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This paper strives to compare between two 3-Degree of Freedom (DoF) Spatial Parallel Manipulators (SPMs) belonging to the 3-[PP]S-Y family viz., 3-RRS and 3-RPS. The planes of the manipulators belong to this family are arranged in a Y-pattern such that they intersect at 120° in a common line. Both of these manipulators have a common motion of 1T2R (T: Translation, R: Rotation) type, and their comparison in this work is carried out by considering the effects of link tolerance and parasitic motions, for the same task space and End-Effector (EE) positions. Their respective position kinematic analysis is discussed initially. The comparison is then carried out by considering two different cases based on the sizes of the moving platform relative to the base platform. The errors are quantified and all the comparative results are represented with the aid of plots. The conclusions are summarized at the end that allow to know the better of the two manipulators for the given effects.

This paper presents the mechanical error estimation under the effects of link tolerances in a 3-degree-of-freedom (DoF) 3-RRS Spatial Parallel Manipulator (SPM). Position level kinematic analysis and workspace analysis in the form of reachable and orientation workspace are carried out initially. Then, the effect of link tolerances on individual link is studied at the position of mid-point and orientation of the movable platform. The corresponding mechanical errors are estimated. The effect of link tolerance variation is studied to know the pattern of mechanical error. The 3-D CAD model in SolidWorks is used to validate the results. The conclusions are drawn that lead to error minimization at the tolerance design stage.