The force in the sixth degree of freedom (longitudinal shifting of the ring) is substantially larger. This correlation prevents the ring from approaching the docking frame before linkage, and requires the minimum course in the absorption of the majority of the energy after linkage. In a parallel scheme, to provide for mobility of the ring before linkage it is necessary for the characteristics of the shock absorbers to have an initial soft stage; as a result the ring easily approaches the frame, which reduces the range of shifting in the remaining coordinates (see section 5.6.7). Due to the differential connections it is easy to provide the necessary equalization of the ring with guides with a force developed by the docking mechanism drive during extension; thus, it is possible to execute this operation with partial jamming in the rods or shock absorbers. This property permits further reduction of the force of the shock absorbers during displacements in five degrees of freedom. In the parallel scheme of the docking mechanism the equalization of the ring is the same in that it is extended by the force of the springs of the shock absorbers. The differential connections make it possible to fix the ring with rings from moving in five degrees of freedom. Fixation provides for extension and retraction of the ring even when there is partial jamming of the rods or shock absorbers. The fixing devices prevent the ring from warping even when affected by external forces, for example, from the control system of the spacecraft. The drive of the docking mechanism constructed from the parallel scheme should, in coupling, overcome the force of the shock absorption springs and the hydraulic dampers. This applies to “rod and cone” type and peripheral docking devices. This reduces the force of coupling of the docking frames. Moreover, in peripheral docking mechanisms there may be a difference in the force of the shock absorbers due to tolerances and drops in temperature; this causes warping of the ring, and in the final portion, loading of the guide rods and sockets of the docking frames. In the combined scheme there is no warping of the ring. In a combined docking mechanism with differential connections it is easy to install sensors to signal deviations of the ring in five degrees of freedom. These sensors are used to monitor the equalized position of the ring when it is extended before docking, during equalization, and coupling.
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