Link 1 has hole e fitting on cylindrical portion k of link 4, which has two ball-shaped heads a and b. Head a fits into sliding member 3 and head b into link 2. Sliding member 3 moves between flat surfaces d of link 2. With respect to each other, links 1 and 2 accomplish two turning motions about perpendicular axes x-x and y-y, and one translational motion along axis x-x.
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