Spatial mechanisms have been an intensive area of research for over a decade, for their advantages such as good stiffness, large load capacity, and high accuracy, in comparison with the traditional serial mechanisms. The arm manipulators require an actuator for each axis, and a large number of degrees of freedom DOF, which make them expensive. In this case, the spatial mechanism can replace the serial manipulator. If we could design spatial mechanisms quickly and easily, there may be more applications using these mechanisms. The aerospace industry, sports training equipment and rehabilitation in the medical field already use some examples of these systems. In this paper, we analyze the proposed model of spatial mechanism based on kinematic and geometric criteria, the simulation results shows that varied values of the size of the fixed base and the length of the prismatic joint of the mechanism, the workspace takes different forms. This variation can be used to design the 3 UPU robot for specific applications.