Detection of absolute position of robot actuator with two incremental encoders

This paper proposes an efficient detection of absolute robot arm position using dual incremental encoders. We considers a robot joint comprising a motor, a reducer, two encoder, and motor driver. An incremental(first) encoder provides motor rotor position or input position of reducer while another incremental(second) encoder does output position of reducer. A table is made where a relationship between the first and the second encoder counts is recorded. The key point is placed where the table is constructed: when a pulse occurs in the second encoder, there exist a corresponding unique count value of the first encoder. The absolute position is detected using the table by searching the second encoder position corresponding to the first encoder count value when a pulse occurs in the second encoder. The proposed method needs a small rotation, just one second encoder's pulse angle, for the initial absolute position detection.