Patent ID: 6104155
Filing Date: 2000-08-15
Classification: H02P

Abstract:
An electric motor comprising:an armature;a field coil;means to interconnect the armature and the field coil;a switching means (i) operable in a first mode for connecting the armature and the field coils to a first supply voltage to drive the armature, (ii) operable in a second mode for short circuiting the armature, connecting a second voltage less than the first supply voltage to the field coils and thereby braking the motor, and (iii) operable in a third mode for disconnecting the first supply voltage from the armature and the field coils;means operating continuously in a consistent monitoring mode during at least the second mode independently of the operational condition of the motor during the first mode and the second mode for determining when a voltage in circuit with the field coil reaches a prescribed threshold voltage level;brake control means responsive to the voltage in circuit with the field coil reaching the prescribed threshold voltage level for controlling operating of the switching means to change the switching means from the second to the third mode; anda variable voltage control means for controlling the magnitude of the voltage across the field coils so that (i) in the first mode of the switching means, the first supply voltage is applied to the field coils by the voltage control means and (ii) in the second mode of the switching means, the second smaller voltage is applied to the field coils by the voltage control means.