Elastodynamic optimization of a 3T1R parallel manipulator

In this paper the elastodynamic optimization of a 3T1R parallel manipulator is performed. The robot is first divided into subsystems including its four legs and the moving platform; then, each leg is split into three modules. A module is made of flexible and rigid links coupled by means of ideal joints. Once the global stiffness and inertia matrices are obtained upon assembling all modules of the subsystems, two constrained optimization techniques are first employed: the fixed pose optimization and the global optimization inside a cube. The multi-objective function is focused on the first natural frequency and its distribution within the robot's constant orientation workspace. Such an optimization combines two conflicting criteria: the need to have a stiff manipulator and the requirement to have a lightweight structure. The optimization variables pertain to only geometric parameters, while considering all materials and structural parameters as defined. Equality and inequality constraints are also included limiting the total mass of the robot, links' lengths and cross section diameters. In order to avoid workspace's volume reduction, a third optimization, based on diameter resizing, is finally described.