Kinematic modeling of a hydraulically actuated 3-SPR-parallel manipulator for an adaptive shell structure

This paper describes a 3-SPR-parallel robot system with hydraulic actuated prismatic joints that was developed within the context of ongoing research on adaptive shell structures. The potential of adaptive structures is based on the principle of providing means for the system to accommodate a variety of loading conditions (earthquakes, wind, snow) by actively inducing deformations and forces in response to external loads. Thus, stresses and vibrations in the structure are reduced, maintaining or exceeding the performance of passive structures while using much less material and, correspondingly, resources. Adaptive structures, in comparison to traditional systems, contain sensors, actuators, and control systems. One method of actuation is the controlled positioning of the support points of structures. Assuming a statically indeterminate structure, the displacement of the supports will introduce structural deformations and forces. For three-dimensional structures such as the double-curved shell structure under investigation, translational positioning of the support must be provided in all directions. One method to achieve this is the use of 3-SPR-parallel mechanism. The implementation requires a unique and real time solution of the forward and inverse kinematics of the mechanism in order to relate actual displacement of the structural support of the shell to the displacement of the actuators. The solution presented here is based on an analytical approach taking into account the constraint conditions of the 3-SPR-parallel mechanism. The method is validated by numerical analysis of the workspace and then implemented on a reference system.