Concrete vibrator

摘要

A concrete vibrator is provided in which a semiconductor (solid-state) motor without a sensor is used as the drive. The semiconductor motor without a sensor has an arrangement such that the rotary position of the permanent magnet rotor is determined on the basis of a voltage which is generated by three-phase stator windings, that is to say a voltage which is induced in accordance with the distribution of the magnetic flux in the gap and which varies its frequency only with the rotational speed without there being a need for a Hall element which is easily damaged by vibrations and heat, that is to say has only a very low robustness (toughness, resistance). Moreover, the semiconductor motor without a sensor is arranged in such a way that the power is supplied to the stator winding under the control of a semiconductor invertor which, for its part, is controlled by pulse-width modulation or pulse-amplitude modulation.