Tor insuring compatibility were planned at the end of 1972 for verification, and joint testing of these models was done. The process of linking the APDAs, in contrast to the “rod and cone” docking mechanism, is significantly more complex. Linkage occurs only in full alignment of the rings with the guide protrusions. Thus, the energy needed to shift the rings should be small, since it is necessary to provide linkage even at small approach velocities and significant initial displacements of the spacecraft. As a result, in the general case it was necessary to make linear and angular adjustments of the ring of the active assembly in an arbitrary direction, and the size of these movements could be rather large. Thus, it was necessary to install the ring on rods which would provide good mobility (large displacements at small forces). The kinematic schematic of the model of the APDA for the Soyuz (Figure 1.27) includes five basic differentials to link the nuts of the bearing-screw converters and the drive of the docking mechanism. This connection provided movement of the ring with five degrees of freedom (along the transverse axes y and z and rotation by roll, pitch, and yaw relative to the X, y, and z axes). The sixth degree of freedom (movement along the x axis) was provided by the application of a force sufficient to turn the friction self-adjusting brake. The brake was installed between one of the differentials and the drive, and was also a protective coupling for the work of the latter. Absorption of the energy in shock absorption and the return of the ring to the equalized position was done by five spring mechanisms, and damping was provided by electromagnetic brakes. To simplify the spring mechanisms and the brakes, and to make the characteristics of the shock absorbers independent of shifting along various coordinates, five additional differentials were introduced. The experience of work with the model and subsequent analysis confirmed the correctness of the basic idea of the construction of the docking mechanism with differential connections. At the same time, drawbacks were detected in the scheme: the large number of elements in the kinematic circuits, significant friction, and inertia. In order to eliminate these drawbacks, a simpler and more efficient docking mechanism was developed (Figure 1.28). Here the nuts of the bearing-screw converters in each pair of rods were kinematically linked together, and mismatches in the lengths of the rods in the pair, to provide for transverse displacement of the ring (including roll displacements) occur due to rotation of the screws themselves.
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