| 摘要 |
PURPOSE:To sense correct rotor rotating speed signal with a simple constitution by taking out starting voltage from the middle point of the star-connected armature coils of a brushless motor. CONSTITUTION:Armature coils 1a-1c are star-connected for a 3-phase brushless motor. The driving circuit 5 senses rotational position of the permanent magnet rotor with a Hall element, driving current is commutated by changing over successively through each coil of the tester. The potential VN at the neutral point of start-connected armature coils is the sum of the inverse electro-motive force of the coil on the earth side and the voltage drop developed in a winding coil by the above mentioned commuted current. The potential VN, therefore, changes for each change-over interval, and the potential VN of the neutral point has amplitude with the center at 1/2 of the voltage of the power source. The amplitude is proportional to the speed, and its wave shape repeats itself 6 times for one rotor rotation, and the voltage is compared with the 1/2 of the electric source voltage to issue speed signal at a comparator 3. Next, at the control circuit 4, difference from the target value is detected to control speed. |
