Round pin b of link 3 fits into round recess a of link 1. One T-shaped end e of link 4 slides along T-slot guide d of link 3. The other T-shaped end c of link 4 slides along T-slot guide f of link 2. With respect to each other, links 1 and 2 accomplish one turning motion about axis x-x, and three translational motions along perpendicular axes x-x, y-y and z-z.
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