Development of ultra-small sized servo actuator with brushless DC motor, planetary gear drive and optical rotary encoder

Abstract

An ultra-small sized actuator with high output torque at low rotation speed has been developed for applications to servo driving of micro-machines such as micro-robots. It consists of a micro-brushless DC motor, a planetary gear drive, and an optical rotary encoder. In this report, each element technology, output characteristics of the actuators and an application of the actuators to a micro-SCARA type robot are described. The brushless DC motor has a rotor with two poles of samarium cobalt magnets and three thin stator coils of fine copper wires. The planetary reduction gear drive has only six micro-gears with mechanical paradox. The optical rotary encoder has a metal circular scale with 75 slits and two optical glass fibers, and monitors rotation of the motor. Two prototypes of different sized actuators were developed: one is 3 mm in diameter and 10 mm in length, and the other is 5 mm in diameter and 18 mm in length, and were applied to a micro-SCARA type robot.