Round trunnions b of link 3 slide along oval guides a of link 1. Square body d of link 3 fits into the square hole of link 4 which slides along link 3. Link 4 also has rectangular projections which slide in guides e 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 three perpendicular axes x-x, y-y and z-z.
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