Brushless DC motor for dental tools - uses permanent magnet rotor position to switch logic gates controlling stator windings

摘要

The instant at which the stator windings of the brushless DC motor must be switched in sequence is determined by detecting the passage of the rotor zero field axis past appropriately positioned magnetic detectors. The resultant detector signal is fed to logic AND gates which switch the stator winding current in the required manner. Hall generators (7, 8) may be used for rotor null detection, with level detectors (9, 10, 11, 12) to give a logic 1 or 0. The detector outputs (US1-US4) are then applied to the logic AND gates (13, 14, 15, 16) to control power amplifier (17, 18, 19, 20) feeding the stator windings (2, 3, 4, 5). The necessary 90 deg. signal is synthesised by the logic to switch the windings in the desired sequence without undesirable overlap.