1. Clavel R. Device for the movement and positioning of an element in space. US Patent #4,976,582.
2. Hvittfeldt H, Larsson J, Mikaelsson P, Persson F. Manipulator and method for manufacturing the manipulator. US Patent #6,419,211.
3. INA, Parallel Robot Joints Catalog. INA-Schaeffler KG. Industriestrasse 1–3. 91074 Herzogenaurach: Germany; 2003.
4. Bieg LF, Benavides GL. Double slotted socket spherical joint. US Patent #6,234,703.
5. Kinematic analysis and optimization of a new three-degree-of-freedom spatial parallel manipulator;Carretero;ASME J Mech Des,2000