In a linkage coupling having a single-axis rotary joint, two joint parts rotatable relative to one another and capable of being fixed in different rotary-angle positions relative to one another are used. For guiding an eccentric pin parallel to the joint axis, one joint part has a radial guide slot and the other joint part has a guide slot extending in the circumferential direction with a variable radius. It thereby becomes possible to change the effective length of one linkage part connected to the eccentric pin, without changing the instantaneous conditions on the other linkage part, on which the joint part having the radial guide slot is fixed immovably.
