Figure 3.16. Rall-screw converter of the docking mechanism. 1. additional screw support; 2. four-track ball bearing; 3. casing; 4. baffle; 5. nut; 6. screw. The moment of inertia of the nut increases almost proportionally to its width, that is, the pitch s for a given number of turns; thus, as follows from the formula, as the pitch increases, decreases. The increase in pitch also increases the efficiency of transmission, especially in the conversion of forward motion to rotary motion. It is telling that if one does not take special measures to reduce the inertia of the nut, the applied mass is unacceptably high. Thus, in Table 3.2 the value of , the same for the nut of the large screw of the Soyuz docking device, is more than 1.5 tonnes (naturally, this nut does not work during shock absorption). The support capacity of the ball-screw converter is mainly defined by the contact durability of the contact grooves. The most technologically efficient are screws and nuts made of steel which also have a relatively high contact durability. The working surfaces of these screws and nuts are cemented (hardness ; acceptable contact stresses to 500 kN/cm2). To increase the support capacity and the efficiency of transmission an arched profile is used (see Figure 3.24) with the ratio of the radii of arc and the ball with an angle of contact .
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