Round trunnions b of link 3 turn and slide along oval guides a of link 1. Square body c of link 2 fits into the square hole of link 4 which has square trunnions d. Link 2 has prongs e with square holes sliding along trunnions d. With respect to each other, links 1 and 2 accomplish one turning motion about axis y-y, and three translational motions along perpendicular axes x-x, y-y and z-z.
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