Sewing machine

摘要

A sewing machine has a base plinth with an upright column supporting a horizontal overhead arm containing a motor-driven shaft with a rotor (40) and a stator (33). The rotor (40) has a rotor body (41) with a cylindrical outer wall (52). The rotor body has a number of embedded permanent rectangular magnets (46). The rotor (41) outer wall edge (53) has a series of concave detents (54), each of which engages with a matching opposite protrusion (53). The concave detents (54) are grooves or circle sectors. The depth (T) of the concave detents (54) is comparable with the rotor residual thickness (S) between the detent (54) and the sockets for the permanent magnets (46). The depth is between one half and twice that of the residual thickness.