Brush-less servomotor

A brush-less servomotor has been developed by using interdisciplinary mechatronics engineering. A mechanical switching device (commutator) is replaced by electronic circuits and controllers resulting in maintenance free and high performance servo drive.
The brush-less servomotor is an ac motor, in all respects and is in fact called the ac servomotor. Combined with a dedicated control device, the performance of the brush-less servomotor is found to be equal to the performance of the high performance dc servo motor.
The rotational speed of dc servomotor is generally varied by changing the voltage applied to the armature. As the armature voltage is nearly proportional to the rotational speed, the speed can be slowed down as much as is required by lowering the applied voltage. On the other hand the rotational speed of the ac motor is generally varied by changing the frequency. However the frequency has its limits of variation. A wide range of speed variation, which is a feature of servomotors, cannot be obtained by using only a simple inverter.
In dc motor when the current flows in the electrical conductor, after passing through the brushes and the commutator in the magnetic field generated by permanent magnets N and S, torque is generated. For getting a stable torque proportional to current, the line of magnetic force should intersect the c of current at right angles in a dc motor. This is enabled by the use of rectifiers (a commutator and brushes).
In ac motors slip ring is used instead of a commutator and a power source of alternating current makes the rotor rotate continuously at the rotational speed corresponding to the applied frequency. But the brushes of the ac motors can be eliminated by changing the revolving armature structure in to revolving field type.