Edinburgh Napier University

  The capacities of parallel mechanisms are limited by their height for the narrow space applications, such as the shipboard stability platforms, household simulators, aerospace mechanisms, etc. This paper proposes a novel foldable six-DOF parallel manipulator which has three main limbs with each actuated by two actuators. With the ability to fold in the vertical direction, this mechanism can be deployed from a height of about 0.278 m to 2.218 m, and the required driving stroke is only 0.67 m by the analysis results of the workspaces. However, this stroke enlargement leads to large driving forces. In order to improve the capacity for the heavy loading of this foldable mechanism, each leg is assisted by a balance spring. Static and dynamics models are built for the calculation of the driving forces and constraint forces. Two methods to calculate the optimal balance force for objective driving force are also proposed and based on the designed trace in the workspace, the springs’ linear stiffness is optimized. The simulation results demonstrate that the actuators’ driving forces are much reduced, and the homogeneity between the fully folded and deployed configuration is much improved by adding balance springs.