It is possible to use a contactless electromagnetic brake scheme with an electrically asymmetrical rotor, which makes it possible to transform the mechanical energy of the rotor into the electric stator. The pulsing current of the rotor induces FMF in the generator winding of the stator, which is connected with the stimulation winding. To increase the coefficient of attenuation after linkage one can also use a friction controlled brake with the compression of the disks using an electromagnet, or the combination of an electromagnetic brake with permanent magnets and a controllable friction coupling. 6.5. Hydraulic and Pneumatic Shock Absorbers Docking devices created in the US use hydraulic shock absorbers. In addition to clear advantages (high efficiency, low inertia) hydraulic dampers have a number of drawbacks which are mainly associated with the presence of seals, possible leaks, and a change in the viscosity and volume of liquid, primarily during heating and cooling. The friction in the seals may be significant, which has a negative effect on several characteristics of the docking mechanism as a whole. Tn the shock absorbers of the docking mechanisms of the Apollo spacecraft, in addition to the central screw spring, a pneumatic spring is used (Figure 6.11). Compressed argon creates a force of 1.9 kN at normal temperature, and it compensates for the temperature expansion of the liquid. Hermeticity is provided by resin rings and a metallic bellows, eliminates the leakage of compressed gas or liquid (a significant leak may lead to a breakdown of the shock absorber). The shock absorber is capable of work in temperatures from ; however, its characteristic changes substantially despite the use of a special liquid by-pass regulator which is sensitive to viscosity. The coefficient of attenuation changes by almost a factor of two, and the force of the pneumatic springs by a factor of 1.9. The mass of the shock absorber is 2.5 kg, thus, (the shock absorber creates a force of about 6 kN at a deformation velocity of, with a maximum course of 0.08 m).
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