A linear encoder using a chiaroscuro and its extension to switched reluctance motor drive

In switched reluctance motor drives, the on-off switching angle of each phase switch should be accurately controlled to stabilize torque and speed. However, as the speed of a motor increases, the switching angle is prone to deviate from a preset value. Because the accuracy of the switching angle largely depends on the resolution rate of the equipped encoder, which provides a digital controller with positional information of the rotor. It also relies on the sampling performance of the digital controller. To solve these problems, a new linear encoder is proposed. It consists of a chiaroscuro plate, phototransistors and a simple logic circuit. The resolution rate of the proposed encoder is sufficiently high owing to its inherent linear characteristic. It is, moreover, not affected by the sampling performance of the microprocessor. Consequently, an accurate on-off switching signal can be produced at any desired position with high precision, regardless of the speed of motor. It also can save system cost due to its simple structure. The validity of the proposed encoder scheme is verified by experiments, and then, the result is compared to that of the conventional scheme.