Figure 6.9 [left]. Variant of the APDA electromagnetic brake. 1. output shaft; 2. full rotor; 3. external magnet; 4. internal magnet; 5. additional support. Figure 6.10 [right]. Electromagnetic brake with by-pass coupling. 1. gear; 2. bypass coupling; 3. electromagnetic brake. Figure 6.10 shows an electromechanical brake with a miniature by-pass coupling installed on its shaft. This construction makes it possible to obtain a coefficient of attenuation which depends on the direction of displacement of the rod of the shock absorber. To evaluate the reliability of the electromagnetic brake, breakdowns and jamming of the rotor is examined (full and partial). Most critical is a full jamming; thus, it is expedient to use shearable elements, such as pins, on the output shaft. In addition to the electromagnetic brake with permanent magnets for shock absorbers with controllable characteristics, the use of brakes is possible. Evaluations show that the controllable brake with independent stimulation is larger in mass and size than an electromagnetic brake with permanent magnets with the same brake momentum. The current of stimulation of this brake is equal to several amperes, which is due to the large air gap. To decrease the current of stimulation and increase the brake momentum, it is expedient to use the currents of the rotor for magnetization, that is, to use a structure with self-stimulation of the gap. The basic problem is the removal of the currents of the mobile rotor into the stator. The use of collectors reduces the reliability of the system and substantially increases the moment of friction in the rotor.
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