A Practical Method for Solving the Direct Kinematics of Stewart Platform Using Extra Rotary Sensors

A novel and practical method is proposed for real-time solution of forward kinematics of Stewart platform (SP). It is based on nine measurements on non-adjacent legs which three of them are the legs’ lengths and the remaining six ones are rotations of lower universal joints. The available alternative methods are variants of: ۱- the conventional method which uses the length measurements of all six legs and ۲- the methods use extra length measurements other than those of six legs. The proposed method is categorized into the aforementioned ۲nd methods. After the application of the proposed method on a laboratory sample SP, and comparing it with the available methods it is observed that the proposed method is simpler in implementation, more practical, less expensive and easier in maintenance. The algorithm of forward kinematics is fully derived based on geometric relationships between the platform states and the measurement data. A procedure for the inverse kinematics is also derived for the purpose of simulation of the main algorithm. The algorithm is implemented on the sample SP both in practice and computer simulation. For validation of the proposed method, a parallel formulation is derived based on Newton-Raphson approach for the conventional method and parallel simulations are performed for the conventional and the proposed methods and analogous results are obtained.

Keywords:

Forward Kinematics , Direct Kinematics , Stewart-Platform