A kinematic optimization procedure for redundantly actuated parallel manipulator is developed to ensure the isotropic antagonistic stiffness in a workspace. The kinematic parameters of the mechanism are optimized to maximize and equal out antagonistic stiffness of the redundantly actuated manipulator when size and shape of the usable workspace are given but position in the entire workspace is not. The proposed procedure is verified with a 2-DOF planar manipulator by experiments. The experimental results show that the proposed procedure is useful for designing the redundantly actuated parallel manipulator with isotropic antagonistic stiffness in a predefined usable workspace as a design constraint.

In this paper, two torque assignment methods of the antagonistic stiffness for a 2-DOF planar parallel manipulator are presented and verified by experiments. The first method is equalizing the magnitude of the stiffness in all directions at a desired position. The second method is maximizing the active stiffness in one direction at a given path. A 2-DOF parallel mechanism with four actuators is used for verification tests, where the internal torque of the mechanism exists on the two dimensional null space. In the experiment, passive and active stiffness are tested when endowing the external force at the moving platform and compared with the estimated results.

Welding is very difficult and dangerous for manual welders. The double hull structures found in ships are very hazardous environments, and as such the shipbuilding industry demands a safer, autonomous system to perform the welding rather than deploy manual welders. This paper describes the design of a new mechanism, called the 'Rail Runner', which is able to autonomously travel within the double hull structure. The design of a 3P3R serial manipulator for welding is also described in this paper. As an application of the 'Rail Runner' mechanism, we combine the 'Rail Runner' platform and the 3P3R serial manipulator for autonomous welding. The mechanical system of this robot is composed of a six-axes (3P3R) manipulator for achieving the welding function and a six-axes mobile platform for traveling within the double hull structure. This robot is able to autonomously travel between longitudinal structures, with transverse direction, and is capable of welding in double hull structures. The 'Rail Runner' can raise the efficiency of the welding process, as compared to manual welders. This in turn raises the international competitiveness of the shipbuilding industry.