Pin b of link 3 fits into hole a of link 1. Link 3 has, at its other end, box-shaped rectan- gular guide d along which sliding member 4 travels. Sliding member 4 has spherical half- collars e fitting over barrel-shaped head c of link 2. With respect to each other, links 1 and 2 accomplish four turning motions about the three perpendicular axes intersecting at point 0 and about axis x' -x' , and one translational motion along an axis square to the plane of the drawing.
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