Workspace and performance analysis of a 6-DOF hexapod-type manipulator with a circular guide

The present paper considers workspace and performance analysis of a six degree-of-freedom hexapod-type parallel manipulator with a circular guide. Compared to other similar manipulators, the design of this one allows locating all the drives fixed on the base and avoiding collisions between the carriages. The first half of the paper focuses on a procedure to determine the constant orientation (translation) workspace. The study first considers all the constraints that can affect the working area: constraints in active and passive joints, leg interference, and singularities. Next, the paper discusses the numerical procedure to construct the workspace. The proposed innovative approach combines the features of conventional geometrical and discretization methods. The suggested techniques are implemented in a MATLAB package and verified by examples with various orientations of the mechanism output link. The paper also discusses the accuracy of developed methods and mentions the required computational efforts. The second half of the work analyzes manipulator performance by calculating the conditioning index over the workspaces obtained earlier. The paper evaluates the conditioning index for an ordinary Jacobian matrix and a normalized one. In the latter case, two normalization approaches are considered: using a characteristic length and using linear velocities of three points selected on the mechanism output link.