Mechanical structure for high speed locomotion of MEMS microrobot using SMA rotary actuator

Abstract

The hexapod legs of insects achieve stable walking motions on various surfaces. This paper proposes a walking hexapod microrobot that mimics an insect's walking behavior. Miniaturization of the robot is an important issue. The miniaturized robotic component is fabricated by the micro electro mechanical systems (MEMS) process, which is based on the IC production process using silicon wafer as the starting material. The miniature rotary actuator is constructed from miniature silicon components and an artificial muscle wire based on shape memory alloy (SMA). The material property of SMA enables the miniaturization of the actuator. Four artificial muscle wires, which shrink by a heating process, are attached to the rotor in a four-through pattern. The joining material is a conductive paste. A rotary motion is generated by successively passing an electric current to the artificial muscle wire. Continuous heating shrinks the artificial muscle wire, decreasing its displacement during the rotational motion. Therefore, the actuator requires a cooling process, which reduces its operating speed. To achieve high-speed operational walking of the MEMS microrobot locomotion by the artificial muscle wire actuator, a two-hole-type rotor with low heat capacity was developed, and its thermal distribution and heat transition were observed. Also, the lead wires of the artificial muscle wire are located inside the microrobot's body. After externally connecting with a pulse-type artificial neural network IC controller developed by us, the microrobot traveled at 21.2 mm/min.