This paper presents a novel method based on screw theory for the analysis of positioning accuracy in parallel manipulators with joint clearances. A general method is introduced, and a new analytical procedure is formulated which allows to determine analytically a sub-optimal estimation of the worst case condition for positioning accuracy. Moreover this procedure can determine exactly the worst-case angular accuracy in translating fully-parallel manipulators under the influence of joint

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... s. The relevance of the method is demonstrated by two application examples, that clearly demonstrate how kinematic properties, such as kinematic isotropy, are strictly related to position accuracy in mechanisms with joint clearances.