The linkage is done when the rings are aligned with the guides; thus, the sensors are located on the faces of these rings. No less than three sensors are necessary for each ring of an androgynous assembly. For linkage one must compress the plungers of all the sensors; as a rule rigid requirements are imposed on the minimum force of actuation, exclusion of jamming of the plunger, etc. The ring with guides usually has three drives to release the latches. The small power and, as a result, the speed of activation of drives makes it possible to avoid the use of special measures to synchronize their operation. 2.8. Comparative Analysis of the Principle Schemes of Docking Mechanisms In this section the results of analysis of various schemes of docking mechanisms are presented. Three types of mechanisms are analyzed: sequential, parallel, and combined. Simplified analysis of the effect of potential failures of the drive and shock absorbers on docking shows (Table 2.7) that jamming failures have less effect on today's shock absorption-drive system. The results refer to both types of docking device: “rod and cone” and peripheral. More definite and detailed results may be obtained in a similar analysis of specific schemes of docking devices. Naturally in practice in the selection of a scheme one considers a whole complex of properties of the docking device, as well as the conditions of its creation. This analysis makes it possible to make a more valid choice of a scheme and aid in its improvement. An important parameter is the maximum longitudinal size of the docking mechanism. For the Soyuz-Salyut complex (see section 1.5.1) it was necessary to create a docking mechanism with a significantly shorter longitudinal size than in the mechanism created earlier for the Soyuz craft. This was done mainly by switching from a parallel scheme to a combined one. Tn peripheral docking devices the advantages and drawbacks of all three types of docking mechanism are becoming more and more clear. The shock absorbers of peripheral docking mechanisms have a relatively longer course; thus the ring with guides should also be extended further. As a result the parallel scheme is virtually inapplicable for peripheral docking devices. The use of differential connections between the rods of the docking mechanism permit one to make full use
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