Link 1 which is one sliding member has prongs a with square holes which fit over square guides b of link 3. Sliding member 4 travels in box-shaped guide e of link 3. Sliding member 4 consists of spherical half-collars c which fit over ball-shaped head d of link 2. With respect to each other, links 1 and 2 accomplish three turning motions about perpendicular axes x-x, y-y and z-z, and two translational motions along perpendicular axes x-x and y-y.
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