Gear 1 rotates about fixed axis E and meshes with gears 3 and 4, of equal pitch diameter, which rotate about fixed axes D and A. Gears 3 and 4 are connected by turning pairs C and B to link 2 which carries the kneading member b. The dimensions of the links comply with the conditions: A͞B=D͞C and A͞D=B͞C. Thus figure ABCD is a parallelogram and therefore, when gear 1 rotates, any point K of member b describes circle q of a radius
r=A͞B.
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