To increase the specific energy capacity of the docking device springs of extremely durable materials are used. To manufacture screw springs a steel wire is used with a limit durability of , which provides a specific energy capacity of the springs of . Plate-like springs are made of steel bands: , w. The total mass of the spring mechanism presented above is with an energy capacity of ; thus, the specific energy capacity of the mechanism as a whole is substantially lower than for the spring . It should be noted that shock absorber springs make up a small portion of the total mass of the docking device; the mass of all the springs of the Soyuz-Salyut docking device are 4.5% of the mass of the docking mechanism and only 1.3% of the total mass of the active docking assembly. Figure 6.5 shows a unilateral action spring mechanism with a spiral spring, which is structurally linked with the friction brake. The spring is made of a steel band with with a mass of 0.18 kg and a volume of 50 cm3. It has an energy capacity of . The spiral springs have a number of advantageous properties for the electromechanical docking device: 1) good compatibility with the scheme of the mechanism as a whole; 2) efficient form of the force characteristic, providing a large initial compression; 3) substantial internal friction. A high-speed mechanism with two-stage action was developed for the Soyuz APDA with initial preliminary compression of the spiral springs during rotation to both sides from the center position with two and one (Figure 6.6) output shafts; the first ones are used in the differential block, and the second are used in the ring with guides. The springs that were used had a large specific energy capacity ; the specific energy capacity of these mechanisms overall was also rather high, . It should be noted that the sets of cam washer, which insured the high speed of the mechanism, excluded the total failure of the docking mechanism in shaft breakdown. To increase the specific energy capacity it is expedient to optimize the spring parameters (see, for example, [37]). The characteristics of the spring mechanisms, as a rule, are stable during changes in the ambient conditions and vary slightly during storage and use.
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