute in 1991 [1]
Its advantages over conventional fusion welding processes include the elimination of porosity, low distortion, and no requirement for a filler wire or gas shielding
Eq (26) indicates that optimization begins with max χ1, followed by min χ2, where χi is normalized to a range of zero to one
Summary
The optimal design of an FSW robot based on a 3-PRS parallel mechanism was investigated in Ref. Choi et al [23] proposed an optimization method for torque distribution of redundantly actuated planar parallel mechanisms based on a null-space solution. [42], a convex optimization problem was derived from a six-dimensional one level set problem In this problem, rotation was separated from translation to generate kinematic sensitivity indices with consistent units and clear physical interpretations. The kinematic characteristics of the proposed parallel robot are investigated, followed by sensitivity analysis and dimension optimization, where the sensitivity indices utilized are dimensionally homogeneous, coordinate free, and of clear physical significance.
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