The lengths of the links comply with the conditions: A͞C=D͞B and A͞D=C͞B. Cranks 1 and 3 are designed as round eccentrics rotating about fixed axes A and D. Connecting rod 2 has collars encircling these eccentrics. When eccentric 1 rotates clockwise, eccentric 3 rotates counterclockwise. At the right-hand extreme (dead-centre) position of the mechanism, gear segment b of eccentric 1 meshes with gear segment a' of eccentric 3. At the left-hand extreme (dead-centre) position, gear segments a and b' mesh. As a result uncertainty of motion of the mechanism is eliminated. The mechanism is equivalent to two meshing elliptical gears c and d with the foci of the ellipses at points A, C, B and D.
$1736$GL,4L$