Three-phase brushless servo motor

摘要

A three-phase alternating current voltage signal composed of three alternating current voltage signals, of which phases are shifted from each other by an electric angle of 120 degrees, is produced in three Hall devices according to a Hall effect caused by an interaction between the Hall devices and a magnetic unit when the magnetic unit is rotated at a rotational speed in a three-phase brushless servo motor. In this case, because inclinations of straightly-rising line portions and straightly-falling line portions in each alternating current voltage signal indicate the rotational speed of the magnetic unit, the straightly-rising line portions and the straightly-falling line portions are extracted from the three-phase alternating current voltage signal and are connected to each other to produce a first wave-form processed signal indirectly indicating the rotational speed, and the first wave-form processed signal is differentiated to produce a second wave-form processed signal directly indicating the rotational speed. A servo control is performed for the three-phase brushless servo motor according to the second wave-form processed signal to adjust the rotational speed to a target rotational speed. Accordingly, the rotational speed in the three-phase brushless servo motor can be maintained to the target rotational speed without any rotational speed detecting encoder.