Analysis and application of the singularity locus of the Stewart platform

The direct use of the determinant of Jacobian matrix being equal to zero for the singularity analysis is generally difficult which is due to complexity of the Jacobian matrix of 6-DOF parallel manipulators, especially for Stewart platform. Recently, several scholars make their great contribution to the effective solution of this problem, but neither of them find the right answer. This paper gives a brief analysis of the kinematics of the Stewart platform and derives the Jacobian matrices of the system through the velocity equation. On the basis of the traditional classification of singularities, the second type of singularity is investigated. An assumption of any three of the six variables of the Stewart platform as constant is made, then the analytical expression of singularity locus equation of the second type singularity which contains another three pose variables is obtained. The singularity locus is represented in the three-dimensional space through the derived equation. The correctness and validity of the proposed method are verified through examples. Finally, the singularity analysis of an electric Stewart platform in its desired workspace and reachable workspace is implemented. Thus, one can easily identify whether singularity exists in a given workspace of a Stewart platform and determine whether the existed singularity can be avoided through the proposed method. The proposed method also provides theoretical principle for the design and application of the Stewart platform and has great significance for the trajectory planning and control.